Question

我一直在编写ATM接口的代码，其中包含一个必须由用户估算才能访问选项的引脚。一旦完成，我有5个选项可供选择，如快速现金，取款，存款和支票余额。一切似乎运行良好唯一的事情是，当用户存款，取款或获得快速现金时，账户余额不会更新到正确的金额。有人可以帮我解决这个问题。我会在下面发布我的代码

#include <stdio.h>

int fastCash(int amount);
int deposit(int deposit);
int withdraw(int balence);
void checkBalence(int balence);

int main()
{
    int pin;
    int pins = 9999;
    int pinTries = 1;
    int reciept;
    int options;
    int options2;
    int balence = 300;
    int fastCashChoice;
    printf("Enter your pin:");// the pin is 9999
    scanf("%d", &pin);
    while (pinTries <= 3)
    {
        if (pin == pins)
        {
            printf("Would you like a reciept:");
            //1 is equal to yes and 2 is equal to no
            scanf("%d", &reciept);
            printf("Choose from the following:\n");
            printf("1. Fast cash\n2. Withdraw\n3. Deposit\n4. Check balence\n5. Get card back");
            scanf("%d", &options);
            while (options <= 5)
            {
                switch (options)
                {
                case 1:
                    fastCash(fastCashChoice);
                    balence = balence - fastCashChoice;
                    break;

                case 2:
                    withdraw(balence);
                    break;

                case 3:
                    deposit(balence);
                    break;

                case 4:
                    checkBalence(balence);
                    break;

                case 5:
                    options2 == 2;
                    break;

                }
                printf("Would you like anohter transaction: ");// 1 is equal to yes and 2 is equal to no
                scanf("%d", &options2);
                if (options2 == 1)
                {
                    printf("1. Fast cash\n2. Withdraw\n3. Deposit\n4. Check balence\n5. Get card back");
                    scanf("%d", &options);
                }

                else
                {
                    options = 5;
                    pinTries = 4;
                    printf("Thank you for useing this ATM, GoodBye\n");
                }
            }
        }

        else if (pin != pins)
        {
            printf("Invalid pin, try again:");
            scanf("%d", &pin);
            pinTries++;
        }

        if (pinTries == 3)
        {
            printf("Sorry, you cant continue, please contact your bank");
        }
    }
    return 0;
}


int fastCash(int amount)
{
    int choice;
    printf("1. $20.00\n2. 40.00\n3. 80.00\n4. 100.00\n5. Exit");
    scanf("%d", &choice);

    switch (choice)
    {
    case 1:
        amount = 20;

    case 2:
        amount = 40;

    case 3:
        amount = 80;

    case 4:
        amount = 100;

    case 5:
        break;
    }

    return amount;
}

int withdraw(int balence)
{
    int withdrawAmount;
    printf("Enter the amount you would like to withdraw: ");
    scanf("%d", &withdrawAmount);
    balence = -withdrawAmount;
    return balence;
}

int deposit(int balence)
{
    int depositAmount;
    printf("Enter an amount you would like to deposit: ");
    scanf("%d", &depositAmount);
    balence += depositAmount;
    return balence;
}

void checkBalence(int balence)
{
    printf("Your current balence is: %d\n", balence);
    return;
}

Answer 1

当您将int（或任何其他非指针变量）传递给函数时，您只传递它的副本。如果函数然后更改它（如deposit，例如，），它将只更改传递的副本，并且不会影响原始变量。相反，您需要将指针传递给原始值。 E.g：

int deposit(int* balance)
{
    int depositAmount;
    printf("Enter an amount you would like to deposit: ");
    scanf("%d", &depositAmount);
    *balance += depositAmount;
}

调用函数应该将指针传递给这个变量而不是变量本身：

case 3:
deposit(&balance);
/* Here-^ */
break;

Answer 2

在您的代码中，您似乎只是将存款传入该功能，但您不会将其引用回原始balence变量，因此余额保持在300。

例如，在函数中：

int deposit(int balence)
{
   int depositAmount;
   printf("Enter an amount you would like to deposit: ");
   scanf("%d", &depositAmount);
   balence += depositAmount;
   return balence;
}

您刚刚发送了balence，但就像Mureinik所说的那样，您只是传递了原始值而没有更改其值（它只更改了balence < em> deposit()内的。

相反，您可以通过引用传入它，或者您可以将balence作为全局变量移动到代码的顶部，以便所有函数都可以看到它：

//code here.....
void checkBalence();

int balence = 300;
//more code here...

另外，请务必删除balence函数中的deposit()调用，以避免本地和全局变量之间存在歧义。

int deposit()
{
   /*..original code here..*/
}

...现在，在deposit()函数中，您的balence变量现在指向全局balence。

以下是最终的更正代码：

#include <stdio.h>

int fastCash(int amount);
int deposit();
int withdraw();
void checkBalence();

int balence = 300;

int main()
{
int pin;
int pins = 9999;
int pinTries = 1;
int reciept;
int options;
int options2;

int fastCashChoice;
printf("Enter your pin:");// the pin is 9999
scanf("%d", &pin);
while(pinTries <= 3)
{
   if(pin == pins)
   {
       printf("Would you like a reciept:");
       //1 is equal to yes and 2 is equal to no
       scanf("%d", &reciept);
       printf("Choose from the following:\n");
       printf("1. Fast cash\n2. Withdraw\n3. Deposit\n4. Check balence\n5. Get card back");
       scanf("%d", &options);
       while(options <= 5)
       {
           switch(options)
           {
               case 1:
               fastCash(fastCashChoice);
               balence = balence - fastCashChoice;
               break;

               case 2:
               withdraw(balence);
               break;

               case 3:
               deposit(balence);
               break;

               case 4:
               checkBalence(balence);
               break;

               case 5:
               options2 = 2;
               break;

           }
           printf("Would you like anohter transaction: ");// 1 is equal to yes and 2 is equal to no
           scanf("%d", &options2);
           if(options2 == 1)
           {
               printf("1. Fast cash\n2. Withdraw\n3. Deposit\n4. Check balence\n5. Get card back");
               scanf("%d", &options);
           }

           else
           {
               options = 5;
               pinTries = 4;
               printf("Thank you for useing this ATM, GoodBye\n");
               break;
           }
       }
   }

   else if(pin != pins)
   {
       printf("Invalid pin, try again:");
       scanf("%d", &pin);
       pinTries++;
   }

   if(pinTries == 3)
   {
       printf("Sorry, you cant continue, please contact your bank");
   }
}
return 0;
}


int fastCash(int amount)
{
int choice;
printf("1. $20.00\n2. 40.00\n3. 80.00\n4. 100.00\n5. Exit");
scanf("%d", &choice);

   switch(choice)
   {
       case 1:
       amount = 20;


       case 2:
       amount = 40;


       case 3:
       amount = 80;


       case 4:
       amount = 100;


       case 5:
       break;
}


return amount;
}

int withdraw()
{
int withdrawAmount;
printf("Enter the amount you would like to withdraw: ");
scanf("%d", &withdrawAmount);
balence -= withdrawAmount;
return balence;
}

int deposit()
{
  int depositAmount;
  printf("Enter an amount you would like to deposit: ");
  scanf("%d", &depositAmount);
  balence += depositAmount;
  return balence;
}

void checkBalence(int balence)
{
printf("Your current balence is: %d\n", balence);
return;
}

现在，它应按预期运行，这里产生的最终余额为176美元：

Enter your pin:9999
Would you like a reciept:1
Choose from the following:
1. Fast cash
2. Withdraw
3. Deposit
4. Check balence
5. Get card back2
Enter the amount you would like to withdraw: 124
Would you like anohter transaction: 1
1. Fast cash
2. Withdraw
3. Deposit
4. Check balence
5. Get card back4
Your current balence is: 176

Answer 3

嗯，解决问题的一个简单方法就是将int balence声明为全局。您可以在main()函数上方声明它，而不是在main()函数内声明它。

这将解决您当前的问题。

Answer 4

deposit和withdraw都返回更新的balance，但您不使用返回值。尝试将呼叫更改为：

case 2:
    balence = withdraw(balence);
    break;

case 3:
    balence = deposit(balence);
    break;

fastCash会返回要提取的现金金额，因此您需要更新main中的余额：

case 1:
    balence = balence - fastCash(fastCashChoice);
    break;

这避免了两个指针（你需要额外的错误处理，即检查NULL）和全局变量（这会使你的程序更复杂*）。

您的代码中还有一些问题。发送给fastCash的参数根本没有被使用，因为您返回要撤回的金额。

* Are global variables bad?

C中的ATM机

4 个答案: