这是一个混乱。没有重复@NoDakker的评论，下面是代码的缩写版本，显示了所需的操作。请注意，为了增加清晰度，一些变量已被重命名（并删除了注解）。

// heading stuff omitted for brevity
int main(void)
{
    double funds;
    int childTickets;
    int adultTickets;

    /* Get funds */ // omitted for brevity

    /* Get # of Child tickets */

    /* Get # of Adult tickets */

    int totTckts = PurchaseTickets( &funds, adultTickets, childTickets );

    // Notice that the function performs its task.
    // Reporting those results belongs in the calling function
    if( totTckts )
        printf( "%d tickets, and you have %.2f remaining.", totTckts, funds );
    else
        printf( "Insufficient funds to purchase those tickets." );

    return 0;
}

int PurchaseTickets( double *pFunds, int nAdult, int nChild )
{
    double Cost
        = (nAdult * ADULT_TICKET_PRICE)
        + (nChild * CHILD_TICKET_PRICE);

    if( *pFunds < Cost ) // Insufficient available funds?
        return 0; // no show

    *pFunds -= Cost; // subtract cost from "double funds;" variable in main()

    return nAdult + nChild; // return # of purchased tickets
}

在PurchaseTickets函数中有几个问题。

double remainingCash = *pRemainingCash;
pRemainingCash = &remainingCash;

这段代码复制pRemainingCash指向的值，然后将其指向本地副本。这段代码是正确的，但它似乎不是正确的做法。

pRemainingCash = remainingCash - totalCost;

这是你遇到一个错误，由于语法。它试图将浮点值分配给指针，而不是指针指向的内容。需要*pRemainingCash = remainingCash - totalCost;
这将解决错误，但不是问题，因为它修改的是本地副本，而不是传入的值。
另一个问题是，你应该检查他们是否能负担得起的门票之前减去成本。我希望，如果成本超过可用资金，你会离开可用资金不变。
以下是一个清理版本：

int PurchaseTickets(double *pRemainingCash, int adultTickets, int childTickets)
{
    double adultCost = (adultTickets * ADULT_TICKET_PRICE);
    double childCost = (childTickets * CHILD_TICKET_PRICE);

    double totalCost = adultCost + childCost;
    int totalTickets = adultTickets + childTickets;

    if (*pRemainingCash >= totalCost)
    {
        // Subtract cost here
        *pRemainingCash -= totalCost;
        // Note *pRemainingCash in the next line. 
        // You need to dereference to obtain the value pointed at.
        printf("You have purchased %d tickets, and you have %.2f remaining.",
            totalTickets, *pRemainingCash);

        // Return success
        return totalTickets;
    }
    // This code won't be reached in the success case because of the return.
    // Removing the else avoids the possibility of the compiler warning that
    // all paths do not return a value.
    printf("You do not have enough money to purchase the tickets.");
    return 0;
}

main中的另一个小建议。
而不是double *pfunds = &funds;只是调用像PurchaseTickets(&funds, adultTickets, childTickets);这样的函数
你所拥有的工作，但我认为最好不要创建一个额外的变量。如果在此之后还有更多的代码，则可能会混淆使用哪一个。

我检查了你的代码，从我所看到的理想的解决方案来看，这个程序的上下文真的不需要指针。首先，由于“PurchaseTickets”函数实际上并不返回任何所需的信息，因此将其设置为空返回条目更有意义。其次，由于函数所需的输入变量可以全部作为值传递，因此真的不需要发送指针引用。
为了最小化对代码的影响，可以在函数中将以下语句与“printf”语句的重构一起沿着注解掉。

//double remainingCash = *pRemainingCash;           // Not needed
    //pRemainingCash = &remainingCash;

    //pRemainingCash = remainingCash - totalCost;

    if (*pRemainingCash >= totalCost)
    {
        printf("You have purchased %d tickets, and you have %.2f remaining.",totalTickets, *pRemainingCash - totalCost);    // Note remainder calculation
    }

这在终端产生了以下测试输出。

craig@Vera:~/C_Programs/Console/TicketPurchase/bin/Release$ ./TicketPurchase 
How much money do you have to purchase tickets?
800
How many child tickets would you like to purchase?
4
How many adult tickets would you like to purchase?
4
You have purchased 8 tickets, and you have 384.00 remaining.

注意代码的观察和简化的事情，下面是你的程序的重构版本。

#include <stdio.h>

#define ADULT_TICKET_PRICE 69.00                                                    //define constants
#define CHILD_TICKET_PRICE 35.00

void PurchaseTickets(double pRemainingCash, int adultTickets, int childTickets);    //declare function PurchaseTickets()

int main(void)
{
    double funds;
    int childTickets;
    int adultTickets;

    printf("How much money do you have to purchase tickets? ");
    if(scanf("%lf", &funds) != 1)                       //check for errors in user input
    {
        printf("Invalid input, exiting program.\n");
        return 1;                                       //will exit program if invalid characters are entered
    }

    printf("How many child tickets would you like to purchase? ");
    if(scanf("%d", &childTickets) != 1)                 //check for errors in user input
    {
        printf("Invalid input, exiting program.\n");
        return 1;                                       //will exit program if invalid characters are entered
    }

    printf("How many adult tickets would you like to purchase? ");
    if(scanf("%d", &adultTickets) != 1)                 //check for errors in user input
    {
        printf("Invalid input, exiting program.\n");
        return 1;                                       //will exit program if invalid characters are entered
    }

    PurchaseTickets(funds, adultTickets, childTickets);

    return 0;
}

/*****************************************************************************************
 *
 *  Function:  PurchaseTickets()
 *
 *  Parameters:
 *
 *      pRemainingCash - points to a variable containing the amt of cash from user
 *      adultTickets - specifies the number of adult tickets the user wants to buy
 *      childTickets - specifies the number of child tickets the user wants to buy
 *
 *  Description:
 *
 *      The function will determind if the user has enough money to purchase the
 *      specified number of tickets. If they do, the function deducts the proper funds
 *      from their remaining cash and returns the total number of tickets purchased.
 *      if they do not the function returns 0.
 *
*****************************************************************************************/

void PurchaseTickets(double pRemainingCash, int adultTickets, int childTickets)
{
    double adultCost = (adultTickets * ADULT_TICKET_PRICE);
    double childCost = (childTickets * CHILD_TICKET_PRICE);
    double totalCost = adultCost + childCost;

    int totalTickets = adultTickets + childTickets;

    pRemainingCash -= totalCost;

    if (pRemainingCash >= 0.00)
    {
        printf("You have purchased %d tickets, and you have %.2f remaining.\n",totalTickets, pRemainingCash);
    }

    else
    {
        printf("You do not have enough money to purchase the tickets.\n");
    }

    return;
}

请注意以下改进：

• “PurchaseTickets”函数的返回值已更改为“void”，因为整数返回值似乎没有用处。
• 所有变量都作为值传递，而不是使用任何变量指针。
• 删除了不必要的变量，以简化计算和比较。

在这些改进之后，接下来是对程序和购票功能的一系列额外测试。

craig@Vera:~/C_Programs/Console/TicketPurchase/bin/Release$ ./TicketPurchase 
How much money do you have to purchase tickets? 300.00
How many child tickets would you like to purchase? 4
How many adult tickets would you like to purchase? 4
You do not have enough money to purchase the tickets.
craig@Vera:~/C_Programs/Console/TicketPurchase/bin/Release$ ./TicketPurchase 
How much money do you have to purchase tickets? 600
How many child tickets would you like to purchase? 4
How many adult tickets would you like to purchase? 4
You have purchased 8 tickets, and you have 184.00 remaining.

概括一下，在函数中传递变量地址代替变量值是有正当理由的，但是应该始终了解函数的上下文以确定是否有必要。寻找关于函数定义的额外教程，以了解指针何时是有益的，这可能是明智的。