How to left pad an integer with 0's (zeros)?

Question

I want the program to return 4 digits even if the number is less than 4 digits long.
for example:
1 -> 0001 I tried:

printf("%4d",number);

but it only returns three spaces then the number one, it doesn't add the 0s before.

Answer 1

By default, white spaces are used for padding, you should add 0 to the format specifier to make the padding character 0s.

printf("%04d",number);

Answer 2

In addition to Yu Hao's answer, you can also specify the digit count dynamically:

printf("%0*d", digit_count, number);