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Objective-C is C, so all C control flow works. Plus a few OC-specific constructs.

C-style if/else, switch, while, for

if (x > 0) {
    NSLog(@"positive");
} else if (x < 0) {
    NSLog(@"negative");
} else {
    NSLog(@"zero");
}

for (int i = 0; i < 10; i++) {
    printf("%d ", i);
}

switch (status) {
    case 200: printf("ok\n"); break;
    case 404: printf("not found\n"); break;
    default: printf("other\n");
}

fast enumeration

OC's for (Type *item in collection) syntax — like Python's for-in:

NSArray *names = @[@"Ada", @"Bob", @"Carol"];
for (NSString *name in names) {
    printf("%s\n", [name UTF8String]);
}

NSDictionary *ages = @{@"Ada": @36, @"Bob": @25};
for (NSString *name in ages) {       %% iterates over keys
    NSNumber *age = ages[name];
    printf("%s: %d\n", [name UTF8String], [age intValue]);
}

Fast and clean. The compiler optimizes this to direct iteration without a method call per element.

BOOL — yes / no / true / false

Objective-C historically uses YES/NO. Modern OC also accepts true/false:

BOOL active = YES;
if (!active) {
    NSLog(@"inactive");
}

BOOL is signed char (8-bit). For C++ interop or modern OC, prefer bool (one byte), but BOOL is the convention in Cocoa APIs.

Comparison

• == compares POINTERS (object identity)
• [a isEqual:b] compares VALUES
• [a isEqualToString:b] for strings (slightly faster — skips type check)

NSString *a = @"hello";
NSString *b = [NSString stringWithFormat:@"%@", @"hello"];
a == b              %% may or may not be YES (depends on string interning)
[a isEqual:b]       %% YES (same content)
[a isEqualToString:b]   %% YES (best for strings)

Nil checks

nil is the null pointer in OC. Sending a message to nil returns nil/0/NO — DOESN'T crash:

NSString *s = nil;
int len = [s length];      %% returns 0, no crash

This is unique to Objective-C. Most languages crash on null deref; OC silently returns the zero value. Both helpful and tricky.

Use explicit nil-checks when you need to distinguish:

if (obj == nil) {
    NSLog(@"missing");
}

%% Or:
if (!obj) {
    NSLog(@"missing");
}