C – The %x format specifier

Break-down:

• 8 says that you want to show 8 digits
• 0 that you want to prefix with 0‘s instead of just blank spaces
• x that you want to print in lower-case hexadecimal.

Quick example (thanks to Grijesh Chauhan):

#include <stdio.h>
int main() {
    int data = 29;
    printf("%x\n", data);    // just print data
    printf("%0x\n", data);   // just print data ('0' on its own has no effect)
    printf("%8x\n", data);   // print in 8 width and pad with blank spaces
    printf("%08x\n", data);  // print in 8 width and pad with 0's

    return 0;
}

Output:

1d
1d
      1d
0000001d

Also see http://www.cplusplus.com/reference/cstdio/printf/ for reference.