Turbo C passing value in function - function

Question

i have this work that seems to be like an atm but my problem is i want to update balance but i cant. Say for instance when i first check the balance it gives out "0", then if i deposit "200" when i go to check for the balance again it gives me "200" now then after if i want to withdraw "100" then when i check for the balance it then should give me "100". but i have a problem in passing the values in functions. here is my work. please help me. oh by the way, im using DEV C+
#include <stdio.h>
#include <conio.h>
#include <stdlib.h>
// Declaring Functions that exist in the program.
int menu();
// End
// Main method at top, just to help with readability. And it can use the functions since we have already told main they exist.
int main()
{
int a = 0;
int option;
int atmDeposit();
int atmWithdrawal(int balance);
int atmCheck(int z);
system("cls");
do
{
option = menu();
switch(option)
{
case 1:
atmDeposit();
break;
case 2:
atmWithdraw(a);
break;
case 3: atmCheck(a);
break;
case 4:
printf("\nGoodbye!");
system("pause");
exit(0);
default:
printf("\nInvalid!\n");
break;
}
}
while (option != 4);
getch();
return 0;
}
int menu()
{
int op;
system("cls");
printf("What do you want to do?: \n");
printf("1 - Deposit\n");
printf("2 - Withdraw\n");
printf("3 - Check Balance\n");
printf("4 - Exit\n\n");
printf("Enter Choice: ");
scanf("%d",&op);
return op;
}
// End
// to check balance
int atmCheck(int z)
{
printf("\nYour Balance is P%d\n",z);
system("pause");
return z;
}
// End check balance
// to Deposit
int atmDeposit()
{
int deposit, a=0;
printf("\nHow much money do you want to deposit?: P");
scanf("%d", &deposit);
a += deposit;
printf("%d",a);
system("pause");
return a;
}
// end deposit
// to withdraw
int atmWithdraw(int balance)
{
int withdraw;
printf("\nHow much money do you want to withdraw?: P");
scanf("%d", &withdraw);
balance -= withdraw;
printf("%d",balance);
system("pause");
return balance;
}
// end withdraw

Answer 1

There are several things wrong here. First of all, the variables used in your withdrawal and deposit functions are limited in scope to those functions only. Hence, the next time you ask user to submit choice and perform action, the values assigned the last time are lost.
You can rectify this by using the variable a declared in main to store the balance, and then act on it in your other functions. However, if variable is declared in main, which is also a function, it will not be recognised in other functions. So, you need to declare it outside main, like so:
int menu();
int a = 0;
int main()
{
...
}
Next, in your atmDeposit function, you declare a local variable a. When you add the deposit amount to that, the value is retained only in that iteration. The next time you ask user to input a choice, the variable gets reset to 0 and your previous changes are lost. So, get rid of the local variable and use the global variable declared as above. The same fix is required for atmWithdraw and atmCheck functions - subtract the deposit from, and return, the global variable for balance amount.
Finally, I'm not sure why you need an input parameter for any of these functions, since you take input from user for deposit and withdrawal. So, remove the input parameters for functions. Additionally, I'm not sure why you want to return values, if you are only showing the new balance on screen in each case. So your function signatures should like:
void atmDeposit();
void atmWithdraw();
void atmCheck();

Answer 2

1) Declare your variable int a=0; globally (ie; outside the main function - as below). This allows all functions to access the common variable.
int a=0;
int main()
{
...
2) In function int atmDeposit(), remove the declaration a=0; .
3) In function int atmWithdraw(int balance) add the following line before system("pause");
a = balance;
With these changes the program works.