What happens when you pass a negative number to `inc`?

Question

There's a routine in Pascal called inc. It is used to increment numbers. There is another routine called dec, which is used to decrement numbers.

With only one argument, inc will increment the argument by one. Similarly, dec will decrement by one. You can specify a second argument, which says how much to increment or decrement by. In all the examples I've been able to find, the second argument is always positive.

I'm reviewing some code, and it appears to me that inc may get called with a negative second argument. What would happen? Is that allowed?

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Note: I'm reviewing this code as part of my work. I have no ability to compile and run the code, so I can't just try it and see what happens.

Answer 1

Calling Inc with a negative number as the second param will do the same as adding a negative number to an integer - it will decrease the value. For instance, using the integer variable i:

i := 10;
Inc(i, -10);  // i = 0, equivalent to i := i + -10
Inc(i, -10);  // i = -10, equivalent to i := i + -10

Dec with a negative number will do the reverse (increase the value). Following the last Inc above with Dec(i, -10) will result in i = 0 again.