Program not taking expected Input, can't find out why-CodePudding

This program should take input a,b equal to the value of t, instead it seems to only take one input and then deliver the output. For example, the inputs of:

leads only to an output of:

the expected output should instead be:

1
100
10

The program:

#include <iostream>

using namespace std;

int main()
{
   int t;
   cin >> t;
   for(int i; i<t; i  ){
    int a, b;
    int x = a%b;
    cin >> a, b;
    cout << x;

   }
    return 0;
}

I have tried breaking up cin >> a, b; into two different commands but that didn't work. I also messed around with where the variables are located in the code. None of that helped.

CodePudding user response：

For starters using the initializer in the declaration

int x = a%b;

invokes undefined behavior because variables a and b were not initialized and have indeterminate values.

Also this statement

cin >> a, b;

is equivalent to the expression statement with the comma operator

( cin >> a ), b;

Instead you need to write

int a, b;

cin >> a >> b;

int x = a % b;

cout << x << '\n';

Also the variable i was not initialized in the for loop

for(int i; i<t; i  ){

You have to write

for ( int i = 0; i < t; i   ){

If you do not want to mix the input with the output when use the standard container std::vector<int> for example the following way

#include <iostream>
#include <vector>

int main()
{
    unsigned int t = 0;

    std::cin >> t;

    std::vector<int> v( t );

    for ( auto &x : v )
    {
        int a, b;

        std::cin >> a >> b;

        x = a % b;
    }

    for ( const auto &x : v )
    {
        std::cout << x << '\n';
    }

    return 0;
}

CodePudding user response：

common mistakes in using std::cout and std::cin ,is using comma instead of shift operator when seprate arguments passed to std::cin and std::cout.

so you should use ">>" of "," when pass new arguments:

std::cin >> a >> b;