Question

I’ve been looking at the Codility tests, (http://codility.com/) as I was thinking of trying to obtain a certificate, but I’ve come up against some very strange syntax errors, it’s seems to use a slightly different version of Objective-C to iOS.

For example, the function to complete was declared as so:

int equi (NSMutableArray *A) { //.... }

as opposed to

-(int)equi:(NSMutableArray *)A { //... }

and when I declared the following for loop (A is an array of NSNumber):

12. for (int i = 0; i < [A count]; i++){
13.    total = total + [[A objectAtIndex:i] intValue];   
14. }

it gave me the following compile errors:

func.m:12: error: 'for' loop initial declarations are only allowed in C99 mode
func.m:12: note: use option -std=c99 or -std=gnu99 to compile your code
func.m:13: error: invalid operands to binary + (have 'double' and 'id')

If anyone could shed any light on this, pre haps the version of objective-c or compiler version is different?

Thanks

EDIT: @Kos from Codility has commented below, they have recently switched their Objective-C compiler to Clang, which should mean most of the questions I’d asked are now non-issues.

Answer 1

Please note this question was strictly in the context of Codility, which does not explicitly tell you which version of C it is compiling against.

As H2CO3 pointed out, the declaration is a C-function. I was thrown because the test was supposed to be in Objective-C, not C, and while yes, Objective-C is a superset of C, I was expecting Objective-C syntax.

Codility does not give you access to compiler flags, hence why the stack trace was not useful. The problem was the initial declaration of i being inside the for loop declaration (C90 style). It should have be rewritten as this to be explicit:

int i = 0;
int count = [A count];
for (i = 0; i < count; i++) {
    total = total + [((NSNumber *)[A objectAtIndex:i]) intValue];
}