将字符串与 C 中的结构成员进行比较

Question

I am attempting to create a small ticket pricing system. The user inputs the people accompanying them to the theme park as a command line argument (senior/adult/child/student) including themselves (what they are according to that list) and I compare the command line arguments with the struct members named tier - this part will be completed later with pointers to check each one, but until then I'm just attempting to get this lesser version of the completed program to work and cannot seem to. It won't allow me to compare a struct member (string) with a command line argument. I'm finding rectifying this slightly confusing because the error message

strcmpare.c:17:29: error: use of undeclared identifier 'senior' if (strcmp(argv[a], senior.tier[a]) == 0)

isn't yielding any clues as to what I should do. Here's the code so far (I am using the cs50 course and sandbox, thus the cs50.h header file. Apologies in advance, I'm not sure what the equivalent is in C):

#include <cs50.h>
#include <stdio.h>
#include <string.h>

struct ages
{
    char tier[7];
    int price;
};

void structorganizer(struct ages senior, struct ages adult, struct ages child, struct ages student);

int main(int argc, string argv[])
{
    for (int a = 0; a <= (argc-1); a ++)
    {
        if (strcmp(argv[a], senior.tier[a]) == 0)
        {
            printf("no errors");
            return 0;
        }
        printf("scrutinise more");
        return 1;
    }
}

void structorganizer(struct ages senior, struct ages adult, struct ages child, struct ages student)
{
    strcpy(senior.tier, "Senior");
    senior.price = 10;

    strcpy(adult.tier, "Adult");
    adult.price = 30;

    strcpy(child.tier, "Child");
    child.price = 0;

    strcpy (student.tier, "Student");
    student.price = 20;
}

Answer 1

First of all I think you should change the declaration of the struct to this: (I guess it's a good convention to start the structs name with Upper case)

typedef struct{
    char tier[7];
    int price;
}Age;

and then in the main, you have to create a new instance, for example:

int main(int argc, string argv[])
{
    Age senior;//HERE
    for (int a = 0; a <= (argc-1); a ++)
    {
        if (strcmp(argv[a], senior.tier[a]) == 0)
        {
            printf("no errors");
            return 0;
        }
        printf("scrutinise more");
        return 1;
    }
}

If you do this also change the struct name in the structorganizer function, like this

void structorganizer(Age senior, Age adult, Age child, Age student)

Answer 2

I'm finding rectifying this slightly confusing because the error message isn't yielding any clues as to what I should do.

On the contrary, it actually tells you EXACTLY what to do. That's not always the case with error messages, but here it is. The variable senior is not declared, so you need to declare it.

So where should you do that. You seem to want to use structorganizer to initialize things. Usually, global variables are a thing you want to avoid and there are certainly better ways of solving this, but just to quickly get things working. Remove all arguments from the function and declare global variables before, and call structorganizer first thing in main like this:

struct ages
{
    char tier[8]; // Changed to 8 because you need one more than the string length
    int price;
};

// Evil global variables, just to make code work with as little
// changes as possible
struct ages senior, adult, ages, child, student;

void structorganizer(); // Init the evil globals

int main(int argc, string argv[])
{
    structorganizer();

    // Continue as before

That should be enough to just get the code working, but you clearly need to spend more time with the basics here. The code you're writing right now is too advanced for you. No shame in trying though:)

There are absolutely cases where it's good to use an initializer function, but I cannot really say that this is one of them. I would declare them in main like this:

int main(int argc, string argv[])
{
    struct ages senior   = { .tier = "Senior",   .price=10 };
    struct ages adult    = { .tier = "Adult",    .price=30 };
    struct ages child    = { .tier = "Child",    .price=0  };
    struct ages student  = { .tier = "Student",  .price=20 };