C: Manipulating structs in separate functions

Question

I'm not sure if this is appropriate for this kind of forum, as it is a very specific question, but I'll ask anyway.

I have three files:

1. main.c
2. functions.c
3. functions.h

In functions.c and functions.h I have created a struct , and defined it as a type called control :

typedef struct
{
    char cUp, cLeft, cDown, cRight
} control;

I created an instance of control , and initialized the instance called Keys right at the beginning of main.c :

#include <stdio.h>
#include <stdlib.h>
#include "functions.h"

int main()
{
    control Keys = {'w', 'a', 's', 'd'};

    //...
}

I passed Keys into a function called options_f , which takes a control as its parameter and returns a control . The function prototype is placed in functions.h :

//in functions.h:
control options_f(control Keys);

//in main.c:
Keys = options_f(Keys);

options_f is located in functions.c and looks like this:

control options_f(control Keys)
{
    system("cls");

    printf("\nENTER | Place your symbol.\n\n1| %c |Move up.\n\n2| %c |Move left.\n\n3| %c  |Move down.\n\n4| %c |Move right.\n", Keys.cUp, Keys.cLeft, Keys.cDown, Keys.cRight);
    printf("\n\nTo change the keys: NUMBER,SYMBOL (enter 0 to return to menu).\n\n");

    int iTemp = 0;
    char cTemp = '\0';
    scanf("%i,%c", &iTemp, &cTemp);

    switch(iTemp)
    {
        case 0:
            break;
        case 1:
            Keys.cUp = cTemp;
            Keys = options_f(Keys);
            break;
        case 2:
            Keys.cLeft = cTemp;
            Keys = options_f(Keys);
            break;
        case 3:
            Keys.cDown = cTemp;
            Keys = options_f(Keys);
            break;
        case 4:
            Keys.cRight = cTemp;
            Keys = options_f(Keys);
            break;
        default:
            printf("Please enter a number from 1-4.");
            stop_f(2);
            options_f(Keys);
            break;
    }
}

The function allows me to change the contents of the characters in Keys . After having entered 0 and returning to the menu I called options_f again. Only it changed the values stored in Keys 's characters to some garbage values.

Why is that?

If you need more information on other functions I used, please ask.
I'm sorry if this seems very low level and stupid to you, but I'm trying to learn, which is why I'm asking.

Thanks :)

Answer 1

You need to return a value from the options_f() function (probably return Keys; ). This isn't even valid C code.