What is the meaning of '==' in C?

Question

What is the meaning of == and how does it differ from =?

How do I know which one to use?

Answer 1

Now that you know the difference between '==' and '=", let me put you some words of caution. Although '==' is used as a standard test of equality between comparable variables and '=' used as an internally type-casted assignment, the following programming error is quiet common.

In the below example and similar codes, '=' is know as "Always true" conditional operator.

#include
int main()
{
    int i = 10, j = 20;
    if ( i = j )
        printf("Equal\n");
    else
        printf("NOT Equal\n");
    return 0;
}

So, the word of caution is "Never use '=' in if statements, unless you have something evil in your mind."