我正在教自己C乐趣。我在网上找了一些练习课程，找到了一个你输入两个输入的程序：一个是想象产品的数量，第二个是假想客户给你的金额。然后，您返回美元账单的数量，并将您给予客户的更改。
这是我为解决这个问题而编写的完整代码：
#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;
}
它工作正常，直到我打印出客户的镍和便士的数量。不是给我一个有意义的数字，而是给我一串随机的数字。
例如，这是这些输入的输出：
输入确切的项目数量（18.37）：123.32
输入客户提供的金额：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
现在如果程序运行正常，应该说：
但是我得到了那些随机（？）值。这可能是我没有清除指针的问题吗？我从未使用过使用它们的语言，而且我还没有学到足够的东西来正确使用它们。
我尝试将所有现金变量（例如oneHundred）设置为NULL，但它给了我这个编译错误：
change.c:204:14: warning: incompatible pointer to integer conversion assigning
to 'int' from 'void *' [-Wint-conversion]
oneHundred = NULL;
^ ~~~~
任何帮助都会很棒！我刚刚开始学习这门语言，我希望这个问题能给我一些关于如何在将来写出更好的C的见解！谢谢!!
答案 0 :(得分：3)
您不需要将它们设置为NULL因为它们不是指针，而是将它们初始化为0
cash = oneHundred = fifty = twenty = ten = five = one = quarter = dime = nickel = penny = 0;
NULL用于初始化指向特殊值的指针，因此您可以对其进行测试，以检查指针是否指向某处或是否指向。