C ++未定义的引用？

Question

So this is a segment of my program, i am having trouble calling the the functions and I really need some help. It's basically to choose either function and enter data and later print that data. What am doing wrong ?please help, I keep getting

"[Linker] reference to Customer_Record()'" , [Linker error] undefined reference to Car_Record() ' and "ld returned 1 exit status"

 #include <stdio.h>
 #include <string.h>  
 #include <stdlib.h>
 #include <windows.h>  
 #include <conio.h>

void Customer_Record(), Car_Record();
int num;

struct Customer {
    char customer_ID[20];
    int license;
    char address[20];
    int phone;
    char email[20];
} cust;

struct car {

    int regno[20];
    char model[20];
    char colour[10];
} car;


main() {
    printf("               Enter 1 to go to Customer Record \n\n");
    printf("               Enter 2 to go to Car Record \n\n");
    scanf("%d", &num);
    if (num = 1) {
        Customer_Record();
    } else if (num = 2) {
        Car_Record();
    } else {
        printf("Invalid Number");
    }

    system("cls");

    void Customer_Record(); {
        printf("********CUSTOMER RECORD********"); /* accepts into*/
        printf("\nEnter the name of the customer ");
        scanf("%s", &cust.customer_ID);
        printf("Enter the license number of the customer ");
        scanf("%d", &cust.license);
        printf("Enter the address of the customer ");
        scanf("%s", &cust.address);
        printf("Enter the cell phone number of the customer ");
        scanf("%d", &cust.phone);
        printf("Enter the email address of the customer ");
        scanf("%s", &cust.email);
    }

    void Car_Record(); {
        printf("********CAR RECORD********");
        printf("\nEnter the car's registration number ");
        scanf("%d", &car.regno);
        printf("Enter the car's model ");
        scanf("%s", &car.model);
        printf("Enter the colour of the car ");
        scanf("%s", &car.colour);
    }
    getchar();
    getchar();
}

Answer 1

Don't nest your functions like that. The definitions of Customer_Record() and Car_Record() should be outside of main() . You need to take the ; off of the definitions of those functions, too.

Try formatting your code better - that will help a lot in the long run.

Answer 2

1. You're missing a } at the end of main, the compiler thinks your function declarations are within the main function.

2. Remove the trailing semicolon from your function. Ex:

    void Car_Record(); { 

   to

     void Car_Record() { 

That semicolon isn't necessary.

Answer 3

I've compiled a list of all the problems with your program. Here it is:

• Your if statements are using the assignment = operator when they should be using the comparison operator == . So for example, change the following:

   if (num = 1) { 

  to

   if (num == 1) { 

  This also occurs in your else statement as well.

• It is also incorrect to define functions inside of main. You must define these blocks outside the main clause. You've already prototyped the functions above main, now you must define them below main. In addition, you shouldn't have a semicolon after the parameter list when defining functions; that is syntactically wrong.

The following is advice. You're compiling this code as C++ but this is written using C functions/headers. In order to convert it to C++, do the following changes:

• Change your headers: stdio.h, conio.h, stdlib.h; these are all C-style headers. Essentially all headers that end in ".h" are C-style headers. C++ has its own I/O library, thus making its C equivalent obsolete. Include the following headers instead:

   #include <iostream> #include <cstdlib> 

  I left out additional headers because it seems you're only using printf / scanf and system , the equivalent of which C++'s iostream and cstdlib headers already possesses. For example, std::cout and std::cin for iosteam. And the equivalent of getchar is std::cin.get()`.

• Main returns int: In standard C++, you cannot elide the return type. Specify the return type of main as int , but you don't have to put return 0 at the end (this is implicit).

If you want to look up C++ functions and containers (like std::cout / std::cin ), this reference helps a lot.