Question

#include <stack>
using namespace std;

int main() {
    stack<int> s;
    int i;
    for (i = 0; i <= 10; i++) {
        s.push(i);
    }
    for (i = 0; i <= 10; i++) {
        printf("%d", s.pop());
    }
}

Whats wrong with the code above?

Error:

In function int main(): aggregate value used where an integer was expected

Answer 1

stack::pop is a void function which just discards the top element on the stack, in order to get the value you want to use stack::top.

The reason this is so is for exception safety reasons (what happens if the object returned throws an exception in its copy constructor?).