Trailing Zeros in printf/sprintf

Question

I would like to make the output of a number to always have 6 digits

e.g.:

• if number is 1 the output should be 100000
• if number is 23 the output should be 230000
• if number is 236 the output should be 236000

How can I do this with printf/sprintf?

Answer 1

printf and its variants can pad zeroes to the left, not to the right. sprintf the number, then add the necessary zeros yourself, or make sure the number is 6 digits long:

while(num < 100000) 
    num *= 10;

(This code assumes the number isn't negative, or you're going to get in trouble)

Answer 2

printf will return the number of character printed out. This you can print out the remaining zeros:

int num = 3; // init
int len = printf("%d", num);
for (int i = 0; i < 6-len; ++i)
    printf("0");

You should add some error checks (for example, if len is larger than 6).

With sprintf, you can use memset on the remaining buffer, which will be easier.