lets_learn_structures_in_c_v1.c

/*

    lets_learn_structures_in_c_v1.c


    Example of work with structures in C.


    https://www.tutorialspoint.com/cprogramming/c_structures.htm

    https://www.geeksforgeeks.org/structures-c/

    https://www.learn-c.org/en/Function_arguments_by_reference


    https://www.programiz.com/c-programming/c-structures

    https://www.programiz.com/c-programming/c-structures-pointers

    https://www.programiz.com/c-programming/c-structure-function


    https://fresh2refresh.com/c-programming/c-structures/

    https://fresh2refresh.com/c-programming/c-structure-using-pointer/

    https://fresh2refresh.com/c-programming/c-nested-structure/


    You can find all my C programs at Dragan Milicev's pastebin:

    https://pastebin.com/u/dmilicev

    https://www.facebook.com/dmilicev

*/

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

#define LEFT        75      // left arrow
#define TP_NO       0       // default value, there is no contact of the rectangle with the wall

struct Rectangle {
    int num;
    float fnum;
    char ch;
    char str[100];
};

// the function receives the value of the structure and therefore cannot modify its elements
int function_arguments_by_value( struct Rectangle R )
{

    printf("\n before change in function_arguments_by_value \n");
    printf("\n R.num = %d \n", R.num );
    printf("\n R.fnum = %.2f \n", R.fnum );
    printf("\n R.ch = %c \n", R.ch );
    printf("\n R.str = %s \n\n", R.str );

    R.num = 456;            // let's change values
    R.fnum = 56.78;
    R.ch = 'B';
    strcpy( R.str, "This is new string from function_arguments_by_value()." );

    printf("\n after change in function_arguments_by_value() \n");
    printf("\n R.num = %d \n", R.num );
    printf("\n R.fnum = %.2f \n", R.fnum );
    printf("\n R.ch = %c \n", R.ch );
    printf("\n R.str = %s \n\n", R.str );

    return 0;
}

// the function gets the address of the structure and therefore can modify its elements
int function_arguments_by_reference( struct Rectangle *R )
{

    printf("\n before change in function_arguments_by_reference() \n", (*R).num );
    //printf("\n R.num = %d \n", (*R).num );
    // or, we have a shorthand syntax for that:
    printf("\n R.num = %d \n", R->num );
    printf("\n R.fnum = %.2f \n", R->fnum );
    printf("\n R.ch = %c \n", R->ch );
    printf("\n R.str = %s \n\n", R->str );

    //(*R).num = 768;

    // or, we have a shorthand syntax for that:

    R->num = 768;           // let's change values
    R->fnum = 56.78;
    R->ch = 'B';
    strcpy( R->str, "This is new string from function_arguments_by_reference()." );

    //printf("\n after change in function_arguments_by_reference() R.num = %d \n", (*R).num );

    // or, we have a shorthand syntax for that:

    printf("\n after change in function_arguments_by_reference() \n");
    printf("\n R.num = %d \n", R->num );
    printf("\n R.fnum = %.2f \n", R->fnum );
    printf("\n R.ch = %c \n", R->ch );
    printf("\n R.str = %s \n\n", R->str );

    return 0;
}


/*
Reminder:

    struct Rectangle {
        int num;
        float fnum;
        char ch;
        char str[100];
    };
*/
int main()
{
    struct Rectangle R;

    R.num = 123;                        // initial values
    R.fnum = 12.34;
    R.ch = 'A';
    strcpy( R.str, "This is string in main()" );

    printf("\n main() before function_arguments_by_value() \n");
    printf("\n R.num = %d \n", R.num );
    printf("\n R.fnum = %.2f \n", R.fnum );
    printf("\n R.ch = %c \n", R.ch );
    printf("\n R.str = %s \n\n", R.str );


    function_arguments_by_value( R );

    printf("\n main() after function_arguments_by_value() \n");
    printf("\n R.num = %d \n", R.num );
    printf("\n R.fnum = %.2f \n", R.fnum );
    printf("\n R.ch = %c \n", R.ch );
    printf("\n R.str = %s \n\n", R.str );


    printf("\n\n Notice that nothing was changed in main() \n after function_arguments_by_value() \n\n");

    function_arguments_by_reference( &R );

    printf("\n main() after function_arguments_by_reference() \n");
    printf("\n R.num = %d \n", R.num );
    printf("\n R.fnum = %.2f \n", R.fnum );
    printf("\n R.ch = %c \n", R.ch );
    printf("\n R.str = %s \n\n", R.str );

    printf("\n\n Notice that everything was changed in main() \n after function_arguments_by_reference() \n\n");


    return 0;
}