Functions and a clear policy

15-minute session: read for 3 minutes, trace for 3, experiment for 7, and complete the check for 2. Spend longer whenever you need.

A function or subroutine names a reusable calculation. Our policy accepts nonnegative total and completed counts and returns zero when completed reaches or exceeds total. Otherwise it returns their difference. Trace (4,1), (4,4), (4,5), and (0,0). Keep printing separate from calculation. Write down why negative inputs are outside this exercise’s domain, then design an explicit rejection policy before accepting external input.

Square brackets send a message to a receiver: [plan completed]. @interface declares methods and @implementation defines them. These GNUstep exercises use explicit memory management, not Apple ARC.

#import <Foundation/Foundation.h>
#include <stdio.h>
#include <assert.h>
int remaining(int total, int done) { return done >= total ? 0 : total - done; }
int main(void) {
    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
    printf("%d\n", remaining(4,1));
    [pool drain];
    return 0;
}

Expected result: 3

Practice and evidence

Keep three notes: your prediction, the actual result, and why they match or differ. The completion check grades understanding; the practice task builds skill.

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