Program Rental Warnet

/*Program untuk menghitung biaya tagihannya berdasarkan lama pemakaian*/
#include <stdio.h>
#include <conio.h>
int potongan();
int a,c,tagihan,p;
char b[200],ulang;
main()
{
     
      ulang='Y';
      while (ulang=='Y')
      {
            printf("======================================");
            printf("\nPROGRAM TAMPILAN RENTAL\nKOMPUTER");
            printf("\n=======================================");
            printf("\nNo Komputer\t\t: ");
            scanf("%d",&a);
            printf("Nama Pemakai\t\t: ");
            scanf("%s",&b);
            printf("Lama Pakai (jam)\t: ");
            scanf("%d",&c);
     
            p=potongan();
            tagihan=c*1000-p;
     
            printf("\n\n======================================");
            printf("\nPROGRAM TAMPILAN RENTAL\nKOMPUTER");
            printf("\n=======================================");
            printf("\nNo Komputer\t\t: %d",a);
            printf("\nNama Pemakai\t\t: %s",b);
            printf("\nLama Pakai (jam)\t: %d",c);
            printf("\nPotongan\t\t: %d",p);
            printf("\nTotal Tagihan\t\t: %d",tagihan);
            printf("\n======================================");
            printf("\nUlangi Lagi [ Y/T ] ? ");
            scanf("%s",&ulang);
            printf("\n\n");
      }
      printf("Terima kasih");
      getch();
}

int potongan()
{
     if(c>5)
        p=c*75;
     else
     {
         p=0;
     }
     return(p);
}