Full code for Objective-C 2.0 sample

full_code.m

#import <Foundation/Foundation.h>
#import <Foundation/NSAutoreleasePool.h>
#import <Foundation/NSException.h>
#import <Foundation/NSDebug.h>
#import <Foundation/NSObject.h>
#import <Foundation/NSString.h>
#import <Foundation/NSObjCRuntime.h>
#include <string.h>



#import <GNUstepBase/GSObjCRuntime.h>
#import <CW/CWTest.h>

NSNumber *ICKGetMaxProfit(NSArray *stockPricesYesterday, NSUInteger length);

void test_func(NSArray *tests) {
    for (NSArray *test in tests) {
        describe(@"Compare output results of function with ref values.", ^() {
            it(@"should match ref value", ^() {
                equal(ICKGetMaxProfit([test objectAtIndex:0], [[test objectAtIndex:0] count]),
                                    (NSNumber*)[test objectAtIndex:1]);
            });
        });
    }
}

void test(BOOL includePositive, BOOL includeNegative) {
    NSArray *positiveTests = @[
        @[@[@10, @20, @5], @10],
        @[@[@10, @5, @10, @20], @15],
        @[@[@10, @10, @10], @0]
    ];

    NSArray *negativeTests = @[
        @[@[@35, @20, @10], @(-10)],
        @[@[@30, @20, @10], @(-10)],
        @[@[@100, @70, @50], @(-20)]
    ];

    if (includePositive) {
        test_func(positiveTests);
    }

    if (includeNegative) {
        test_func(negativeTests);
    }
}

NSNumber *ICKGetMaxProfit(NSArray *stockPricesYesterday, NSUInteger length) {
    NSInteger minPrice, maxProfit;

    // make sure we have at least 2 prices
    NSString *errorDesc = [NSString stringWithFormat:@"parameter length: expected 2 or more but got %lu", (unsigned long)length];
    NSCAssert(length >= 2, errorDesc);

    // we'll greedily update minPrice and maxProfit, so we initialize
    // them to the first price and the first possible profit
    minPrice = [[stockPricesYesterday objectAtIndex:0] integerValue];
    maxProfit = [[stockPricesYesterday objectAtIndex:1] integerValue] - [[stockPricesYesterday objectAtIndex:0] integerValue];

    // start at the second (index 1) time
    // we can't sell at the first time, since we must buy first,
    // and we can't buy and sell at the same time!
    // if we started at index 0, we'd try to buy *and* sell at time 0.
    // this would give a profit of 0, which is a problem if our
    // maxProfit is supposed to be *negative*--we'd return 0!
    for (NSUInteger i = 1; i < length; i++) {
        NSInteger currentPrice = [[stockPricesYesterday objectAtIndex:i] integerValue];

        // see what our profit would be if we bought at the
        // min price and sold at the current price
        NSInteger potentialProfit = currentPrice - minPrice;

        // update maxProfit if we can do better
        maxProfit = MAX(maxProfit, potentialProfit);

        // update minPrice so it's always
        // the lowest price we've seen so far
        minPrice = MIN(minPrice, currentPrice);
    }

    return @(maxProfit);
}

int main (int argc, const char * argv[])
{
    @autoreleasepool {
    test(YES, YES);
// TODO: tests for exceptions
    }
    return 0;
}