iOS: String Format for Numbers With Leading Zeros

To obtain a formatted String with a fixed number or digits, and any shortfall padding by leading zeroes,   use the following function call

[NSString stringWithFormat:@"%04d", i];

This will return a String containing the integer "i" and will always be 4 digit long. If i is 1, then the String will be "0001". If it is 12, then the String will be "0012".