How to prevent unwanted variable assignment inside condition?

Typing = instead of == make unwanted assignment inside a condition. For example, consider the scenario below (this example is in C).

CASE A:

int g=1;

if ( g == 3 )
{
    printf("g is 3");   
}
else
{
    printf("g is not 3"); 
}

//this return: "g is not 3"

CASE B: (typo: missing = inside condition)

int g=1;

if ( g = 3 )
{
    printf("g is 3");   
}
else
{
    printf("g is not 3");
}

//this return: "g is 3"

Both the cases are formally correct, so the code will work but not as we want; and may be hard to debug.

How to prevent this situation?