Dynamically create a NSString stringWithFormat: output

Question

trying to figure out how to add zeroes in front of a random generated number with dynamic length of the number. For example if the number is 10 characters long, I can print the number as stringWithFormat:@"%.10d",i

Since the numer can somtimes be shorter than maximum length, it needs zeroes to fill the maximum length of the number to fit the string.

- (void)method:(int)length{
int i = rand() % length;
NSLog (@"%@",[NSString stringWithFormat:@"%.'length'd",i]);
}

Solution

NSLog (@"%@",[NSString stringWithFormat:@"%010d",i]); 

The meaning of format string components:

• 1st 0 - means that the number must be padded to specific width with zeros
• 10 - required minimum width of output

For more information about format specifiers you can check this printf specification. I sometimes also use this shorter one - you can find your example there.

You can create your format string dynamically as well - you'll need to calculate maximum number length in advance (maxLength in example):

NSString* format = [NSString stringWithFormat:@"%%0%dd", maxLength];
NSString *s = [NSString stringWithFormat:format, 10];
NSLog(@"%@", s);