#include <stdio.h>
#include <stdlib.h>

char* format_width(double x, unsigned prec) {
  int fmt_size = snprintf (NULL, 0, "%%.%ulf", prec);
  char* fmt_string = malloc(fmt_size + 1);
  snprintf(fmt_string, fmt_size + 1, "%%.%ulf", prec);
  
  int out_size = snprintf (NULL, 0, fmt_string, x);
  char* out_string = malloc(out_size + 1);
  snprintf(out_string, out_size + 1, fmt_string, x);
  
  free(fmt_string);
  return out_string;
}

int main() {   
    double number;
    unsigned prec;
   
    printf("Enter a number: ");  
    
    // reads and stores input
    scanf("%lf", &number);
    
    printf("Enter precision: ");  
    
    // reads and stores input
    scanf("%u", &prec);
    
    char* result = format_width(number, prec);
    // displays output
    printf("You entered: %s", result);
    
    free(result);
    
    return 0;
}