#include <iostream>
using namespace std;
void main()
{
    int a, b;

    cin >> a >> b;

    cout << "The sum is: " << output << endl;
}

You didn't declare output:

#include <iostream>

int main()
{
     int a, b;

     std::cout << "Enter first number: ";
     std::cin >> a;

     std::cout << "Enter second number: ";
     std::cin >> b;

     int output = a + b;

     std::cout << "\nThe sum is: " << output << std::endl;

    return 0;

}



Edited by author 25.07.2014 23:23

Your program must read and print only the data that is required in the problem statement. For example, you musn't print "Enter first number: " or "The sum is: ".