C pointer giving random value - c

Question

I am teaching myself C for fun. I looked online for some practice programs, and found one where you take two input's: One with the amount of an imaginary product, and second the amount of money the imaginary customers gives you. Then you return the number of dollars bills, and change you would give to the customer.
This is the complete code which I wrote to solve this problem:
#include <stdio.h>
#include <stdlib.h>
float getDif(float c, float m)
{
// First find the difference between
// c & m (m - c = d)
float dif = m - c;
// Return the difference
return dif;
}
void getChange(float dif, int* cash, float* change)
{
// If difference is less than 0 we have a problem
// because the customer gave us less money than
// the cost of the product
if(dif < 0)
{
fprintf(stderr, "The customer has not given enough money!...\n");
exit(EXIT_FAILURE);
}
// Cash is seen as the difference without any
// decimals. So if the difference is $13.45
// the cash would be 13 since cash is, in my
// mind paper money
*cash = (int) dif;
// Change is seen as the difference - cash
// if the difference is $13.45 the change
// would be .45
*change = dif - *cash;
}
void getCash(int cash, int* oneHundred, int* fifty, int* twenty, int* ten,
int* five, int* one)
{
if(cash == 0)
{
printf("Wow close to exact change! - No need for cash...\n");
// End the function there is no need to continue
return;
}
// Since cash is > 0 we need to determine the bills to return
// to the user
if(cash >= 100)
{
while(cash >= 100)
{
cash = cash - 100;
(void) ++*oneHundred;
}
}
if(cash >= 50)
{
while(cash >= 50)
{
cash = cash - 50;
(void) ++*fifty;
}
}
if(cash >= 20)
{
while(cash >= 20)
{
cash = cash - 20;
(void) ++*twenty;
}
}
if(cash >= 10)
{
while(cash >= 10)
{
cash = cash - 10;
(void) ++*ten;
}
}
if(cash >= 5)
{
while(cash >= 5)
{
cash = cash - 5;
(void) ++*five;
}
}
if(cash >= 1)
{
while(cash >= 1)
{
cash = cash - 1;
(void) ++*one;
}
}
printf("After all loops cash = %d\n", cash);
}
void getCoins(float change, int* quarter, int* dime, int* nickel, int* penny)
{
// To find the correct change we need to turn the
// current format of variable change (0.57) into
// a easier to work with 57.
int tenChange = change * 100;
if(tenChange >= 25)
{
while(tenChange >= 25)
{
tenChange = tenChange - 25;
(void) ++*quarter;
}
}
if(tenChange >= 10)
{
while(tenChange >= 10)
{
tenChange = tenChange - 10;
(void) ++*dime;
}
}
if(tenChange >= 5)
{
while(tenChange >= 5)
{
tenChange = tenChange - 5;
(void) ++*nickel;
}
}
if(tenChange >= 1)
{
while(tenChange >= 1)
{
tenChange = tenChange - 1;
(void) ++*penny;
}
}
printf("After all loops change = %d\n", tenChange);
}
int main(void)
{
// Create variables for the various things we create
float c, m, dif, change;
int cash, oneHundred, fifty, twenty, ten, five, one, quarter, dime, nickel,
penny;
printf("Enter the exact amount of the items (18.37): ");
// Obtain the cost
scanf("%f", &c);
printf("Enter the amount of money given by the customer: ");
// Obtain the money from customer
scanf("%f", &m);
// Obtain the difference of the cost
// And the money given by calling the
// getDif() function
dif = getDif(c,m);
// Send the difference to the getChange()
// function, as well as the pointers
// cash & change which will be used in the
// function and returned back here
getChange(dif, &cash, &change);
// First send the cash variable to the getCash
// function along with pointers for each bill
// The function will calculate the number of bills
// to give to the customer and return each
getCash(cash, &oneHundred, &fifty, &twenty, &ten, &five, &one);
// Print the number of bills to give to the customer
printf("Give the customer %d Hundred doller bill(s)!\n", oneHundred);
printf("Give the customer %d Fifty doller bill(s)!\n", fifty);
printf("Give the customer %d Twenty doller bill(s)!\n", twenty);
printf("Give the customer %d Ten doller bill(s)!\n", ten);
printf("Give the customer %d Five doller bill(s)!\n", five);
printf("Give the customer %d One doller bill(s)!\n", one);
// Second send the change variable to the getCoins
// function along with pointers for each type of
// coin. The function will calculate the number of
// coins to give to the customer and return each
getCoins(change, &quarter, &dime, &nickel, &penny);
// Print the number of coins to give to the customer
printf("Give the customer %d Quarter(s)\n", quarter);
printf("Give the customer %d Dime(s)\n", dime);
printf("Give the customer %d Nickel(s)\n", nickel);
printf("Give the customer %d Penny(s)\n", penny);
printf("%d\n", cash);
printf("%.2f\n", change);
printf("$%.2f\n", dif);
return 0;
}
It is working ok, until I print out the number of Nickels, and Pennies to the customer. Instead of giving me a number which would make sense it is giving me a random string of numbers.
For example this is the output for these inputs:
Enter the exact amount of the items (18.37): 123.32
Enter the amount of money given by the customer: 124.00
Wow close to exact change! - No need for cash...
Give the customer 0 Hundred doller bill(s)!
...
Give the customer 0 One doller bill(s)!
After all loops change = 0
Give the customer 2 Quarter(s)
Give the customer 1 Dime(s)
Give the customer 32768 Nickel(s)
Give the customer 1596836443 Penny(s)
0
0.68
$0.68
Now if the program was working correctly, it should say:
2 Quarter(s)
1 Dime(s)
1 Nickel(s)
3 Penny(s)
But I'm getting those random(?) values. Could this be a problem with me not clearing my pointers? I have never worked with a language that uses them, and I have not learned enough to use them properly.
I tried to set all the cash variables (for example oneHundred) to NULL, but it gives me this compiler error:
change.c:204:14: warning: incompatible pointer to integer conversion assigning
to 'int' from 'void *' [-Wint-conversion]
oneHundred = NULL;
^ ~~~~
Any help would be amazing! I am just beginning to learn this language, and I hope this question will give me some insight on how to write better C in the future! Thank you!!

Answer 1

You don't need to set them to NULL be cause they are not pointers, initialized them to 0 like this
cash = oneHundred = fifty = twenty = ten = five = one = quarter = dime = nickel = penny = 0;
NULL is used to initialized pointers to a special value, so you can test against it to check if the pointer is pointing somewhere or if it doesn't.