NSInteger 转换为 NSString, 前面补上0,例如:1 -> 01
NSInteger num = 1;
NSString *str = [NSString stringWithFormat:@"%02ld", (long)num];
NSInteger 转换为 NSString, 前面补上0,例如:1 -> 01
NSInteger num = 1;
NSString *str = [NSString stringWithFormat:@"%02ld", (long)num];