Just use the printf formatting:
#include <stdio.h>
int main()
{
char* str = "Hello World";
printf("12345678901234567890\n");
printf("%20s\n", str);
printf("%-20s\n", str);
printf("%20.20s\n", str);
printf("%-20.20s\n", str);
printf("%10s\n", str);
printf("%-10s\n", str);
printf("%10.10s\n", str);
printf("%-10.10s\n", str);
return 0;
}
Try it and you'll see what I mean.