Does this usage of if statements cause undefined behaviour?

Question

I would like to know the correct usage of conditionals such as if statements to avoid undefined behaviours. Let's start with an example:

uint8_t x = 0;
bool y = false;
bool z = false;

if ((x == 135) and !y and !z) {
    //do something
}
else if ((x == 135) and y) {
    x = 5;
    z = true;   
}
else if ((x == 5) and z) {
    x = 135;
    z = false;
}
else {
    //do something
}

Now, will I get undefined behaviour by not including all 3 variables into every condition? Will every unaccounted for condition go into the else statement? If so, what happens if I get rid of the else statement? I have the exact same if statement (in a more complex scenario) and I seem not to be getting into the right statements every time.

Please enlighten me if there is a rule for this?

Answer 1

will I get undefined behaviour by not including all 3 variables into every condition?

The behaviour of not including all variables into every condition is not undefined by itself.

Will every unaccounted for condition go into the else statement?

Statement-false (i.e. the statement after the keyword else) is executed if the condition is false.

what happens if I get rid of the else statement?

The execution continues from the statement after the if statement.