I'm doing a homework problem where I have two take input from a user in the form of two dynamic char arrays (max of 100 characters each) and returning their sum.
I'm struggling with coming up with a sum function that works correctly when the two numbers are of different length or when the answer is less than 100 digits. When the numbers are of different length, they get added as if they were the same (e.g. 100 + 1000 becomes 1000+1000). When the result is less than 100 digits, the full arrays is printed anyway (so there are dozens of trailing zeros). (EDIT: Fixed, see below).
I know that there is no way to tell the actual size of a dynamic array, and I can't figure out any way to place some sort of sentinel value that stops the program from processing farther. I'm not allowed to use vectors or traditional arrays, which would give me a clear path to the solution. EDIT: This has been fixed by checking for '\0'.
I know SO doesn't want to do people's homework for them (nor am I asking that), but I do need some guidance as to how I can solve this problem. I've been working for hours and still can't think of a solution.
My program is as follows:
#include <iostream>
#include <algorithm>
int* sum(char*, char*);
int main() {
char * arr = new char[100];
char * arr2 = new char[100];
std::cout << "Enter value 1: ";
std::cin >> arr;
std::cout << "Enter value 2: ";
std::cin >> arr2;
int * result = sum(arr, arr2);
std::cout << "Result: ";
for (int i = 0; i < 100 && result[i] != '\0'; i++) {
std::cout << result[i];
}
std::cout << std::endl;
return 0;
}
int* sum(char * num1, char* num2) {
std::reverse(num1, num1 + 100);
std::reverse(num2, num2 + 100);
bool carryOver = false;
int* retarr = new int[100]; //Array to return to user
for (int i = 0; i < 100; i++) {
//Numerical value is char - 48, unless
//char value is zero, then int val is zero
int val1 = std::max(num1[i] - 48, 0);
int val2 = std::max(num2[i] - 48, 0);
int carry = (carryOver)? 1 : 0;
carryOver = false; //Reset carryOver var
int t = val1 + val2 + carry;
if (t >= 10) {
t = t % 10;
carryOver = true;
}
retarr[99 - i] = t;
}
return retarr;
}
Related
I have this code here and I'm trying to do decimal to hexadecimal conversion without using arrays. It is working pretty much but it gives me wrong answers for values greater than 1000. What am I doing wrong? are there any counter solutions? kindly can anyone give suggestions how to improve this code.
for(int i = num; i > 0; i = i/16)
{
temp = i % 16;
(temp < 10) ? temp = temp + 48 : temp = temp + 55;
num = num * 100 + temp;
}
cout<<"Hexadecimal = ";
for(int j = num; j > 0; j = j/100)
{
ch = j % 100;
cout << ch;
}
There's a couple of errors in the code. But elements of the approach are clear.
This line sort of works:
(temp < 10) ? temp = temp + 48 : temp = temp + 55;
But is confusing because it's using 48 and 55 as magic numbers!
It also may lead to overflow.
It's repacking hex digits as decimal character values.
It's also unconventional to use ?: in that way.
Half the trick of radix output is that each digit is n%r followed by n/r but the digits come out 'backwards' for conventional left-right output.
This code reverses the hex digits into another variable then reads them out.
So it avoids any overflow risks.
It works with an unsigned value for clarity and a lack of any specification as how to handle negative values.
#include <iostream>
void hex(unsigned num){
unsigned val=num;
const unsigned radix=16;
unsigned temp=0;
while(val!=0){
temp=temp*radix+val%radix;
val/=radix;
}
do{
unsigned digit=temp%16;
char c=digit<10?'0'+digit:'A'+(digit-10);
std::cout << c;
temp/=16;
}while(temp!=0);
std::cout << '\n';
}
int main(void) {
hex(0x23U);
hex(0x0U);
hex(0x7U);
hex(0xABCDU);
return 0;
}
Expected Output:
23
0
8
ABCD
Arguably it's more obvious what is going on if the middle lines of the first loop are:
while(val!=0){
temp=(temp<<4)+(val&0b1111);
val=val>>4;
}
That exposes that we're building temp as blocks of 4 bits of val in reverse order.
So the value 0x89AB with be 0xBA98 and is then output in reverse.
I've not done that because bitwise operations may not be familiar.
It's a double reverse!
The mapping into characters is done at output to avoid overflow issues.
Using character literals like 0 instead of integer literals like 44 is more readable and makes the intention clearer.
So here's a single loop version of the solution to the problem which should work for any sized integer:-
#include <iostream>
#include <string>
using namespace std;
void main(int argc, char *argv[1])
{
try
{
unsigned
value = argc == 2 ? stoi(argv[1]) : 64;
for (unsigned i = numeric_limits<unsigned>::digits; i > 0; i -= 4)
{
unsigned
digit = (value >> (i - 4)) & 0xf;
cout << (char)((digit < 10) ? digit + 48 : digit + 55);
}
cout << endl;
}
catch (exception e)
{
cout << e.what() << endl;
}
}
There is a mistake in your code, in the second loop you should exit when j > original num, or set the cumulative sum with non-zero value, I also changed the cumulative num to be long int, rest should be fine.
void tohex(int value){
long int num = 1;
char ch = 0;
int temp = 0;
for(int i = value; i > 0; i = i/16)
{
temp = i % 16;
(temp < 10) ? temp = temp + 48 : temp = temp + 55;
num = num * 100 + temp;
}
cout<<"Hexadecimal = ";
for(long int j = num; j > 99; j = j/100)
{
ch = j % 100;
cout << ch;
}
cout << endl;
}
If this is a homework assignment, it is probably related to the chapter on Recursivity. See a solution below. To understand it, you need to know
what a lookup table is
what recursion is
how to convert a number from one base to another iteratively
basic io
void hex_out(unsigned n)
{
static const char* t = "0123456789abcdef"; // lookup table
if (!n) // recursion break condition
return;
hex_out(n / 16);
std::cout << t[n % 16];
}
Note that there is no output for zero. This can be solved simply by calling the recursive function from a second function.
You can also add a second parameter, base, so that you can call the function this way:
b_out(123, 10); // decimal
b_out(123, 2); // binary
b_out(123, 8); // octal
#include <iostream>
#include<ctime>
#include<cstdlib>
#include<string>
#include<cmath>
using namespace std;
int main()
{
bool cont = false;
string str;
int num, num2;
cin >> str >> num;
int arr[10];
int a = pow(10, num);
int b = pow(10, (num - 1));
srand(static_cast<int>(time(NULL)));
do {
num2 = rand() % (a - b) + b;
int r;
int i = 0;
int cpy = num2;
while (cpy != 0) {
r = cpy % 10;
arr[i] = r;
i++;
cpy = cpy / 10;
}
for (int m = 0; m < num; m++)
{
for (int j = 0; j < m; j++) {
if (m != j) {
if (arr[m] == arr[j]) {
break;
}
else {
cont = true;
}
}
}
}
cout << num2 << endl;
} while (!cont);
return 0;
}
I want to take a number from the user and produce such a random number.
For example, if the user entered 8, an 8-digit random number.This number must be unique, so each number must be different from each other,for example:
user enter 5
random number=11225(invalid so take new number)
random number =12345(valid so output)
To do this, I divided the number into its digits and threw it into the array and checked whether it was unique. The Program takes random numbers from the user and throws them into the array.It's all right until this part.But my function to check if this number is unique using the for loop does not work.
Because you need your digits to be unique, it's easier to guarantee the uniqueness up front and then mix it around. The problem-solving principle at play here is to start where you are the most constrained. For you, it's repeating digits, so we ensure that will never happen. It's a lot easier than verifying if we did or not.
This code example will print the unique number to the screen. If you need to actually store it in an int, then there's extra work to be done.
#include <algorithm>
#include <iostream>
#include <numeric>
#include <random>
#include <vector>
int main() {
std::vector<int> digits(10);
std::iota(digits.begin(), digits.end(), 0);
std::shuffle(digits.begin(), digits.end(), std::mt19937(std::random_device{}()));
int x;
std::cout << "Number: ";
std::cin >> x;
for (auto it = digits.begin(); it != digits.begin() + x; ++it) {
std::cout << *it;
}
std::cout << '\n';
}
A few sample runs:
Number: 7
6253079
Number: 3
893
Number: 6
170352
The vector digits holds the digits 0-9, each only appearing once. I then shuffle them around. And based on the number that's input by the user, I then print the first x single digits.
The one downside to this code is that it's possible for 0 to be the first digit, and that may or may not fit in with your rules. If it doesn't, you'd be restricted to a 9-digit number, and the starting value in std::iota would be 1.
First I'm going to recommend you make better choices in naming your variables. You do this:
bool cont = false;
string str;
int num, num2;
cin >> str >> num;
What are num and num2? Give them better names. Why are you cin >> str? I can't even see how you're using it later. But I presume that num is the number of digits you want.
It's also not at all clear what you're using a and b for. Now, I presume this next bit of code is an attempt to create a number. If you're going to blindly try and then when done, see if it's okay, why are you making this so complicated. Instead of this:
num2 = rand() % (a - b) + b;
int r;
int i = 0;
int cpy = num2;
while (cpy != 0) {
r = cpy % 10;
arr[i] = r;
i++;
cpy = cpy / 10;
}
You can do this:
for(int index = 0; index < numberOfDesiredDigits; ++index) {
arr[index] = rand() % 10;
}
I'm not sure why you went for so much more complicated.
I think this is your code where you validate:
// So you iterate the entire array
for (int m = 0; m < num; m++)
{
// And then you check all the values less than the current spot.
for (int j = 0; j < m; j++) {
// This if not needed as j is always less than m.
if (m != j) {
// This if-else is flawed
if (arr[m] == arr[j]) {
break;
}
else {
cont = true;
}
}
}
}
You're trying to make sure you have no duplicates. You're setting cont == true if the first and second digit are different, and you're breaking as soon as you find a dup. I think you need to rethink that.
bool areAllUnique = true;
for (int m = 1; allAreUnique && m < num; m++) {
for (int j = 0; allAreUnique && j < m; ++j) {
allAreUnique = arr[m] != arr[j];
}
}
As soon as we encounter a duplicate, allAreUnique becomes false and we break out of both for-loops.
Then you can check it.
Note that I also start the first loop at 1 instead of 0. There's no reason to start the outer loop at 0, because then the inner loop becomes a no-op.
A better way is to keep a set of valid digits -- initialized with 1 to 10. Then grab a random number within the size of the set and grabbing the n'th digit from the set and remove it from the set. You'll get a valid result the first time.
#include<iostream>
int fastFibonacci(int n)
{
int numbers[n+2]; // int numbers[n].
numbers[0] = 0;
numbers[1] = 1;
for (int i = 2; i <= n; i++)
{
numbers[i] = numbers[i - 1] + numbers[i - 2];
}
return numbers[n];
}
int main() {
int n;
std::cout << "Enter a Number";
std::cin >> n;
int result = fastFibonacci(n);
std::cout << result << "\n";
return 0;
}
in this code when i enter input 0 or 1 get correct answer. But the problem is that when i replace int numbers[n+2]; with the commented part it start giving me wrong answer when input is 0 or 1. why? anyone please explain me.
In this function
int fastFibonacci(int n)
{
int numbers[n+2]; // int numbers[n].
numbers[0] = 0;
numbers[1] = 1;
for (int i = 2; i <= n; i++)
{
numbers[i] = numbers[i - 1] + numbers[i - 2];
}
return numbers[n];
}
there is used a variable length array with n + 2 elements declared in this line
int numbers[n+2]; // int numbers[n].
Variable length arrays is not a standard C++ feature. It can be implemented as own language extension of a C++ compiler.
Using the variable length array makes the function very unsafe because there can occur a stack overflow.
As within the function there is explicitly used two elements of the array
numbers[0] = 0;
numbers[1] = 1;
then the array shall have at least two elements even when the parameter has a value less than 2.
To calculate the n-th Fibonacci number there is no need to declare an array of such a size.
Apart from this the function argument shall have an unsigned integer type. Otherwise the function can invoke undefined behavior if the user passes a negative number.
Also for big values of n there can be an integer overflow for the type int.
The function can be implemented in various ways.
Here is one of possible its implementations.
#include <iostream>
#include <functional>
unsigned long long fibonacci( unsigned int n )
{
unsigned long long a[] = { 0, 1 };
while ( n-- )
{
a[1] += std::exchange( a[0], a[1] );
}
return a[0];
}
int main()
{
const unsigned int N = 10;
for ( unsigned int i = 0; i < N; i++ )
{
std::cout << i << ": " << fibonacci( i ) << '\n';
}
return 0;
}
The program output is
0: 0
1: 1
2: 1
3: 2
4: 3
5: 5
6: 8
7: 13
8: 21
9: 34
int numbers[n+2]; is the declaration of an array of ints with space for n + 2 ints, this is a variable lenght array and is not part of C++ standard, though some compilers allow it it's not somenthing you should use.
If you need a variable lenght array use std::vector.
With int numbers[n+2]; if n is equal to 0 you still have space for 2 ints, if you have int numbers[n]; the array will have space for 0 ints, so the code will fail because you are trying to access memory that does not exist with numbers[0] and numbers[1].
There are several good ways to implement the Fibonacci sequence, in the site you can find many questions regarding this matter in several programming languages, here is one of them Fibonacci series in C++
Edit
So I've seen your comments about using a vector, for making the sequence you wouldn't need the vector just two variables to store the two numbers to add, to store the sequence in a vactor, you can do somenthing like:
#include <iostream>
#include <vector>
#include <iomanip>
//passing the vector by reference
void fastFibonacci(unsigned long long n, std::vector<unsigned long long>& sequence) {
unsigned long long first = 0;
unsigned long long second = 1;
sequence.push_back(first); //add first values to the vector
sequence.push_back(second); //add first values to the vector
for (unsigned long long i = 0, value = 0; i < n && value <= LLONG_MAX ; ++i) {
value = first + second;
first = second;
second = value;
sequence.push_back(value); //adding values to the vector
}
}
int main() {
unsigned long long limit; //number of values in the sequence
int num = 1;
std::vector<unsigned long long> sequence; //container for the sequence
std::cout << "Enter upper limit: ";
std::cin >> limit;
fastFibonacci(limit, sequence);
//print the sequence in a range based loop formatted with <iomanip> library
for(auto& i : sequence){
std::cout << std::setw(4) << std::left << num++ << " " << i << std::endl;
}
return 0;
}
If you want to print just one of the numbers in the sequence, just use, for instance:
std::cout << sequence[10];
Instead of the whole vector.
The code you post in the comment to the other answer won't work because the access to the vector is out of bounds in numbers[i] = numbers[i - 1] + numbers[i - 2];, if for instance i = 5, your vector only has 2 nodes but you are accessing the 6th node numbers[5].
I have written a program below that converts a string to an int and then converts the decimal number to hexadecimal. I'm struggling to check if the hexadecimal consists only of these characters A, B, C, D, E, F, 1, 0. If so set a flag to true or false.
#include<iostream>
#include <stdlib.h>
#include <string>
#include <sstream>
string solution(string &S){
int n = stoi(S);
int answer;
cout << "stoi(\"" << S << "\") is "
<< n << '\n';
//decToHexa(myint);
// char array to store hexadecimal number
string hexaDeciNum[100];
// counter for hexadecimal number array
int i = 0;
while(n!=0)
{
// temporary variable to store remainder
int temp = 0;
// storing remainder in temp variable.
temp = n % 16;
// check if temp < 10
if(temp < 10)
{
hexaDeciNum[i] = temp + 48;
i++;
}
else
{
hexaDeciNum[i] = temp + 55;
i++;
}
n = n/16;
}
// printing hexadecimal number array in reverse order
for(int j=i-1; j>=0; j--){
cout << hexaDeciNum[j] << "\n";
return "";
}
int main() {
string word = "300";
cout << solution(word);
return 0;
}
OK, it is not the exact answer to what you are asking for, but it is a valuable alternative approach for the entire problem of conversion:
char letter(unsigned int digit)
{
return "0123456789abcdefg"[digit];
// alternatively upper case letters, if you prefer...
}
Now you don't have to differenciate... You can even use this approach for inverse conversion:
int digit(char letter)
{
int d = -1; // invalid letter...
char const* letters = "0123456789abcdefABCDEF";
char* l = strchr(letters, letter);
if(l)
{
d = l - letters;
if(d >= 16)
d -= 6;
}
// alternatively upper case letters, if you prefer...
}
Another advantage: This works even on these strange character sets where digits and letters are not necessarily grouped into ranges (e. g. EBCDIC).
I am writing code to get the last digit of very large fibonacci numbers such as fib(239), etc.. I am using strings to store the numbers, grabbing the individual chars from end to beginning and then converting them to int and than storing the values back into another string. I have not been able to test what I have written because my program keeps abruptly closing after the std::cin >> n; line.
Here is what I have so far.
#include <iostream>
#include <string>
using std::cin;
using std::cout;
using namespace std;
char get_fibonacci_last_digit_naive(int n) {
cout << "in func";
if (n <= 1)
return (char)n;
string previous= "0";
string current= "1";
for (int i = 0; i < n - 1; ++i) {
//long long tmp_previous = previous;
string tmp_previous= previous;
previous = current;
//current = tmp_previous + current; // could also use previous instead of current
// for with the current length of the longest of the two strings
//iterates from the end of the string to the front
for (int j=current.length(); j>=0; --j) {
// grab consectutive positions in the strings & convert them to integers
int t;
if (tmp_previous.at(j) == '\0')
// tmp_previous is empty use 0 instead
t=0;
else
t = stoi((string&)(tmp_previous.at(j)));
int c = stoi((string&)(current.at(j)));
// add the integers together
int valueAtJ= t+c;
// store the value into the equivalent position in current
current.at(j) = (char)(valueAtJ);
}
cout << current << ":current value";
}
return current[current.length()-1];
}
int main() {
int n;
std::cin >> n;
//char& c = get_fibonacci_last_digit_naive(n); // reference to a local variable returned WARNING
// http://stackoverflow.com/questions/4643713/c-returning-reference-to-local-variable
cout << "before call";
char c = get_fibonacci_last_digit_naive(n);
std::cout << c << '\n';
return 0;
}
The output is consistently the same. No matter what I enter for n, the output is always the same. This is the line I used to run the code and its output.
$ g++ -pipe -O2 -std=c++14 fibonacci_last_digit.cpp -lm
$ ./a.exe
10
There is a newline after the 10 and the 10 is what I input for n.
I appreciate any help. And happy holidays!
I'm posting this because your understanding of the problem seems to be taking a backseat to the choice of solution you're attempting to deploy. This is an example of an XY Problem, a problem where the choice of solution method and problems or roadblocks with its implementation obfuscates the actual problem you're trying to solve.
You are trying to calculate the final digit of the Nth Fibonacci number, where N could be gregarious. The basic understanding of the fibonacci sequence tells you that
fib(0) = 0
fib(1) = 1
fib(n) = fib(n-1) + fib(n-2), for all n larger than 1.
The iterative solution to solving fib(N) for its value would be:
unsigned fib(unsigned n)
{
if (n <= 1)
return n;
unsigned previous = 0;
unsigned current = 1;
for (int i=1; i<n; ++i)
{
unsigned value = previous + current;
previous = current;
current = value;
}
return current;
}
which is all well and good, but will obviously overflow once N causes an overflow of the storage capabilities of our chosen data type (in the above case, unsigned on most 32bit platforms will overflow after a mere 47 iterations).
But we don't need the actual fib values for each iteration. We only need the last digit of each iteration. Well, the base-10 last-digit is easy enough to get from any unsigned value. For our example, simply replace this:
current = value;
with this:
current = value % 10;
giving us a near-identical algorithm, but one that only "remembers" the last digit on each iteration:
unsigned fib_last_digit(unsigned n)
{
if (n <= 1)
return n;
unsigned previous = 0;
unsigned current = 1;
for (int i=1; i<n; ++i)
{
unsigned value = previous + current;
previous = current;
current = value % 10; // HERE
}
return current;
}
Now current always holds the single last digit of the prior sum, whether that prior sum exceeded 10 or not really isn't relevant to us. Once we have that the next iteration can use it to calculate the sum of two single positive digits, which cannot exceed 18, and again, we only need the last digit from that for the next iteration, etc.. This continues until we iterate however many times requested, and when finished, the final answer will present itself.
Validation
We know the first 20 or so fibonacci numbers look like this, run through fib:
0:0
1:1
2:1
3:2
4:3
5:5
6:8
7:13
8:21
9:34
10:55
11:89
12:144
13:233
14:377
15:610
16:987
17:1597
18:2584
19:4181
20:6765
Here's what we get when we run the algorithm through fib_last_digit instead:
0:0
1:1
2:1
3:2
4:3
5:5
6:8
7:3
8:1
9:4
10:5
11:9
12:4
13:3
14:7
15:0
16:7
17:7
18:4
19:1
20:5
That should give you a budding sense of confidence this is likely the algorithm you seek, and you can forego the string manipulations entirely.
Running this code on a Mac I get:
libc++abi.dylib: terminating with uncaught exception of type std::out_of_range: basic_string before callin funcAbort trap: 6
The most obvious problem with the code itself is in the following line:
for (int j=current.length(); j>=0; --j) {
Reasons:
If you are doing things like current.at(j), this will crash immediately. For example, the string "blah" has length 4, but there is no character at position 4.
The length of tmp_previous may be different from current. Calling tmp_previous.at(j) will crash when you go from 8 to 13 for example.
Additionally, as others have pointed out, if the the only thing you're interested in is the last digit, you do not need to go through the trouble of looping through every digit of every number. The trick here is to only remember the last digit of previous and current, so large numbers are never a problem and you don't have to do things like stoi.
As an alternative to a previous answer would be the string addition.
I tested it with the fibonacci number of 100000 and it works fine in just a few seconds. Working only with the last digit solves your problem for even larger numbers for sure. for all of you requiring the fibonacci number as well, here an algorithm:
std::string str_add(std::string a, std::string b)
{
// http://ideone.com/o7wLTt
size_t n = max(a.size(), b.size());
if (n > a.size()) {
a = string(n-a.size(), '0') + a;
}
if (n > b.size()) {
b = string(n-b.size(), '0') + b;
}
string result(n + 1, '0');
char carry = 0;
std::transform(a.rbegin(), a.rend(), b.rbegin(), result.rbegin(), [&carry](char x, char y)
{
char z = (x - '0') + (y - '0') + carry;
if (z > 9) {
carry = 1;
z -= 10;
} else {
carry = 0;
}
return z + '0';
});
result[0] = carry + '0';
n = result.find_first_not_of("0");
if (n != string::npos) {
result = result.substr(n);
}
return result;
}
std::string str_fib(size_t i)
{
std::string n1 = "0";
std::string n2 = "1";
for (size_t idx = 0; idx < i; ++idx) {
const std::string f = str_add(n1, n2);
n1 = n2;
n2 = f;
}
return n1;
}
int main() {
const size_t i = 100000;
const std::string f = str_fib(i);
if (!f.empty()) {
std::cout << "fibonacci of " << i << " = " << f << " | last digit: " << f[f.size() - 1] << std::endl;
}
std::cin.sync(); std::cin.get();
return 0;
}
Try it with first calculating the fibonacci number and then converting the int to a std::string using std::to_string(). in the following you can extract the last digit using the [] operator on the last index.
int fib(int i)
{
int number = 1;
if (i > 2) {
number = fib(i - 1) + fib(i - 2);
}
return number;
}
int main() {
const int i = 10;
const int f = fib(i);
const std::string s = std::to_string(f);
if (!s.empty()) {
std::cout << "fibonacci of " << i << " = " << f << " | last digit: " << s[s.size() - 1] << std::endl;
}
std::cin.sync(); std::cin.get();
return 0;
}
Avoid duplicates of the using keyword using.
Also consider switching from int to long or long long when your numbers get bigger. Since the fibonacci numbers are positive, also use unsigned.