c - 使用 struct 和 switch 的意外循环

Question

尝试编写一个以选项菜单开始的汽车租赁程序。选择后，应该执行所选选项，但是程序陷入了菜单->用户输入->菜单->用户输入->重复的循环。

我认为它与主函数中的“while ( choice = true )”有关。不过，我尝试过的任何方法都无法将其更改为 false。我也无法执行任何 case 语句中的任何内容。

#include <stdio.h>
#include <string.h>

#define true 1
#define false 0

void handleSelection (CompanyT *company, int choice);

void printMenu()
{
    printf ("1 Add new car to the inventory.\n");
    printf ("2 Make a reservation.\n");
    printf ("3 Find a reservation using a renter name and print it to the screen.\n");
    printf ("4 Check out a car given a renter name.\n");
    printf ("5 Print all available cars.\n");
    printf ("6 Calclate and print the average number of days rented.\n");
    printf ("7 Exit program.\n");
}
void handleSelection ( CompanyT *company, int choice)
{
    double value;
    switch ( choice) {
            case 1 :
                    value = 0;
                    choice = value;
                    printf ("%s", choice);
                    break; //optional(?)
            case 2 :
                    printf ("2");
                    break;
            case 3 :
                    printf ("3");
                    break;
            case 4 :
                    printf ("4");
                    break;
            case 5 :
                    printf ("5");
                    break;
            case 6 :
                    printf ("6");
                    break;
            case 7 :
                    choice = 0;
                    printf ("7");
                    break;

    default : printf ("Invalid entry.");
    }
    printf ("\n");
}

int main ( void )
{
    CompanyT myCompany;
    int     choice;
    //add pre-defined list of cars to the list
    createInventory ( &myCompany );

    while ( choice = true ) {
            printMenu();
printf ("Choose option: ");
  scanf ("%d", &choice);  
    handleSelection;
    };
    printf ("\n");

    return 0;
}

完整的程序，如果你想编译它:

#include <stdio.h>
#include <string.h>

#define true 1
#define false 0

typedef short int BoolT; //random true/false value

typedef struct {  //struct that records a car's information
    int carId;
    char make[20];
    char model[20];
    int numDoors;
    double rate;
    //complete this
} CarT;

typedef struct {  //struct that identifies a possible renter
    char renterName[20];
    //complete this
} RentalT;

typedef struct {  //struct that makes a reservation for a predetermined renter
    char renterName[20];
    //complete this
} ReservT;

typedef struct {  //struct that tracks the number of cars and rentals
    CarT allCars[20];
    RentalT allRentals[20];
    //complete this
} CompanyT;

/**
 * Prints a menu to the screen.
 */
void printMenu();

/**
* Creates the intial inventory of cars the company owns.
* company - the company whose inventory will be initialized
*/
void createInventory ( CompanyT *company );

/**
 * Adds new car to the inventory.
 *
 * company  the company that will add a new res
 */
void addNewCar ( CompanyT *company );

/**
 * Creates a new reservation prompting the user for information
 *
* company - the company that will add a new reservation
*/
void makeReservation ( CompanyT *company );

/**
 * Finds a reservation prompting the user for a rental name to locate the res record.
 *
 * company - the company whose reservations will be searched
 */
int findReservation ( CompanyT *company );

void handleSelection (CompanyT *company, int choice);



void printMenu()
{
    printf ("1 Add new car to the inventory.\n");
    printf ("2 Make a reservation.\n");
    printf ("3 Find a reservation using a renter name and print it to the screen.\n");
    printf ("4 Check out a car given a renter name.\n");
    printf ("5 Print all available cars.\n");
    printf ("6 Calclate and print the average number of days rented.\n");
    printf ("7 Exit program.\n");
}

void handleSelection ( CompanyT *company, int choice)
{
    double value;

    switch ( choice ) {
            case 1 :
                    choice = 0;
                    printf ("%s", choice);
                    break; //optional(?)
            case 2 :
                    printf ("2");
                    break;
            case 3 :
                    printf ("3");
                    break;
            case 4 :
                    printf ("4");
                    break;
            case 5 :
                    printf ("5");
                    break;
            case 6 :
                    printf ("6");
                    break;
            case 7 :
                    choice = 0;
                    printf ("7");
                    break;

    default : printf ("Invalid entry.");

    }
    printf ("\n");
}

int main ( void )
{
    CompanyT myCompany;
    int     choice;

    //add pre-defined list of cars to the list
    createInventory ( &myCompany );

    while ( choice  = true ) {
            printMenu();
printf ("Choose option: ");
  scanf ("%d", &choice);  
    handleSelection;
    };


    printf ("\n");

    return 0;
}
void createInventory ( CompanyT *company )
{
    (*company).allCars[0].carId = 1234;
    strcpy ((*company).allCars[0].make, "Vw");
    strcpy ((*company).allCars[0].model, "Golf");
    (*company).allCars[0].numDoors = 2;
    (*company).allCars[0].rate = 66.0f;

    //complete this
}

void addNewCar ( CompanyT *company )
{
    //complete this
}

Answer 1

问题出在 while ( choice = true ) 语句中。

choice = true 是一个使 choice 为 true 的赋值。结果将是赋值的结果，所以你得到while(true)，这是一个无限循环。

在这种情况下，您真正​​需要的是 do while 循环，因为它将至少运行一次，然后检查 choice 的值

do {
    printMenu();
    printf ("Choose option: ");
   scanf ("%d", &choice);  
   handleSelection;
} while ( choice == true );