Question

Example code:

#include <iostream>

int main()
{
    if(int a = std::cin.get() && a == 'a')
    {
        std::cout << "True" << std::endl;
    }
}

Question:

When I compile this code, visual studio gives me a nice warning: warning C4700: uninitialized local variable 'a' used. So I understand that a is uninitialized. However, I wanted to fully understand how the expression is evaluated. Is it the case that the if statement above is equivalent to if(int a && a == 'a') { a = std::cin.get(); }? Could someone explain exactly what happens?

Answer 1

The and operator && has higher precedence than the assignment operator =. So in other words, your statement is being executed like this:

if (int a = (std::cin.get() && a == 'a'))

You really want to use explicit parentheses:

int a;
if ((a = std::cin.get()) && a == 'a')

Even better, write clear code:

int a = std::cin.get();
if (a == 'a')

🙂