Question

I encountered this problem in my program which was creating problems. so let me explain it by a example:

#include<iostream>

int func(){
        if(1==0) return 100;
}

int main(){

        int x=99;
        x= func();
        std::cout<<"Value of x: " << x <<std::endl;
}

I had thought the output will be 99 but output is 0, so what’s going on here?

Answer 1

You have undefined behavior because your function is declared to return an int but the execution path through the function never reaches a return statement.

In C++ it is illegal to exit a function defined as returning a non-void type other than via a return statement with an argument.

ISO/IEC 14882:2003 6.6.3 [stmt.return] / 2:

[…] Flowing off the end of a function is equivalent to a return with no value; this results in undefined behavior in a value-returning function.