+ (NSString *)getBitStringForInt:(int)value {

    NSString *bits = @"";

    for(int i = 0; i < 8; i ++) {
        bits = [NSString stringWithFormat:@"%i%@", value & (1 << i) ? 1 : 0, bits];
    }

    return bits;
}

NSString *binaryRepresentation(int value)
{
    long nibbleCount = sizeof(value) * 2;
    NSMutableString *bitString = [NSMutableString stringWithCapacity:nibbleCount * 5];

    for (int index = 4 * nibbleCount - 1; index >= 0; index--)
    {
        [bitString appendFormat:@"%i", value & (1 << index) ? 1 : 0];
        if (index % 4 == 0)
        {
            [bitString appendString:@" "];
        }
    }

    return bitString;
}

NSString *str =  [ [NSString alloc] initWithBytes:barr length:sizeof(barr) encoding:NSUTF8StringEncoding]];

@interface NSString (BinaryStringRepresentation)

+ (NSString *)binaryStringRepresentationOfInt:(long)value;
+ (NSString *)binaryStringRepresentationOfInt:(long)value numberOfDigits:(unsigned int)length chunkLength:(unsigned int)chunkLength;

@end

@implementation NSString (BinaryStringRepresentation)

+ (NSString *)binaryStringRepresentationOfInt:(long)value
{
    const unsigned int chunkLength = 4;
    unsigned int numberOfDigits = 8;
    return [self binaryStringRepresentationOfInt:value numberOfDigits:numberOfDigits chunkLength:4];
}

+ (NSString *)binaryStringRepresentationOfInt:(long)value numberOfDigits:(unsigned int)length chunkLength:(unsigned int)chunkLength
{
    NSMutableString *string = [NSMutableString new];

    for(int i = 0; i < length; i ++) {
        NSString *divider = i % chunkLength == chunkLength-1 ? @" " : @"";
        NSString *part = [NSString stringWithFormat:@"%@%i", divider, value & (1 << i) ? 1 : 0];
        [string insertString:part atIndex:0];
    }

    return string;
}

@end

NSLog(@"%@", [NSString binaryStringRepresentationOfInt:0]);
NSLog(@"%@", [NSString binaryStringRepresentationOfInt:1]);
NSLog(@"%@", [NSString binaryStringRepresentationOfInt:2]);
NSLog(@"%@", [NSString binaryStringRepresentationOfInt:3]);
NSLog(@"%@", [NSString binaryStringRepresentationOfInt:7]);
NSLog(@"%@", [NSString binaryStringRepresentationOfInt:16]);

0000 0000
0000 0001
0000 0010
0000 0011
0000 0111
0001 0000

-(NSString *)toBinary:(NSInteger)input
{
 if (input == 1 || input == 0) {
 return [NSString stringWithFormat:@"%.8d", input];
 }
 else
 {
 NSString * myString = [NSString stringWithFormat:@"%@%d", [self toBinary:input / 2], input %    2];
 NSRange stringRange = {[myString length] - 8,8};
 NSString *shortString = [myString substringWithRange:stringRange];
 return shortString;
 }
}