目标C中的十六进制到二进制

Question

I have a program that takes the user input of an IOS text field and converts it into binary, hex, dec etc. I have been unable to implement an algorithm that convert Hexadecimal directly to binary without recursion. Any suggestions how to do this? This is what I have tried but it really doesn't work

 NSString *theNumber = [display text];
 NSMutableString *str = @"";
        for(NSInteger numberCopy = theNumber; numberCopy > 0; numberCopy >>= 1)
        {

           display.text = glGetString;[((numberCopy & 1) ? @"1" : @"0") atIndex:0];

Answer 1

- (NSString*)hexToBinary:(NSString*)hexString {
    NSMutableString *retnString = [NSMutableString string];
    for(int i = 0; i < [hexString length]; i++) {
        char c = [[hexString lowercaseString] characterAtIndex:i];

        switch(c) {
            case '0': [retnString appendString:@"0000"]; break;
            case '1': [retnString appendString:@"0001"]; break;
            case '2': [retnString appendString:@"0010"]; break;
            case '3': [retnString appendString:@"0011"]; break;
            case '4': [retnString appendString:@"0100"]; break;
            case '5': [retnString appendString:@"0101"]; break;
            case '6': [retnString appendString:@"0110"]; break;
            case '7': [retnString appendString:@"0111"]; break;
            case '8': [retnString appendString:@"1000"]; break;
            case '9': [retnString appendString:@"1001"]; break;
            case 'a': [retnString appendString:@"1010"]; break;
            case 'b': [retnString appendString:@"1011"]; break;
            case 'c': [retnString appendString:@"1100"]; break;
            case 'd': [retnString appendString:@"1101"]; break;
            case 'e': [retnString appendString:@"1110"]; break;
            case 'f': [retnString appendString:@"1111"]; break;
            default : break;
        }
    }

    return retnString;
}

This method does no verifying to ensure the passed string is actually a pure hex string, so that's something you may want to consider.

---

Alternatively, there's this option:

- (NSString*)hexToBinary:(NSString*)hexString {
    NSMutableString *retnString = [hexString mutableCopy];

    [retnString replaceOccurencesOfString:@"0"
                               withString:@"0000"
                                  options:NSCaseInsensitiveSearch
                                    range:NSMakeRange(0,[retnString length])];
    // repeat all the way through, much like above example

    return retnString;
}

The first example is certainly cleaner, I think. I'm not certain which example would be faster.