[renegade334]

If you are testing for truth, 0 is "false", and anything other than zero is "true".

Код:

if (0) {
    /*
        this code does not run, since 0 is a "false" value
        ...
    */
}

if (-1) {
    /*
        this code *does* run, since -1 is a "true" value
        ...
    */
}

If you want to do a different test, you need to specify it. To take Pottus's example above, if you have a function that returns a value greater than or equal to 0 on success, and returns -1 on failure:

Код:

if (myFunction() > -1) {
    // this will run if the function is successful
}

It all depends on the context.