Converting between bases (binary and hexadecimal)

This lesson covers converting between bases in Objective-C, with the aim of deepening your understanding of how numbers are represented inside a computer.

Hexadecimal is straightforward with NSLog(@"%x", value), but there is no format specifier for binary, so you implement it yourself by repeatedly dividing and taking the remainder.

In the sample code, toBinary() takes the remainder with n % 2 and builds each binary digit by inserting at the front of the string with insertString:atIndex:0. Note the idea of inserting at the front rather than appending.

A common early stumble is precisely that absence of a standard binary function. Most languages provide one, so having to write the algorithm yourself is a surprise.

Binary is used inside the computer and hexadecimal in things like colour codes — basic knowledge worth having.

📖 Reference code

NSString *toBinary(int n) {
    if (n == 0) return @"0";
    NSMutableString *result = [NSMutableString string];
    while (n > 0) {
        [result insertString:(n % 2 == 0 ? @"0" : @"1") atIndex:0];
        n /= 2;
    }
    return result;
}

int num = 42;
NSLog(@"%@", toBinary(num));
NSLog(@"%x", num);
NSLog(@"%ld", strtol("101010", NULL, 2));

✍️ Your code

Type your code, then press "Run"

🧪 This site can't compile or run Objective-C directly, so it checks on the spot whether what you typed matches the reference code (scoring happens entirely in your browser — nothing is sent anywhere).