Help with source code!

I am trying to write a program in C that simulate the billing of a telephone company. It should calculate the length of the call and the cost of the call. I am haveing trouble with adding an array where the summary shows the start time and end time of each call per customer. ***For example, Call 1 started at 23:45 and ended at 0:15. The duration of call 1 is 30 minutes.*** Below is a copy of my code that I have currently. Can You Help?!?
Thanks

#include <stdio.h>
#define reg_rate 0.25
#define discount 0.10
#define tax_rate 0.08
#define pm_discount 0.40

double Total_Time(double);
double Call_Cost(double);
double cost[10];

double tax, total_cost, sub_total, sub_total1, sub_total2,
       grand_total, cust_total, total_time;

int    response, hrs, min, end_hrs, end_min, cust_count, call_count, time_total, cust_time, cust_call_count;

main()
{
printf("\n*******Eastern Atlantic Telephone company*******\n\n");
  cust_count = 0;
  call_count = 0;
  grand_total = 0;
  time_total = 0;
  cust_time = 0;
  cust_call_count = 0;

  printf("\nDo you have a customer to process?");
  printf("\nEnter 1 for yes or 0 for No: ");
  scanf("%d", &response);
   while (response == 1)
    {
     cust_time = 0;
     cust_total = 0;
     ++cust_count;
     cust_call_count = 0;

     printf("\nEnter the start time of the call: ");
     scanf("%d:%d", &hrs, &min);
      if ((hrs >= 24) || (hrs < 0) || (min >=60) || (min < 0 ))
       {
        hrs = 0;
        min = 0;
        printf("\nThe time entered is incorrect!");
        printf("\nEnter the start time of the call: ");
        scanf("%d:%d", &hrs, &min);
       }

   printf("Enter the end time of the call: ");
   scanf("%d:%d", &end_hrs, &end_min);
   if ((end_hrs >= 24) || (end_hrs < 0) || (end_min >=60) ||  (end_min < 0 ))
       {
        end_hrs = 0;
        end_min = 0;
        printf("\nThe time entered is incorrect!");
        printf("\nEnter the end time of the call: ");
        scanf("%d:%d", &end_hrs, &end_min);
       }

     ++cust_call_count;
     ++call_count;

     total_time = Total_Time(total_time);
     total_cost = Call_Cost(total_cost);
     cost[10] = total_cost;

     printf("\nThe duration for this call is %.2f minutes.", total_time);

     cust_total += total_cost;
     time_total += total_time;
     cust_time += total_time;

     printf("\nDo you have a another call to process?");
     printf("\nEnter 1 for yes or 0 for No: ");
     scanf("%d", &response);
      while (response == 1)
       {
        ++cust_call_count;
        ++call_count;

        printf("\nEnter the start time of the call: ");
        scanf("%d:%d", &hrs, &min);
         if ((hrs >= 24) || (hrs < 0) || (min >=60) || (min < 0 ))
          {
           hrs = 0;
           min = 0;
           printf("\nThe time entered is incorrect!");
           printf("\nEnter the start time of the call: ");
           scanf("%d:%d", &hrs, &min);
          }

        printf("Enter the end time of the call: ");
        scanf("%d:%d", &end_hrs, &end_min);
         if ((end_hrs >= 24) || (end_hrs < 0) || (end_min >=60) || (end_min < 0 ))
          {
           end_hrs = 0;
           end_min = 0;
           printf("\nThe time entered is incorrect!");
           printf("\nEnter the end time of the call: ");
           scanf("%d:%d", &end_hrs, &end_min);
          }

        total_time = Total_Time(total_time);
        total_cost = Call_Cost(total_cost);
        cost[10] = total_cost;
     printf("\nThe duration for this call is %.2f minutes.", total_time);


     time_total += total_time;
     cust_total += total_cost;
     cust_time += total_time;

     printf("\nDo you have a another call to process?");
     printf("\nEnter 1 for yes or 0 for No: ");
     scanf("%d", &response);
    }
  printf("\n******Customer Summary Report******");

  printf("\nThe total number of calls is %d.", cust_call_count);
  printf("\nThe total time for this customer is %d minutes.", cust_time);
  printf("\nThe total for theis customer is $%.2f", cust_total);

  grand_total += cust_total;

  printf("\nDo you have a customer to process?");
  printf("\nEnter 1 for yes or 0 for No: ");
  scanf("%d", &response);
 }
printf("\nThe Grand Total is $%5.2f.", grand_total);
printf("\nThe Total Number of calls is %d.", call_count);
printf("\nThe Total Time used by all customers is %d minutes.", time_total);
printf("\nThe Total Number fo customers is %d.", cust_count);
}

double Total_Time(double total_time)
{
 if ((end_min < min ) && (end_hrs > hrs))
  {total_time = ((end_min + 60) - min) + ((end_hrs - 1 - hrs) * 60);}
 else if ((end_min >= min) && (end_hrs >= hrs))
  {total_time = (end_min - min) + ((end_hrs - hrs) * 60);}
 else if ((end_min < min) && (end_hrs < hrs))
  {total_time = ((end_min + 60) - min) + (((end_hrs -1) - (hrs - 24)) * 60);}
 else if ((end_min > min) && (end_hrs < hrs))
  {total_time = (end_min - min) + ((end_hrs - (hrs -24)) * 60);}
 return total_time;
}

double Call_Cost(double total_cost)
{
 if ((hrs < 18) && (hrs>= 8) && (total_time >= 60))
  {
   sub_total = total_time * reg_rate;
   sub_total1 = sub_total - (sub_total * discount);
   tax = sub_total1 * tax_rate;
   total_cost = sub_total1 + tax;
  }
 else if ((hrs < 18) && (hrs >=8))
  {
   sub_total = total_time * reg_rate;
   tax = sub_total * tax_rate;
   total_cost = sub_total + tax;
  }
 else if ((hrs >= 18) && (total_time >=60))
  {
   sub_total = total_time * reg_rate;
   sub_total1 = sub_total - (sub_total * pm_discount);
   sub_total2 = sub_total1 - (sub_total1 * discount);
   tax = sub_total2 * tax_rate;
   total_cost = sub_total2 + tax;
  }
 else if ((hrs >= 18) || (hrs < 8))
  {
   sub_total = total_time * reg_rate;
   sub_total1 = sub_total - (sub_total * pm_discount);
   tax = sub_total1 * tax_rate;
   total_cost = sub_total1 + tax;
  }
 else if ((hrs < 8) && (total_time >= 60))
  {
   sub_total = total_time * reg_rate;
   sub_total1 = sub_total - (sub_total * pm_discount);
   sub_total2 = sub_total1 - (sub_total1 * discount);
   tax = sub_total2 * tax_rate;
   total_cost = sub_total2 + tax;
  }
 return total_cost;
}