Switch statement inside while or do/while loop in c [closed] - c

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I am new to C, trying to make a simple banking system for an assignment in my C programming class. I decided to use a switch statement inside a while loop. The program runs without error messages in Visual studio, but behaves very oddly. Here is the assignment:
"Make a simple banking system. Start with the program asking for a starting balance for the savings account. From there it needs to ask which account should be modified: Savings, Checking, Loans, and Credit.
Checking needs to be set 250 dollars. This is the money available in the checking account to pay bills.
Loans needs to be set at 9000 dollars. This is the money owed on a loan. This is a bill.
Credit needs to be set at 500 dollars. This is the credit card balance owed. This is a bill.
The program should (after asking which account to modify) allow the user to move money within that section.
Sample: You are in Checking, do you want to pay a loan payment, credit payment, move money to savings from checking or return to the main menu.
Checking is your central point. You can move money any place from checking but you cannot pay a bill directly from Savings."
#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
int main(void)
{
int savings;
int checking = 250;
int loans = 9000;
int credit = 500;
int moneyMover;
char choice = 'y';
int service;
int service2;
printf("Welcome to C-Bank!\n\n");
printf("What is the current balance for savings? ");
scanf("%d\n", &savings);
printf("Thank you. \n\n");
while (choice == 'y')
{
printf("Which account or bill would you like to manage? \nPress '1' for Savings, '2' for Checking, '3' for Loans, or '4' for credit. Else, press any other key to exit.");
scanf("%d\n\n", &service);
switch (service)
{
case 1:
printf("Welcome to your savings account. Your current balance is %d. \n", savings);
printf("Please choose from the following: \nWould you like to (1) make a deposit, (2) make a transfer to checking, or (3) return to the main menu.\n");
scanf("%d", &service2);
if (service2 == 1)
{
printf("Enter deposit amount: \n");
scanf("%d \n", &moneyMover);
savings = savings + moneyMover;
printf("Your new balance is: %d\n", savings);
}
break;
default:
break;
}
printf("Would you like to choose another service? If so, press y, else press any other key.\n");
scanf(" %c", &choice);
}
printf("Thank you for using C-Bank. Come back soon!");
system("PAUSE");
return 0;
}
The program runs without error messages but acts weird. When you enter the initial savings amount, nothing happens until you press 'y', at which point it
apparently jumps inside the while loop, skips the switch statement, and waits for the you to pick again. Or, if you enter another number, it will quickly display the rest of the printf statements and end the program. Other weird things happen, too many to name really.

Answer 1

One problem is e.g. this
scanf("%d\n\n", &service);
The trailing newlines makes scanf read and discard any trailing white-space (space, newline, tab, etc.). But the problem with that is that scanf needs to see a non white-space character before it knows the end of the spaces to read and discard.
Don't have any trailing white-space in a scanf format string, it will seldom work as intended.
On the other hand you do the correct thing when reading the character for choice, when you use a leading space to read and discard leading white-space (like the newline from the previous input).
Another problem is that you state that after the savings input, you give the input 'y'. But that's not what the next input operation is expecting, it's expecting an integer for the service.
If you don't give the input as an integer, then
scanf("%d", &service);
will fail, and return 0 (you should really check what scanf returns). It will also mean that the 'y' in the input will be left in the input buffer for your read of choice. This is why it seems to skip the switch.
The first thing you should do after fixing the trailing space and newline in the format string, is to give the correct input. Then you can start adding error checks to make sure the input is correct.
One common way to handle possible incorrect input is to read whole lines using fgets and then use the string-scan function sscanf to parse the line. That way the invalid input will not be in the input buffer messing things up.