I'm studying C++ by 2 months using the book : Programming principles and practice using C++. Now I'm reading the chapter about errors, and in a section the author speaks of logic errors. Before using a program as an example, and then a revised version to understand the error. This is the first program :
#include "std_lib_facilities.h"
// find the highest, lowest and averega temperature
int main()
{
vector<double> temps;
for (double temp; cin >> temp;)
temps.push_back(temp);
double sum = 0;
double high_temp = 0;
double low_temp = 0;
for (double x : temps)
{
if (x > high_temp) high_temp = x;
if (x < low_temp) low_temp = x;
sum += x;
}
cout << "Highest temperature : " << high_temp << '\n';
cout << "Lowest temperature : " << low_temp << '\n';
cout << "Average temperature : " << sum / temps.size() << '\n';
}
As you can see if I enter, for example, a set of temperatures relating to the month of August I will get wrong ouput results because I will enter just positive values but low_temp will remain 0.0 unless one of the temperatures in the data was below zero (impossible in summer !).
So the author revised this program :
#include "std_lib_facilities.h"
int main()
{
vector<double> temps;
double high_temp = -1000; // initialize to impossibly low
double low_temp = 1000; // initialize to impossibly high
double sum = 0;
int no_of_temps = 0;
for (double temp; cin >> temp;) {
++no_of_temps;
sum += temp;
if (temp > high_temp) high_temp = temp;
if (temp < low_temp) low_temp = temp;
}
cout << "Highest temperature : " << high_temp << '\n';
cout << "Lowest temperature : " << low_temp << '\n';
cout << "Average temperature : " << sum / no_of_temps<< '\n';
}
My problem lies in the exercise that the author asks me to do :
Look it up. Check some information sources to pick good values for the min_temp("the minimum temperaure") and max_temp("the maximum temperature") constants of our program. Those values will determine the usefulness of our program.
What does you mean the author with this exercise? the program still needs some improvements in your opinion? What values you would give to min_temp and max_temp ? What are the problems related to the solution used to write such a program ?
You should start with such constants such that the first comparison will always succeed. Picking +/-1000 is OK, but then you're artificially limiting yourself when you don't have to. A better solution might be to pick constants that are definitely at the extremes:
double high_temp = -std::numeric_limits<double>::infinity();
double low_temp = std::numeric_limits<double>::infinity();
Any temperature you enter will be higher than -inf and lower than inf, so that comparison will succeed and do the right thing.
Related
This question already has answers here:
What is the behavior of integer division?
(6 answers)
Closed 1 year ago.
Hi guys I'm rather new to programming and working my way through Stroustrup's "Programming, Principles and Practice Using C++" and I've come to a complete standstill at the end of Chapter 3 with an exercise asking you to write a piece of code that does a number of calculations involving 2 numbers which includes finding the ratio of the numbers. Unfortunately this hasn't been covered at all in the book and I'm tearing my hair out trying to figure it out by myself, only able to find examples of code way to advanced for my small little brain.
The code I have at the moment is:
double ratio;
if (val2 > val1)
ratio = (val2 / val1);
if (val2 < val1)
ratio = (val1 / val2);
cout << "The ratio of " << val1 << " and " << val2 << " is 1:" << ratio << '\n';
which works fine for numbers that equate to a whole ratio (e.g. 100 and 25) however despite me setting the variable "ratio" as a double it removes any decimals from the answer in cases of non whole number ratios. Can anyone tell me where I'm going wrong?
When dividing integers the result is integer (integer arithmetics is used):
11 / 2 == 5
11 % 2 == 1 /* remainder */
and when dividing floating point values the result is floating point as well:
11.0 / 2 == 5.5
11 / 2.0 == 5.5
((double) 11) / 2 == 5.5
In your case
double ratio = (val2 / val1);
you have an integer division and only after the disvison performed the outcome of it is cast to double. You can either declare val2 and val1 as double:
double val1;
double val2;
or cast at least one argument of the ratio to double:
double ratio = ((double)val2) / val1;
The fact that result type is double doesn't matter if the original division is performed on integral types (truncating the decimal part).
So to solve your problem, either:
Use a floating point type for the input numbers as well
Cast one of the numbers to a floating point type before division
I did the whole problem from Stroustrup's "Programming, Principles and Practice Using C++. Here is the codes although no comments.
int main()
{
/** --------Numbers-----*/
int val1;
int val2;
double largest; //I'll store here the largest value
double smallest; //I'll store here the smallest value
cout<< " Enter two Numbers to play with\n";
while(cin>> val1>>val2){
if(val1<val2){
cout<< "smallest: "<<val1<<endl;
cout<< "largest: "<<val2<<endl;
//If the above argument succeeds, largest and smallest will get their values
largest=val2;
smallest=val1;}
if(val1>val2){
cout<< "smallest: "<<val2<<endl;
cout<< "largest: "<<val1<<endl;
//If the above argument succeeds, largest and smallest will get their values
largest=val1;
smallest=val2;}
int their_sum=val1+val2;
int their_product=val1*val2;
int their_diff=val1-val2;
double ratio1;
ratio1=largest/smallest;
cout<<"Sum: "<<their_sum<<endl;
cout<<"Difference: "<<their_diff<<endl;
cout<<"Product: "<<their_product<<endl;
cout<<"Ratio: "<<ratio1;
}
return 0;
}
There is nothing new in this code, everything was covered in the previous chapters.
If at all you need ratio of two numbers say a,b in the form of n:m (where n>=1) then simply find the GCD(a,b) and divide a,b with this result.
eg:
a=4,b=6;
GCD(a,b)=2;
n=4/2=>2
m=6/2=>3
so ratio of 4 and 6 is 2:3
#include<iostream>
using namespace std;
class Test
{
public:
void check()
{
int x,y;
cout<<"Enter 1st number";
cin>>x;
cout<<"Enter 2nd number";
cin>>y;
int a;
int d= gcd(x,y);
cout<< x/d << " : " << y / d << endl;
}
int gcd(int x, int y) // 14, 21
{
int d;
if(y>x)
{
y=x+y;
x=y-x;
y=y-x;
}
for(int i=1; i<=y; i++)
{
if(x%i==0 && y%i==0 )
{
d=i;
}
}
return d;
}
};
int main()
{
Test t;
t.check();
return 0;
}
#include <iostream>
using namespace std;
int main()
{
int val1,val2;
cout << " Enter two integer values followed by enter" << endl << endl;
cin >> val1;
cin >> val2;
if(val1 < val2) // To determine which value is larger and which one is smaller
{
cout << val1 << " is smaller than" << val2 << endl << endl << "And" << val2 << " is larger than " << val1 << endl<<endl;
}
enter code here
else if( val2 < val1)
{
cout<<val2 <<" is smaller than"<< val1<<endl<<endl<<"And"<< val1 << " is larger than "<< val2<< endl << endl;
}
cout << "The sum of "<< val1<<" and "<<val2<<" is "<< val1+val2<<endl<<endl;
// diplaying the sum of the two numbers
enter code here
cout << " The difference between "<<val1<< " and "<<val2<< " is " << val1-val2<<endl;
// displays the difference of val2 from val1
cout << " The difference between "<<val2<< " and "<<val1<< " is " << val2-val1<<endl;
// displays thr difference of val1 fromval2
enter code here
enter code here
cout << " The product of " <<val1<< " and " << val2<< " is " << val1*val2<< endl<<endl;
// displaying the product of val1 and val2
enter code here
enter code here
enter code here
// now to diplay the ratio of the two numbers
double ratio1;
cout << " The ratio of "<<val1<<" and "<<val2<<" is ";
if(val1 < val2)
{
ratio1= ((double)val2) /val1;
cout << ratio1;
}
else if(val1 > val2)
{
ratio1= ((double)val1) /val2;
cout << ratio1;
}
}
could you please help me with solving simple problem? I am very fresh with C++ and learning from book "Programming: Principles and Practice Using C++ by Bjarne Stroustrup". I have never learnt C++ before so I am not familiar with many useful features. The drill says:
"6. Now change the body of the loop so that it reads just one double
each time around. Define two variables to keep track of which is the
smallest and which is the largest value you have seen so far. Each
time through the loop write out the value entered. If it’s the
smallest so far, write the smallest so far after the number. If it is
the largest so far, write the largest so far after the number"
I do not know how to do this correctly without using vector. Here is my code:
#include "C:/std_lib_facilities.h"
int main()
{
double a, b,differ=0;
char c=' ';
cout << "Enter two values: \n";
while (c != '|' && cin >> a >> b )
{
if (a > b)
{
cout << "The smaller value is: "<< b << " and the larger value is: " << a << "\n \n";
differ = a - b;
if (differ < 1.0 / 100)
cout << "Numbers are almost equal\n\n";
}
else if (a < b)
{
cout << "The smaller value is: " << a << " and the larger value is: " << b << "\n \n";
differ = b - a;
if (differ < 1.0 / 100)
cout << "Numbers are almost equal\n\n";
}
else
{
cout << "These values are equal!\n";
}
cout << "Enter a character | to break loop: \n";
cin >> c;
}
cout << "You have exited the loop.\n";
keep_window_open();
}
And here are previous steps, these I have solved with code above:
Write a program that consists of a while-loop that (each time around the loop) reads in two ints and then prints them. Exit the
program when a terminating '|' is entered.
Change the program to write out the smaller value is: followed by the smaller of the numbers and the larger value is: followed by the
larger value.
Augment the program so that it writes the line the numbers are equal (only) if they are equal.
Change the program so that it uses doubles instead of ints.
Change the program so that it writes out the numbers are almost equal after writing out which is the larger and the smaller if the two
numbers differ by less than 1.0/100.
Could you give me some hint how to do step 6.? I had some ideas but none of them worked..
Here is new code:
#include "C:/std_lib_facilities.h"
int main()
{
double smallestSoFar = std::numeric_limits<double>::max();
double largestSoFar = std::numeric_limits<double>::min();
double a,differ=0;
char c=' ';
cout << "Enter value: \n";
while (c != '|' && cin >> a)
{
if (a > largestSoFar)
{
largestSoFar = a;
cout <<"Largest so far is: "<< largestSoFar << endl;
}
else if (a < smallestSoFar)
{
smallestSoFar = a;
cout <<"Smallest so far is: "<< smallestSoFar << endl;
}
else if(smallestSoFar >= a && a<=largestSoFar)
cout << a << endl;
cout << "Enter a character | to break loop: \n";
cin >> c;
}
cout << "You have exited the loop.\n";
keep_window_open();
}
I do not know how to do this correctly without using vector.
You do not need vector for this. The description correctly says that two variables would be sufficient:
// Declare these variables before the loop
double smallestSoFar = std::numeric_limits<double>::max();
double largestSoFar = std::numeric_limits<double>::min();
Modify your loop to read into a, not into both a and b. Check the newly entered value against smallestSoFar and largestSoFar, do the printing, and re-assign smallest and largest as necessary. Note that the first time around you should see both printouts - for largest so far and for smallest so far.
Based on the knowledge that you are suppose to know at the current stage for the this assignment. The code should go something like this:
#include < iostream>
#include < cstdlib>
int main() {
double num_1 = 0;
double num_2 = 0;
double largest = 0;
double smallest = 0;
bool condition1 = true;
while (true) {
std::cin >> num_1;
if (num_1 > largest){
largest = num_1;
}
else if (num_1 < smallest) {
smallest = num_1;
}
std::cout << "The largest so far: " << largest << std::endl;
std::cin >> num_2;
if (condition1) {
smallest = largest;
condition1 = false;
}
if (num_2 < smallest) {
smallest = num_2;
}
else if (num_2 > largest) {
largest = num_2;
}
std::cout << "The smallest so far: " << smallest << std::endl;
}
system("pause");
return 0;
}
double large = 0;
double small = 0;
double input;
int counter = 0;
while (counter < 5) {
cin >> input;
cout <<"Large value: "<< large << '\t' <<"Small value: "<< small\
<< '\t' <<"Input value: "<< input << '\n';
if (input < small) {
cout << "The smallest value is " << input<<\
"\nthe largest value is "<< large<<'\n';
small = input;
}
else if (input > small&& input < large) {
cout << "The smallest value is " << small << \
"\nthe largest value is " << large<<'\n';
}
else if (input > small&& input > large) {
cout << "The smallest value is " << small << \
"\nthe largest value is " << input << '\n';
large = input;
}
counter += 1;
I went thru so many version of the algorithm to sort smallest and largest that my brain is fried. The book up to this point and searching online haven't helped at all.
I'm having difficulties at saving the last.
I used 3 in, 10 cm and 5 cm as test cases. Entering 3 in first, becomes the largest, entering 5 cm second becomes smallest and then 10 cm becomes smallest again. Tried different version for over 2 hours, even re-wrote that entire section. In the book Programming Principles and Practices using C++, its in the review section, before that I cant find anything to help me out.
#include <iostream>
#include <vector>
#include <algorithm>
#include <string>
#include <stdlib.h>
#include <iomanip>
using namespace std;
int main()
{
vector<double>all_meters;
double smallest= 0,print_smallest, largest = 0,print_largest, num = 0;
string unit, s_input, num_s_input, small_unit, large_unit;
while(cin.good()){
cout << "\n\t\t\t\tEnter '|' to exit.\n\n";
cout << "\t\tNumber to compare followed by white space and unit:";
cin >> num_s_input;
if(num_s_input.compare("|") == 0 || (s_input.compare("|") == 0)){
double sum = 0;
for (double x : all_meters) sum+=x;
cout << "Sum: " << setprecision(4) << sum << "m\n";
cout << "Smallest number: " << print_smallest << small_unit << endl
<< "Largest number: " << print_largest << large_unit << endl
<< "Total number of values: " << all_meters.size() << endl
<< "All the entered numbers converted to meters are: \n";
for (double i = 0; i<all_meters.size(); ++i){
cout << all_meters[i] << setprecision(2) <<"m ";
}
cout << "\nAlright now, goodbye then !\n" << endl;
break;
}
else{
cin >> s_input;
num = strtod(num_s_input.c_str(), NULL);
unit = s_input;
double meter = 0;
if(unit=="cm"){
meter = num / 100;}
else if(unit=="in"){
meter = num / 39.370;}
else if(unit=="ft"){
meter = num / 3.2808;}
else if(unit=="m"){
meter = num;}
else {
cout << "\n\tYou entered wrong unit!\t\n";}
if(largest==0){
largest = meter;
print_largest = num;
large_unit = unit;
cout << num << unit << " largest so far.\n";
}
else if(smallest==0&&meter<largest){
smallest = meter;
print_smallest = num;
small_unit = unit;
cout << num << unit << " smallest so far.\n";
}
else if(largest<meter){
largest = meter;
print_largest = num;
large_unit = unit;
cout << num << unit << " largest so far.\n";
}
else if(smallest>meter){
smallest = meter;
print_smallest = num;
small_unit = unit;
cout << num << unit << " smallest so far.\n";
}
all_meters.push_back(meter);
sort(all_meters.begin(),all_meters.end());
}
}
}
Managed to solve it without using limit, added the new changes to the code. Thanks for the help guys !
More than likely your problem comes from the fact that you are initializing smallest to 0. If you never enter anything smaller than 0 then smallest will never change.
When finding the minimum and maximum values you want to set the the initial value to the largest or smallest number respectively that it can hold. So in this case we would use
double smallest = std::numeric_limits<double>::max();
double largest = std::numeric_limits<double>::lowest()
double num = 0;
This was anything in your data set should be less than smallest and everything should be grater than largest.
This does require #include <limits>
You need to choose a standard unit of measure. The question suggests meters, so use that (you can use float or double for this, depending on what precision you need).
The problem is then simple, create some variables for the sum, smallest seen, and largest seen, the for each new input, convert to the standard format, and update the variables.
The solution (to get you started, not working code) might look something like this:
// You can represent the different types of units as integers
float convertToMeters(float unconvertedValue, int unit) {
// Convert unconvertedValue based on unit
}
float smallest = std::numeric_limits<float>::max();
float largest = std::numeric_limits<float>::lowest();
float sum = 0.0f;
// Update for each new input
while (new_input) {
float convertedValue = convertToMeters(new_value, unit);
// Update total
sum += convertedValue;
// Update smallest and largest
if (convertedValue > largest) largest = convertedValue;
else if (convertedValue < smallest) smallest = convertedValue;
}
As Nathan mentioned, #include <limits> for the limits.
I have to create a program to calculate charges for airfare. It's a simple program so far and I am not done adding to it, but every time I run it the result turns out to be 0. Is there something missing in my code? I am a beginner and I would appreciate any advice on improving my code. Thank you.
#include <iostream>
using namespace std;
void main () {
int distance = 0;
int num_bags= 0;
int num_meals= 0;
double distance_price = distance * 0.15;
double bag_price = num_bags * 25.00;
double meal_price = num_meals * 10.00;
double total_airfare = 0.00;
cout << "CorsairAir Fare Calculator" << endl;
cout << "Enter the distance being travelled: " << endl;
cin >> distance;
cout << "Enter number of bags checked: " <<endl;
cin >> num_bags;
cout << "Enter the number of meals ordered: " << endl;
cin >> num_meals;
total_airfare = (distance_price + bag_price + meal_price);
cout << total_airfare;
}
Your confusion is completely understandable - the piece you're missing is that when you assign a variable, you're assigning the left side to the result of the right side at that moment in time. It's not like algebra, where you say f(x) = x + 5 and f(x) is always whatever x + 5 is.
So, you assign double distance_price = distance * 0.15 when distance is 0 (which you just initialized). distance_price remains 0 even after you ask for input and change distance.
Do your price calculations after you ask for input, and everything will work just fine.
You are calculating the distance_price bag_price meal_price with default values i.e. 0 not with the value which you took from user.
Below code works fine and you won't see the issue.
#include <iostream>
using namespace std;
// My compiler did not allow void main so used int main
int main () {
int distance = 0;
int num_bags= 0;
int num_meals= 0;
double distance_price ;
double bag_price ;
double meal_price;
double total_airfare;
cout << "CorsairAir Fare Calculator" << endl;
cout << "Enter the distance being travelled: " << endl;
cin >> distance;
cout << "Enter number of bags checked: " <<endl;
cin >> num_bags;
cout << "Enter the number of meals ordered: " << endl;
cin >> num_meals;
distance_price = distance * 0.15;
bag_price = num_bags * 25.00;
meal_price = num_meals * 10.00;
total_airfare = 0.00;
total_airfare = distance_price + bag_price + meal_price;
cout << total_airfare;
return 0;
}
Result
CorsairAir Fare Calculator
Enter the distance being travelled:
200
Enter number of bags checked:
2
Enter the number of meals ordered:
2
100
I am currently writing a program that estimates Pi values using three different formulas pictured here: http://i.imgur.com/LkSdzXm.png .
This is my program so far:
{
double leibniz = 0.0; // pi value calculated from Leibniz
double counter = 0.0; // starting value
double eulerall = 0.0; // value calculated from Euler (all integers)
double eulerodd = 0.0; // value calculated from Euler (odds)
double eulerallans; // pi value calculated from Euler series (all integers)
double euleroddans; // pi value calculated from Euler series (odd integers)
int terms;
bool negatives = false;
cin >> terms;
cout << fixed << setprecision(12); // set digits after decimal to 12
while(terms > counter){
leibniz = 4*(pow(-1, counter)) / (2*counter+1) + leibniz;
eulerall = (1/pow(counter+1,2)) + eulerall;
eulerodd = 32*(pow(-1, counter)) / (pow(2*counter + 1, 3)) + eulerodd;
counter++;
eulerallans = sqrt(eulerall*6);
euleroddans = pow(eulerodd, 1.0/3.0);
cin >> terms;
if (terms < 0){
if(!negatives)
negatives=true;
}
}
cout << right << setw(14) << "# TERMS" << setw(15) << "LEIBINZ" << setw(15) << "\
EULER-ALL" << setw(15) << "EULER-ODD" << endl;
cout << right << setw(14) << terms << " " << leibniz << " " << eulerallans << " "\
<< euleroddans <<endl;
cout << "There were " << negatives << " negative values read" << endl;
return 0;
}
The sample input file that I am using is:
1
6
-5
100
-1000000
0
And the sample output for this input file is:
1 4.000000000000 2.449489742783 3.174802103936
6 2.976046176046 2.991376494748 3.141291949057
100 3.131592903559 3.132076531809 3.141592586052
When I run my program all I get as an output is:
# TERMS LEIBINZ EULER-ALL EULER-ODD
1
4.000000000000
2.449489742783
1.000000000000
So, I have two problems with my program:
1) It is only reading the first value in the input file and stopping.
2) The equation for eulerodd seems to be off, but I can't figure out what the problem is.
EDIT: Thanks to #RaphaelMiedl, I solved problem 2. Now I only have problem 1 to deal with.
Help is greatly appreciated.
I don't have the time to go through all of your code but
euleroddans = pow(32*eulerodd, 1/3);
immediately jumped me when I skimmed over it. 1/3 is integer arithmetic and gives you 0. Probably not what you wanted, you probably want 1.0/3.0 or something of the like there.
Now a bit of a late addition since I had time to look at your code again. #paddy is right that you only got one input statement in your code.
I'd probably put the whole pi calculation and outputting in a function and then loop over the input like:
#include <iostream>
#include <cmath>
#include <iomanip>
using namespace std;
void my_pi_func(int term);
int main()
{
int term;
cout << fixed << setprecision(12); // set digits after decimal to 12
while (cin >> term){
my_pi_func(term);
}
return 0;
}
void my_pi_func(int term)
{
if (term <= 0){
cout << "\n\nNegative value or 0 read\n\n" << endl;
return;
}
double leibniz = 0.0; // pi value calculated from Leibniz
int counter = 0; // starting value
double eulerall = 0.0; // value calculated from Euler (all integers)
double eulerodd = 0.0; // value calculated from Euler (odds)
double eulerallans = 0.0; // pi value calculated from Euler series (all integers)
double euleroddans = 0.0; // pi value calculated from Euler series (odd integers)
while(term > counter){
leibniz = 4*(pow(-1, counter)) / (2*counter+1) + leibniz;
eulerall = (1/pow(counter+1,2)) + eulerall;
eulerodd = (pow(-1, counter)) / (pow(2*counter + 1, 3)) + eulerodd;
counter++;
eulerallans = sqrt(eulerall*6);
euleroddans = pow(32*eulerodd, 1.0/3.0);
}
cout << right << setw(14) << "# TERMS" << setw(15) << "LEIBINZ" << setw(15)
<< "EULER-ALL" << setw(15) << "EULER-ODD" << endl;
cout << right << setw(14) << term << " " << leibniz << " " << eulerallans
<< " " << euleroddans <<endl;
}
You can see a working version here. Note that I made some more slight adjustments. For one I changed terms into term since that plural s was somehow bothering me. Also I changed counter to be an int since a counter as double variable doesn't make sense in my opinion. Also I changed how negative/0 values output. But all in all you should get what you should change if you compare with yours.