Deposit gives negative number? - c

Question

Good morning, guys! I'm currently a newly started programming learner. Down here is my code for a mini app store. However, there is a problem going on, yet I couldnt locate the problem.
The problem happen when I tried buying an app for $89.99 and I chose to redeem $10 9 times so I would have enough money to purchase the app (I didnt choose the $100 option because it would work just fine). However, the remained amount became $-79.99 instead of $0.01. Like I said, if I chose to deposit $100, the remained balance would be $10.01, which is normal. I don't get where I did wrong. Here is my code!
#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <ctype.h>
int Compare(double deposit, double choiceCost);
void DisplayApps(char *selectionPtr);
void SetCost(char selection, double *costPtr);
void PaymentOptions(double *depositPtr,double cost);
void DoItAgain(char *quitPtr);
//void Pay(double *depositPtr, double choiceCost);
void GetChange(double *depositPtr, double choiceCost);
void DoItAgain(char *quitPtr);
int main()
{
char selectionPtr;
char selection;
char quitPtr;
double costPtr;
double deposit = 0.0;
double choiceCost;
double depositPtr = 0.0;
double cost = 0.0;
printf("Welcome to the App Store\n");
printf("***************************\n\n");
printf("Your deposit is: %.2f\n", deposit);
printf("\n");
while (1)
{
do {
DisplayApps(&selectionPtr);
selection = selectionPtr;
SetCost(selection, &costPtr);
choiceCost = costPtr;
Compare(deposit, choiceCost);
while (Compare(deposit, choiceCost) == 0)
{
printf("Your balance isn't enough.\n");
printf("In order to purchase this item, you have to redeem more money.\n");
PaymentOptions(&depositPtr, cost);
deposit += depositPtr;
printf("You have redeemed $%.2f\n", depositPtr);
printf("Your balance now is: $%.2f\n", deposit);
printf("\n");
}
deposit = depositPtr;
GetChange(&depositPtr, choiceCost);
DoItAgain(&quitPtr);
} while (quitPtr == 'Y' || quitPtr == 'y');
return 1;
}
return 0;
}
void DisplayApps(char *selectionPtr)
{
printf("-------------------------\n");
printf("HERE ARE THE SLECTIONS\n");
printf("C -- Clown Punching $299.99\n");
printf("V -- Virtual Snow Globe $349.99\n");
printf("R -- Remote PC $999.99\n");
printf("G -- Grocery List Helper $2.99\n");
printf("M -- Mobile Cam Viewer $89.99\n");
printf("\n");
printf("Please enter a selection: ");
scanf(" %c", &*selectionPtr);
printf("\n");
}
void SetCost(char selection, double *costPtr)
{
if (selection == 'C' || selection == 'c')
{
*costPtr = 299.99;
}
else if (selection == 'V' || selection == 'v')
{
*costPtr = 349.99;
}
else if (selection == 'R' || selection == 'r')
{
*costPtr = 999.99;
}
else if (selection == 'G' || selection == 'g')
{
*costPtr = 2.99;
}
else if (selection == 'M' || selection == 'm')
{
*costPtr = 89.99;
}
}
int Compare(double deposit, double choiceCost)
{
if (deposit < choiceCost)
{
return 0;
}
else
{
return 1;
}
}
void PaymentOptions(double *depositPtr, double cost)
{
printf("You have (4) options to choose:\n");
printf("1 - $1000.00\n");
printf("2 - $500.00\n");
printf("3 - $100.00\n");
printf("4 - $10.00\n");
printf("How much do you want to redeem?");
printf(">>>>> ");
scanf("%lf", &cost);
printf("\n");
printf("-------------------------------------\n");
if (cost == 1)
{
*depositPtr = 1000.00;
}
else if (cost == 2)
{
*depositPtr = 500.00;
}
else if (cost == 3)
{
*depositPtr = 100.00;
}
else if (cost == 4)
{
*depositPtr = 10.00;
}
}
void GetChange(double *depositPtr, double choiceCost)
{
*depositPtr = *depositPtr - choiceCost;
printf("You have purchased this item successfully.\n");
printf("You still have $%.2f remained in you balance.\n", *depositPtr);
}
void DoItAgain(char *quitPtr)
{
printf("Do you want to continue purchase another item? [Y/N]\n");
scanf(" %c", &*quitPtr);
}

Answer 1

In this code : GetChange(&depositPtr, choiceCost);
You shold pass deposit (total deposit) and not &depositPtr (last deposit, only 10)