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These are my current errors, I think I did something wrong with the maths but everything I tried didn't work.
Ps: Sorry if my question's formatting is bad, first time using stackflow.
:) credit.c exists
:) credit.c compiles
:) identifies 378282246310005 as AMEX
:) identifies 371449635398431 as AMEX
:) identifies 5555555555554444 as MASTERCARD
:) identifies 5105105105105100 as MASTERCARD
:) identifies 4111111111111111 as VISA
:) identifies 4012888888881881 as VISA
:) identifies 4222222222222 as VISA
:) identifies 1234567890 as INVALID
:) identifies 369421438430814 as INVALID
:) identifies 4062901840 as INVALID
:) identifies 5673598276138003 as INVALID
:( identifies 4111111111111113 as INVALID
expected "INVALID\n", not "VISA\n"
:( identifies 4222222222223 as INVALID
expected "INVALID\n", not "VISA\n"
#include <cs50.h>
#include <math.h>
// Prompt user for credit card number
int main(void)
{
long credit_card, credit_number;
do
{
credit_card = get_long("Enter credit card number: ");
}
while (credit_card < 0);
credit_number = credit_card;
// Calculate total number of digits
int count = (credit_number == 0) ? 1 : (log10(credit_number) + 1);
int summation = 0;
while (credit_number == 0)
{
int x = credit_number % 10; summation += x;
int y = 2 * ((credit_number / 10) % 10);
int r = (y % 10) + floor((y / 10) % 10); summation += r; credit_number /= 100;
}
string card;
// Identify which card type you get after inputing your credit card number
int test = cc / pow(10, count - 2);
if ((count == 13 || count == 16) && test / 10 == 4)
{
card = "VISA";
}
else if (count == 16 && test >= 51 && test <= 55)
{
card = "MASTERCARD";
}
else if (count == 15 && (test == 34 || test == 37))
{
card = "AMEX";
}
else
{
card = "INVALID";
}
// Final verification
if (sum % 10 == 0)
{
printf("%s\n", card);
}
else
{
printf("INVALID\n");
}
}```
Your algorithm is maybe not fully correct. I would therefore propose a different approach. You can look at each single digit in a loop. And, you can also do the whole checksum calculation in one step.
I will show you how to do and explain the algorithm behind it.
BTW. Chosing the right algorithm is always the key for success.
So, first we need to think on how we can extract digits from a number. This can be done in a loop by repeating the follwoing steps:
Perform a modulo 10 division to get a digit
Do a integer division by 10
Repeat
Let us look at the example 1234.
Step 1 will get the 4 -- (1234 % 10 = 4)
Step 2 will convert original number into 123 -- (1234 / 10 = 123)
Step 1 will get the 3 -- (123 % 10 = 3)
Step 2 will convert the previous number into 12 -- (123 / 10 = 12)
Step 1 will get the 2 -- (12 % 10 = 2)
Step 2 will convert the previous number into 1 -- (12 / 10 = 1)
Step 1 will get the 1 -- (1 % 10 = 1)
Step 2 will convert the previous number into 0 -- (1 / 10 = 0)
Then the loop stops. Additionally we can observe that the loop stops, when the resulting divided becomes 0. And, we see addtionally that the number of loop executions is equal to the number of digits in the number. But this is somehow obvious.
OK, then let us look, what we learned so far
while (creditCardNumber > 0) {
unsigned int digit = creditCardNumber % 10;
creditCardNumber /= 10;
++countOfDigits;
}
This will get all digits and count them.
Good. Lets go to next step.
For later validation and comparison purpose we need to get the most significant digit (the first digit) and the second most significant digit (the second digit) of the number.
For this, we define 2 variables which will hold the number. We simply assign the current evaluated digit (and override it in each loop execution) to the "mostSignificantDigit". At the end of the loop, we will have it in our desired variable.
For the "secondMostSignificantDigit" we will simple copy the "old" or "previous" value of the "mostSignificantDigit", before assigning a new value to "mostSignificantDigit". With that, we will always have both values available.
The loop looks now like this:
while (creditCardNumber > 0) {
const unsigned int digit = creditCardNumber % 10;
secondMostSignificantDigit = mostSignificantDigit;
mostSignificantDigit = digit;
creditCardNumber /= 10;
++countOfDigits;
}
OK, now we come to the maybe more complex part. The cheksum. The calculation method is.
Start with the least significant (the last) digit
Do not multiply the digit, which is equivalent with multiplying it with 1, and add it to the checksum
Goto the next digit. Multiply it by 2. If the result is greater than 10, then get again the single digits and add both digits to the checksum
Repeat
So, the secret is, to analyze the somehow cryptic specification, given here. If we start with the last digit, we do not multiply it, the next digit will be multiplied, the next not and so on and so on.
To "not multiply" is the same as multiplying by 1. This means: In the loop we need to multiply alternating with 1 or with 2.
How to get alternating numbers in a loop? The algorithm for that is fairly simple. If you need alternating numbers, lets say, x,y,x,y,x,y,x..., Then, build the sum of x and y and perform the subtratcion "value = sum - value". Example:
We need alternating values 1 and 2. The sum is 3. To get the next value, we subtract the current value from the sum.
initial value = 1
sum = 3
current value = initial value = 1
next value = 3 - 1 = 2. Current value = 2
next value = 3 - 2 = 1. Current value = 1
next value = 3 - 1 = 2. Current value = 2
next value = 3 - 2 = 1. Current value = 1
next value = 3 - 1 = 2. Current value = 2
next value = 3 - 2 = 1. Current value = 1
. . .
Good, now we understand, how to make alternating values.
Next, If we multiply a digit with 2, then the maximum result maybe a 2 digit value. We get the single digits with a modulo and an integer division by 10.
And, now important, it does not matter, if we multiply or not, because, if we do not multiply, then the upper digit will always be 0. And this will not contribute to the sum.
With all that, we can always do a multiplication and always split the result into 2 digits (many of them having the upper digit 0).
The result will be:
checkSum += (digit * multiplier) % 10 + (digit * multiplier) / 10;
multiplier = 3 - multiplier;
An astonishingly simple formula.
Next, if we know C or C++ we also know that a multiplication with 2 can be done very efficiently with a bit shift left. And, additionally, a "no-multiplication" can be done with a bit shift 0. That is extremely efficient and faster than multiplication.
x * 1 is identical with x << 0
x * 2 is identical with x << 1
For the final result we will use this mechanism, alternate the multiplier between 0 and 1 and do shifts.
This will give us a very effective checksum calculation.
At the end of the program, we will use all gathered values and compare them to the specification.
Thsi will lead to:
int main() {
// Get the credit card number. Unfortunately I do not know CS50. I use the C++ standard iostream lib.
// Please replace the following 4 lines with your CS50 equivalent
unsigned long long creditCardNumber;
std::cout << "Enter credit card number: ";
std::cin >> creditCardNumber;
std::cout << "\n\n";
// We need to count the number of digits for validation
unsigned int countOfDigits = 0;
// Here we will calculate the checksum
unsigned int checkSum = 0;
// We need to multiply digits with 1 or with 2
unsigned int multiplier = 0;
// For validation purposes we need the most significant 2 digits
unsigned int mostSignificantDigit = 0;
unsigned int secondMostSignificantDigit = 0;
// Now we get all digits from the credit card number in a loop
while (creditCardNumber > 0) {
// Get the least significant digits (for 1234 it will be 4)
const unsigned int digit = creditCardNumber % 10;
// Now we have one digit more. In the end we will have the number of all digits
++countOfDigits;
// Simply remember the most significant digits
secondMostSignificantDigit = mostSignificantDigit;
mostSignificantDigit = digit;
// Calculate the checksum
checkSum += (digit << multiplier) % 10 + (digit << multiplier) / 10;
// Multiplier for next loop
multiplier = 1 - multiplier;
creditCardNumber /= 10;
}
// Get the least significant digit of the checksum
checkSum %= 10;
// Validate all calculated values and show the result
if ((0 == checkSum) && // Checksum must be correct AND
(15 == countOfDigits) && // Count of digits must be correct AND
((3 == mostSignificantDigit) && // Most significant digits must be correct
((4 == secondMostSignificantDigit) || (7 == secondMostSignificantDigit)))) {
std::cout << "AMEX\n";
}
else if ((0 == checkSum) && // Checksum must be correct AND
(16 == countOfDigits) && // Count of digits must be correct AND
((5 == mostSignificantDigit) && // Most significant digits must be correct
((secondMostSignificantDigit > 0) && (secondMostSignificantDigit < 6)))) {
std::cout << "MASTERCARD\n";
}
else if ((0 == checkSum) && // Checksum must be correct AND
((16 == countOfDigits) || (13 == countOfDigits)) && // Count of digits must be correct AND
((4 == mostSignificantDigit))) { // Most significant digit must be correct
std::cout << "VISA\n";
}
else {
std::cout << "INVALID\n";
}
return 0;
}
What we learn with this example, is integer division and modulo division and the smart usage of the identity element for binary operations.
In case of questions, please ask
Just to be complete, I will show you a C++ solution, based on a std::string and using modern C++ elements and algorithms.
For example, the whole checksum calculation will be done with one statement. The whole program does not contain any loop.
#include <iostream>
#include <string>
#include <regex>
#include <numeric>
int main() {
// ---------------------------------------------------------------------------------------------------
// Get user input
// Inform user, what to do. Enter a credit card number. We are a little tolerant with the input format
std::cout << "\nPlease enter a credit card number:\t";
// Get the number, in any format from the user
std::string creditCardNumber{};
std::getline(std::cin, creditCardNumber);
// Remove the noise, meaning, all non digits from the credit card number
creditCardNumber = std::regex_replace(creditCardNumber, std::regex(R"(\D)"), "");
// ---------------------------------------------------------------------------------------------------
// Calculate checksum
unsigned int checksum = std::accumulate(creditCardNumber.rbegin(), creditCardNumber.rend(), 0U,
[multiplier = 1U](const unsigned int sum, const char digit) mutable -> unsigned int {
multiplier = 1 - multiplier; unsigned int value = digit - '0';
return sum + ((value << multiplier) % 10) + ((value << multiplier) / 10); });
// We are only interested in the lowest digit
checksum %= 10;
// ---------------------------------------------------------------------------------------------------
// Validation and output
if ((0 == checksum) && // Checksum must be correct AND
(15 == creditCardNumber.length()) && // Count of digits must be correct AND
(('3' == creditCardNumber[0]) && // Most significant digits must be correct
(('4' == creditCardNumber[1]) || ('7' == creditCardNumber[1])))) {
std::cout << "AMEX\n";
}
else if ((0 == checksum) && // Checksum must be correct AND
(16 == creditCardNumber.length()) && // Count of digits must be correct AND
(('5' == creditCardNumber[0]) && // Most significant digits must be correct
((creditCardNumber[1] > '0') && (creditCardNumber[1] < '6')))) {
std::cout << "MASTERCARD\n";
}
else if ((0 == checksum) && // Checksum must be correct AND
((16 == creditCardNumber.length()) || (13 == creditCardNumber.length())) && // Count of digits must be correct AND
(('4' == creditCardNumber[0]))) { // Most significant digit must be correct
std::cout << "VISA\n";
}
else {
std::cout << "INVALID\n";
}
return 0;
I recently learnt that using getchar_unlocked() is a faster way of reading input.
I searched on the internet and found the code snippet below:
But I am unable to understand it.
void fast_scanf(int &number)
{
register int ch = getchar_unlocked();
number= 0;
while (ch > 47 && ch < 58) {
number = number * 10 + ch - 48;
ch = getchar_unlocked();
}
}
int main(void)
{
int test_cases;fast_scanf(test_cases);
while (test_cases--)
{
int n;
fast_scanf(n);
int array[n];
for (int i = 0; i < n; i++)
fast_scanf(array[i]);
}
return 0;
}
So, this code takes input for an integer array of size n for a given number of test_cases . I didn't understand anything in the function fast_scanf, like why this line:
while (ch > 47 && ch < 58)
{ number = number * 10 + ch - 48;
why the register is used while declaring ch?
why the getchar_unlocked() is used twice in the function? and so on..
It would be great help if someone elaborates this for me. Thanks in advance!
Okay, since what you are asking needs to be explained clearly, I am writing it here... so I don't jumble it all up inside the comments...
The function: (Edited it a bit to make it look like more C++-standard)
void fast_scanf(int &number)
{
auto ch = getchar_unlocked();
number= 0;
while (ch >= '0' && ch <= '9')
{
number = number * 10 + ch - '0';
ch = getchar_unlocked();
}
}
Here, take up consideration by looking at the ASCII Table first, since you won't understand how the results are coming up if you don't...
1) Here, you have a character ch takes up the input character from the user using getchar_unlocked() (The auto keyword does that automatically for you and is only usable in C++, not C)...
2) You assign the variable number to zero so that the variable can be re-used, note that the variable is a reference so it changes inside your program as well...
3) while (ch >= '0' && ch <= '9')... As pointed out, checks whether the characters is within the numerical ASCII limit, similar to saying that the character has to be greater than or equal to 48 but less than or equal to 57...
4) Here, things are a little bit tricky, Variable number is multiplied with the product of itself and 10 and the real integer value of the character you stored)...
5) In the next line, ch is reassigned so that you don't have to stay in the loop forever, since ch will remain that number forever if the user doesn't type anything... remember a loop goes back to where it was declared after reaching the end, checks if the condition is true, continues if it is true else breaks)...
For example: 456764
Here, ch will first take 4 then the others follow so we go with 4 first...
1) Number will be assigned to zero. While loop checks if the given character is a number or not, if it is continues the loop else breaks it...
2) Multiplication of 0 with 10 will be zero... and adding it with difference 52 (that is '4') with 48 (that is '0') gives you 4 (the real numerical value, not the char '4')...
So the variable number now is 4...
And the same continues with the others as well... See...
number = number * 10 + '5' - '0'
number = 4 * 10 + 53 - 48
number = 40 + 5
number = 45... etc, etc. for other numbers...
I have a few loops that I need in my program. I can write out the pseudo code, but I'm not entirely sure how to write them logically.
I need -
if (num is a multiple of 10) { do this }
if (num is within 11-20, 31-40, 51-60, 71-80, 91-100) { do this }
else { do this } //this part is for 1-10, 21-30, 41-50, 61-70, 81-90
This is for a snakes and ladders board game, if it makes any more sense for my question.
I imagine the first if statement I'll need to use modulus. Would if (num == 100%10) be correct?
The second one I have no idea. I can write it out like if (num > 10 && num is < 21 || etc.), but there has to be something smarter than that.
For the first one, to check if a number is a multiple of use:
if (num % 10 == 0) // It's divisible by 10
For the second one:
if(((num - 1) / 10) % 2 == 1 && num <= 100)
But that's rather dense, and you might be better off just listing the options explicitly.
Now that you've given a better idea of what you are doing, I'd write the second one as:
int getRow(int num) {
return (num - 1) / 10;
}
if (getRow(num) % 2 == 0) {
}
It's the same logic, but by using the function we get a clearer idea of what it means.
if (num is a multiple of 10) { do this }
if (num % 10 == 0) {
// Do something
}
if (num is within 11-20, 31-40, 51-60, 71-80, 91-100) { do this }
The trick here is to look for some sort of commonality among the ranges. Of course, you can always use the "brute force" method:
if ((num > 10 && num <= 20) ||
(num > 30 && num <= 40) ||
(num > 50 && num <= 60) ||
(num > 70 && num <= 80) ||
(num > 90 && num <= 100)) {
// Do something
}
But you might notice that, if you subtract 1 from num, you'll have the ranges:
10-19, 30-39, 50-59, 70-79, 90-99
In other words, all two-digit numbers whose first digit is odd. Next, you need to come up with a formula that expresses this. You can get the first digit by dividing by 10, and you can test that it's odd by checking for a remainder of 1 when you divide by 2. Putting that all together:
if ((num > 0) && (num <= 100) && (((num - 1) / 10) % 2 == 1)) {
// Do something
}
Given the trade-off between longer but maintainable code and shorter "clever" code, I'd pick longer and clearer every time. At the very least, if you try to be clever, please, please include a comment that explains exactly what you're trying to accomplish.
It helps to assume the next developer to work on the code is armed and knows where you live. :-)
If you are using GCC or any compiler that supports case ranges you can do this, but your code will not be portable.
switch(num)
{
case 11 ... 20:
case 31 ... 40:
case 51 ... 60:
case 71 ... 80:
case 91 ... 100:
// Do something
break;
default:
// Do something else
break;
}
This is for future visitors more so than a beginner. For a more general, algorithm-like solution, you can take a list of starting and ending values and check if a passed value is within one of them:
template<typename It, typename Elem>
bool in_any_interval(It first, It last, const Elem &val) {
return std::any_of(first, last, [&val](const auto &p) {
return p.first <= val && val <= p.second;
});
}
For simplicity, I used a polymorphic lambda (C++14) instead of an explicit pair argument. This should also probably stick to using < and == to be consistent with the standard algorithms, but it works like this as long as Elem has <= defined for it. Anyway, it can be used like this:
std::pair<int, int> intervals[]{
{11, 20}, {31, 40}, {51, 60}, {71, 80}, {91, 100}
};
const int num = 15;
std::cout << in_any_interval(std::begin(intervals), std::end(intervals), num);
There's a live example here.
The first one is easy. You just need to apply the modulo operator to your num value:
if ( ( num % 10 ) == 0)
Since C++ is evaluating every number that is not 0 as true, you could also write:
if ( ! ( num % 10 ) ) // Does not have a residue when divided by 10
For the second one, I think this is cleaner to understand:
The pattern repeats every 20, so you can calculate modulo 20.
All elements you want will be in a row except the ones that are dividable by 20.
To get those too, just use num-1 or better num+19 to avoid dealing with negative numbers.
if ( ( ( num + 19 ) % 20 ) > 9 )
This is assuming the pattern repeats forever, so for 111-120 it would apply again, and so on. Otherwise you need to limit the numbers to 100:
if ( ( ( ( num + 19 ) % 20 ) > 9 ) && ( num <= 100 ) )
With a couple of good comments in the code, it can be written quite concisely and readably.
// Check if it's a multiple of 10
if (num % 10 == 0) { ... }
// Check for whether tens digit is zero or even (1-10, 21-30, ...)
if ((num / 10) % 2 == 0) { ... }
else { ... }
You basically explained the answer yourself, but here's the code just in case.
if((x % 10) == 0) {
// Do this
}
if((x > 10 && x < 21) || (x > 30 && x < 41) || (x > 50 && x < 61) || (x > 70 && x < 81) || (x > 90 && x < 101)) {
// Do this
}
You might be overthinking this.
if (x % 10)
{
.. code for 1..9 ..
} else
{
.. code for 0, 10, 20 etc.
}
The first line if (x % 10) works because (a) a value that is a multiple of 10 calculates as '0', other numbers result in their remainer, (b) a value of 0 in an if is considered false, any other value is true.
Edit:
To toggle back-and-forth in twenties, use the same trick. This time, the pivotal number is 10:
if (((x-1)/10) & 1)
{
.. code for 10, 30, ..
} else
{
.. code for 20, 40, etc.
}
x/10 returns any number from 0 to 9 as 0, 10 to 19 as 1 and so on. Testing on even or odd -- the & 1 -- tells you if it's even or odd. Since your ranges are actually "11 to 20", subtract 1 before testing.
A plea for readability
While you already have some good answers, I would like to recommend a programming technique that will make your code more readable for some future reader - that can be you in six months, a colleague asked to perform a code review, your successor, ...
This is to wrap any "clever" statements into a function that shows exactly (with its name) what it is doing. While there is a miniscule impact on performance (from "function calling overhead") this is truly negligible in a game situation like this.
Along the way you can sanitize your inputs - for example, test for "illegal" values. Thus you might end up with code like this - see how much more readable it is? The "helper functions" can be hidden away somewhere (the don't need to be in the main module: it is clear from their name what they do):
#include <stdio.h>
enum {NO, YES, WINNER};
enum {OUT_OF_RANGE=-1, ODD, EVEN};
int notInRange(int square) {
return(square < 1 || square > 100)?YES:NO;
}
int isEndOfRow(int square) {
if (notInRange(square)) return OUT_OF_RANGE;
if (square == 100) return WINNER; // I am making this up...
return (square % 10 == 0)? YES:NO;
}
int rowType(unsigned int square) {
// return 1 if square is in odd row (going to the right)
// and 0 if square is in even row (going to the left)
if (notInRange(square)) return OUT_OF_RANGE; // trap this error
int rowNum = (square - 1) / 10;
return (rowNum % 2 == 0) ? ODD:EVEN; // return 0 (ODD) for 1-10, 21-30 etc.
// and 1 (EVEN) for 11-20, 31-40, ...
}
int main(void) {
int a = 12;
int rt;
rt = rowType(a); // this replaces your obscure if statement
// and here is how you handle the possible return values:
switch(rt) {
case ODD:
printf("It is an odd row\n");
break;
case EVEN:
printf("It is an even row\n");
break;
case OUT_OF_RANGE:
printf("It is out of range\n");
break;
default:
printf("Unexpected return value from rowType!\n");
}
if(isEndOfRow(10)==YES) printf("10 is at the end of a row\n");
if(isEndOfRow(100)==WINNER) printf("We have a winner!\n");
}
For the first one:
if (x % 10 == 0)
will apply to:
10, 20, 30, .. 100 .. 1000 ...
For the second one:
if (((x-1) / 10) % 2 == 1)
will apply for:
11-20, 31-40, 51-60, ..
We basically first do x-1 to get:
10-19, 30-39, 50-59, ..
Then we divide them by 10 to get:
1, 3, 5, ..
So we check if this result is odd.
As others have pointed out, making the conditions more concise won't speed up the compilation or the execution, and it doesn't necessarily help with readability either.
It can help in making your program more flexible, in case you decide later that you want a toddler's version of the game on a 6 x 6 board, or an advanced version (that you can play all night long) on a 40 x 50 board.
So I would code it as follows:
// What is the size of the game board?
#define ROWS 10
#define COLUMNS 10
// The numbers of the squares go from 1 (bottom-left) to (ROWS * COLUMNS)
// (top-left if ROWS is even, or top-right if ROWS is odd)
#define firstSquare 1
#define lastSquare (ROWS * COLUMNS)
// We haven't started until we roll the die and move onto the first square,
// so there is an imaginary 'square zero'
#define notStarted(num) (num == 0)
// and we only win when we land exactly on the last square
#define finished(num) (num == lastSquare)
#define overShot(num) (num > lastSquare)
// We will number our rows from 1 to ROWS, and our columns from 1 to COLUMNS
// (apologies to C fanatics who believe the world should be zero-based, which would
// have simplified these expressions)
#define getRow(num) (((num - 1) / COLUMNS) + 1)
#define getCol(num) (((num - 1) % COLUMNS) + 1)
// What direction are we moving in?
// On rows 1, 3, 5, etc. we go from left to right
#define isLeftToRightRow(num) ((getRow(num) % 2) == 1)
// On rows 2, 4, 6, etc. we go from right to left
#define isRightToLeftRow(num) ((getRow(num) % 2) == 0)
// Are we on the last square in the row?
#define isLastInRow(num) (getCol(num) == COLUMNS)
// And finally we can get onto the code
if (notStarted(mySquare))
{
// Some code for when we haven't got our piece on the board yet
}
else
{
if (isLastInRow(mySquare))
{
// Some code for when we're on the last square in a row
}
if (isRightToLeftRow(mySquare))
{
// Some code for when we're travelling from right to left
}
else
{
// Some code for when we're travelling from left to right
}
}
Yes, it's verbose, but it makes it clear exactly what's happening on the game board.
If I was developing this game to display on a phone or tablet, I'd make ROWS and COLUMNS variables instead of constants, so they can be set dynamically (at the start of a game) to match the screen size and orientation.
I'd also allow the screen orientation to be changed at any time, mid-game - all you need to do is switch the values of ROWS and COLUMNS, while leaving everything else (the current square number that each player is on, and the start/end squares of all the snakes and ladders) unchanged.
Then you 'just' have to draw the board nicely, and write code for your animations (I assume that was the purpose of your if statements) ...
You can try the following:
// Multiple of 10
if ((num % 10) == 0)
{
// Do something
}
else if (((num / 10) % 2) != 0)
{
// 11-20, 31-40, 51-60, 71-80, 91-100
}
else
{
// Other case
}
I know that this question has so many answers, but I will thrown mine here anyway...
Taken from Steve McConnell's Code Complete, 2nd Edition:
"Stair-Step Access Tables:
Yet another kind of table access is the stair-step method. This access method isn’t as direct as an index structure, but it doesn’t waste as much data space. The general idea of stair-step structures, illustrated in Figure 18-5, is that entries in a table are valid for ranges of data rather than for distinct data points.
Figure 18-5 The stair-step approach categorizes each entry by determining the level at which it hits a “staircase.” The “step” it hits determines its category.
For example, if you’re writing a grading program, the “B” entry range might be from 75 percent to 90 percent. Here’s a range of grades you might have to program someday:
To use the stair-step method, you put the upper end of each range into a table and then write a loop to check a score against the upper end of each range. When you find the point at which the score first exceeds the top of a range, you know what the grade is. With the stair-step technique, you have to be careful to handle the endpoints of the ranges properly. Here’s the code in Visual Basic that assigns grades to a group of students based on this example:
Although this is a simple example, you can easily generalize it to handle multiple students, multiple grading schemes (for example, different grades for different point levels on different assignments), and changes in the grading scheme."
Code Complete, 2nd Edition, pages 426 - 428 (Chapter 18).
The keypad is broken so the input numbers 1, 4, and 7 aren't working. In turn the computer outputs the next lowest and next highest number where 1, 4, and 7 are none of the digits.
My goal is to check out the digits and output true using a boolean function and then output the next highest number and next lowest number. I'm pretty sure I did most of what I need to do, but it isn't working out.
I have inputted the number 444, and the results that came out were 443, and 445.
Thank you for your help.
#include <iostream>
#include <conio.h>
#include <cmath>
using namespace std;
bool containDigit(int number, int digit);
int main()
{
int number, digit, lowNum, highNum;
cout<<"Enter a number between 1 and 999 for the oven temperature: ";
cin>>number;
//1st digit
digit = number / 100;
containDigit(number, digit);
if (containDigit(number, digit) == true)
{
number = number - 100;
}
//2nd digit
digit = (number / 10) % 10;
containDigit(number, digit);
if (containDigit(number, digit) == true)
{
number = number - 10;
}
//3rd Digit
digit = number % 10;
containDigit(number, digit);
if (containDigit(number, digit) == true)
{
number = number - 1;
}
cout<<number<<endl;
getche();
return 0;
}
bool containDigit(int number, int digit)
{
if ((digit == 1) || (digit == 4) || (digit == 7))
{
return true;
}
else
{
return 0;
}
}
The bug is in containDigit function. Try this:
bool containDigit(int number, int digit) {
if(digit == 1 || digit == 4 || digit == 7) return true;
return false;
}
You must use == instead of =.
Also you actually don't need number argument there.
Also there can be done several optimizations. Please look at it yourself (it's your homework) and think about repeated code.
Since this looks like homework, I will refrain from doing it for you and give you these hints:
It looks like you're not really clear on what "1st digit" is. Is it the first one from the left (hundreds) or the right (ones)? Look at your code and tell yourself how each portion of it would answer my question.
Is it ever possible for lowNum or highNum to have more than one digit different than number with your code as it is? How? Where are lowNum and highNum changed, and how?
Also, to expand on what #Al Kepp has said: When you have a function like that, try to test it with some very simple inputs rather than straight out assuming it works. This is called (or is similar to) "unit testing", which dictates that you divide your program into simple, independent units and test them separately. A simple call like containDigit(999, 4) returning true would've rang warning bells.
And speaking of warnings, always, always compile with as many of them as you can stand. (e.g. -Wall for gcc) Doing such might've warned you of the fact that you're not using the parameter number inside containDigit at all.
Your function containDigit has two problems:
It shouldn't need to receive the variable "number" as it doesn't use it
You want to compare with == not =
I am trying to make a program generating random numbers until it finds a predefined set of numbers (eg. if I had a set of my 5 favourite numbers, how many times would I need to play for the computer to randomly find the same numbers). I have written a simple program but don't understand the outcome which seems to be slightly unrelated to what I expected, for example the outcome does not necessarily contain all of the predefined numbers sometimes it does (and even that doesn't stop the loop from running). I think that the problem lies in the logical operator '&&' but am not sure. Here is the code:
const int one = 1;
const int two = 2;
const int three = 3;
using namespace std;
int main()
{
int first, second, third;
int i = 0;
time_t seconds;
time(&seconds);
srand ((unsigned int) seconds);
do
{
first = rand() % 10 + 1;
second = rand() % 10 + 1;
third = rand() % 10 + 1;
i++;
cout << first<<","<<second<<","<<third<< endl;
cout <<i<<endl;
} while (first != one && second != two && third != three);
return 0;
}
and here is out of the possible outcomes:
3,10,4
1 // itineration variable
7,10,4
2
4,4,6
3
3,5,6
4
7,1,8
5
5,4,2
6
2,5,7
7
2,4,7
8
8,4,9
9
7,4,4
10
8,6,5
11
3,2,7
12
I have also noticed that If I use the || operator instead of && the loop will execute until it finds the exact numbers respecting the order in which the variables were set (here: 1,2,3). This is better however what shall I do make the loop stop even if the order is not the same, only the numbers? Thanks for your answers and help.
The issue is here in your condition:
} while (first != one && second != two && third != three);
You continue while none of them is equal. But once at least one of them is equal, you stop/leave the loop.
To fix this, use logical or (||) rather than a logical and (&&) to link the tests:
} while (first != one || second != two || third != three);
Now it will continue as long as any of them doesn't match.
Edit - for a more advanced comparison:
I'll be using a simple macro to make it easier to read:
#define isoneof(x,a,b,c) ((x) == (a) || (x) == (b) || (x) == (c))
Note that there are different approaches you could use.
} while(!isoneof(first, one, two, three) || !isoneof(second, one, two, three) || !isoneof(third, one, two, three))
You have a mistake in your logical condition: it means "while all numbers are not equal". To break this condition, it is enough for one pair to become equal.
You needed to construct a different condition - either put "not" in front of it
!(first==one && second==two && third==three)
or convert using De Morgan's law:
first!=one || second!=two || third!=three