Objective-C Program to Convert Decimal to Binary (Loop, Recursion, Bitwise, NSString)

Overview

In this article, we will write Objective-C programs to convert a decimal number into binary using different approaches like loops, recursion, bitwise shifts, and NSString manipulations.

Objective-C is a C-based language, so these examples combine C logic with Objective-C syntax.

When Do You Need This?

• To build iOS/macOS tools that deal with binary logic

• To understand how low-level operations work in Objective-C

• To practice for systems-level or embedded programming interviews

Loop-Based Binary Conversion

// Convert decimal to binary using a while loop
#import <Foundation/Foundation.h>

NSString* binaryUsingLoop(int number) {
    if (number == 0) return @"0";
    NSMutableString *binary = [NSMutableString string];
    while (number > 0) {
        [binary insertString:[NSString stringWithFormat:@"%d", number % 2] atIndex:0];
        number = number / 2;
    }
    return binary;
}

int main() {
    @autoreleasepool {
        NSLog(@"Binary of 25: %@", binaryUsingLoop(25));
    }
    return 0;
}

Explanation

• % 2 gives the remainder (bit).

• Insert each bit at the beginning of the string.

• Simple while loop tracks until number becomes 0.

Output

Recursive Method for Binary Conversion

// Recursive approach to convert decimal to binary
NSString* binaryRecursive(int number) {
    if (number == 0) return @"";
    return [NSString stringWithFormat:@"%@%d", binaryRecursive(number / 2), number % 2];
}

int main() {
    @autoreleasepool {
        NSString *binary = binaryRecursive(18);
        NSLog(@"Binary of 18: %@", binary.length == 0 ? @"0" : binary);
    }
    return 0;
}

Explanation

• Recursive division by 2.

• Append remainder at each return step.

• Fallback for 0 handled using length check.

Output

Bitwise Shift Method

// Bitwise conversion from decimal to binary
NSString* binaryUsingBitwise(int number) {
    NSMutableString *binary = [NSMutableString string];
    BOOL started = NO;

    for (int i = 31; i >= 0; i--) {
        int bit = (number >> i) & 1;
        if (bit == 1) started = YES;
        if (started) [binary appendFormat:@"%d", bit];
    }

    return binary.length == 0 ? @"0" : binary;
}

int main() {
    @autoreleasepool {
        NSLog(@"Binary of 42: %@", binaryUsingBitwise(42));
    }
    return 0;
}

Explanation

• Shift the number to the right >> i and check each bit.

• Use & 1 to get the bit value.

• Start appending only after the first 1.

Output

NSString Built-in with Custom Formatter

// Using NSString and NSNumber for binary conversion
NSString* binaryUsingNSString(int number) {
    if (number == 0) return @"0";
    NSMutableString *binary = [NSMutableString string];
    while (number > 0) {
        [binary insertString:[@(number % 2) stringValue] atIndex:0];
        number /= 2;
    }
    return binary;
}

int main() {
    @autoreleasepool {
        NSLog(@"Binary of 13: %@", binaryUsingNSString(13));
    }
    return 0;
}

Explanation

• Similar to the loop method but uses NSNumber and NSString features.

• Great for Objective-C style string handling.

Output

Wrap-Up

In this Objective-C article, we explored 4 different ways to convert decimal to binary. Each method highlights different core concepts—loops, recursion, bitwise manipulation, and Objective-C string handling.