C++ return value without return statement

Question

When I ran this program:

#include <iostream>

int sqr(int&);

int main()
{
    int a=5;
    std::cout<<"Square of (5) is: "<< sqr(a) <<std::endl;
    std::cout<<"After pass, (a) is: "<< a <<std::endl;
    return 0;
}

int sqr(int &x)
{
    x= x*x;
}

I got the following output:

Square of (5) is: 2280716
After pass, (a) is: 25

What is 2280716? And, how can I get a value returned to sqr(a) while there is no return statement in the function int sqr(int &x)?

Thanks.

Answer 1

Strictly, this causes undefined behavior. In practice, since sqr has return type int, it will always return something, even if no return statement is present. That something can be any int value.

Add a return statement and turn on warnings in your compiler (g++ -Wall, for instance).

int sqr(int &x)
{
    return x = x*x;
}