/* Coin-changing program */

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

const int C1 = 200, C2 = 100, C3 = 50, C4 = 20, 
  C5 = 10,  C6 = 5,   C7 = 2,  C8 = 1;

int n1, n2, n3, n4, n5, n6, n7, n8;

int ReadInput(int *amount) {
  int input = 0 ;
  do {
    printf("Enter the amount (in pence) to be returned to the user: ");
    while (scanf("%d", &input) !=1) { scanf("%*s") ;
      printf("That wasn't a number - please try again: ");
    }
  } while (input < 0 ) ;
  *amount = input ;   // Set the value of amount to equal input
  return EXIT_SUCCESS ;
}

int CalculateCoins(int amount) {
  n1 = 0; n2 = 0; n3 = 0; n4 = 0; n5 = 0; n6 = 0; n7 = 0; n8 = 0; 
  int pot = amount;  // Total value of coins so far selected.
  while (pot > 0) {
    if (pot >= C1) {
      pot -= C1;  ++n1;
    } else if (pot >= C2) {
      pot -= C2;  ++n2;
    } else if (pot >= C3) {
      pot -= C3;  ++n3;
    } else if (pot >= C4) {
      pot -= C4;  ++n4;
    } else if (pot >= C5) {
      pot -= C5;  ++n5;
    } else if (pot >= C6) {
      pot -= C6;  ++n6;
    } else if (pot >= C7) {
      pot -= C7;  ++n7;
    } else {
      /*  pot >= C8.  (Why do we know this?) */
      pot -= C8;  ++n8;
    }
    assert(n1*C1 + n2*C2 + n3*C3 + n4*C4 + n5*C5 + n6*C6 + n7*C7 + n8*C8 == (amount - pot) && pot <= amount);
  }
  return EXIT_SUCCESS;
}

int PrintResult(int amount) {
 printf("%dp may be returned using the following \n", amount);
 printf("combination of coins:\n");
  if (n1) printf("%4d %dp coins,\n", n1, C1);
  if (n2) printf("%4d %dp coins,\n", n2, C2);
  if (n3) printf("%4d %dp coins,\n", n3, C3);
  if (n4) printf("%4d %dp coins,\n", n4, C4);
  if (n5) printf("%4d %dp coins,\n", n5, C5);
  if (n6) printf("%4d %dp coins,\n", n6, C6);
  if (n7) printf("%4d %dp coins,\n", n7, C7);
  if (n8) printf("%4d %dp coins.\n", n8, C8);
  return EXIT_SUCCESS;
}

int main(void) {
  int amount =0;
  if ( ReadInput(&amount) != EXIT_SUCCESS) {
    printf("Failure in ReadInput\n");
    return EXIT_FAILURE;
  }
  if ( CalculateCoins(amount) != EXIT_SUCCESS) {
    printf("Failure in CalculateCoins\n");
    return EXIT_FAILURE;
  }
  if ( PrintResult(amount) != EXIT_SUCCESS) {
    printf("Failure in PrintResult\n");
    return EXIT_FAILURE;
  }
  return EXIT_SUCCESS;
}