case 3:

            while((tmp!=accountNum1)||(tmp!=accountNum2)){

               printf("Enter an account to withdraw (%d or %d?): ", accountNum1,accountNum2);
               scanf("%d", &tmp);


               if((tmp!=accountNum1)||(tmp!=accountNum2))
                  printf("invalid account number.\n");

            }
            printf("Enter an amount to withdraw: ");
            scanf("%d", &tmp);

         //input validation

            if (tmp== accountNum1){
               withdraw(accountNum1, &balance1, tmp);
            }
            else{
               withdraw(accountNum2, &balance2, tmp);
            }

            break;