Change whether file is executable

This is a cocoa app that adds a right click menu option to change whether a file is executable. It works by executing the system command chmod on each of the files. But I want to know if there is a better way to change the permission of a file, such as a cocoa function that can change the permission of a file.

What are some other ways that I can improve my code?

#import "AppDelegate.h"

@implementation AppDelegate

- (void)applicationDidFinishLaunching:(NSNotification *)aNotification
{
    // Insert code here to initialize your application
    [NSApp setServicesProvider:self];
    NSUpdateDynamicServices();
}
void runSystemCommand(NSString *cmd)
{
    NSTask *task = [[NSTask alloc] init];
    [task setLaunchPath:@"/bin/chmod"];
    if ([[NSFileManager defaultManager] isExecutableFileAtPath:cmd]) {
        //NSLog(@"is executable \n");
        [task setArguments:@[ @"-x", cmd]];
        [task launch];

    } else {
        //NSLog(@"is not executable \n");
        [task setArguments:@[ @"+x", cmd]];
        [task launch];

    }
}
- (void)handleServices:(NSPasteboard *)pboard
              userData:(NSString *)userData
                 error:(NSString **)error {
    if([[pboard types] containsObject:NSFilenamesPboardType]){
        NSArray* fileArray=[pboard propertyListForType:NSFilenamesPboardType];
        int i;
        int count;
        count = [fileArray count];
        for (i = 0; i < count; i++){
            //NSLog (@"%@", [fileArray objectAtIndex: i]);
            runSystemCommand([fileArray objectAtIndex: i]);
        }
    }
}

@end

Here is the repository for the complete project.