/* Input */ codes stops working when I modularize the code?

Example code 1 - [ OK ]
3Wah7S4K - Pastebin.com

But when I try to modularize the /* Input */ codes then I get all sorts of warnings and errors. I managed to fix most of them but get stuck here where it complains about my n variable.

Example code 2 - [ Error ]
v4HKi1ae - Pastebin.com

This is not the only warning but it's the first warning at this point.

Code:

---

  C:\Test_Array\example_code_02.c In function `input':
90 C:\Test_Array\example_code_02.c [Warning] passing arg 1 of `calloc' makes integer from pointer without a cast

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Code:

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void input(double *array, double *array_copy, int *n)
{
    int i;
 //    double * array = NULL;
 //    double * array_copy = NULL;
 
    printf("How many numbers do you want to input? --> "); scanf("%d",&n);
    // calloc = Memory allocation for array.

    array = calloc(n, sizeof *array);
    array_copy = calloc(n, sizeof *array_copy);

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n is a pointer variable, so you must dereference the pointer variable to get the value to which it's pointing:

Code:

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array = calloc(*n, sizeof *array);
array_copy = calloc(*n, sizeof *array_copy);

---

If you've got errors, then post the errors...we're not clairvoyant.

Thanks for pointing me in the right direction. :) I googled and got help from Binky Pointer Fun Video along with the reading material Pointer Basics.
Now I finally grasp the concept of pointers I think, thanks to the author differentiating and terming the words Pointers & Pointees.

Here's the simplest pointer code I could find. Example code 3 works but when I try to modularize the same code into its own function in Example code 4 then it no longer works.
Can somebody show me how to do this the correct way?


Example code 3 - [ OK ]

Code:

---

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

void input(int *, int *);


//int main(int argc, char *argv[])
int main(void)
{
// 1
        int* x;
        int* y;


// 2
        x = malloc(sizeof(int));
        y = malloc(sizeof(int));


// 3
    input(x, y);


// 4
        *x = 1;
        *y = 3;


// 5
//        x = y;


// 6
    printf("x = %d\n", *x);
    printf("y = %d\n\n", *y);

    system("PAUSE");       
    return 0;
}

/*************
* Functions
*************/
/* ___________________________________________________________________________*/
/* Input */
void input(int* x, int* y)
{



}
/* ___________________________________________________________________________*/

---

Example code 4 - [ Error ]

Code:

---

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

void input(int *, int *);


//int main(int argc, char *argv[])
int main(void)
{
// 1
        int* x;
        int* y;


// 2
//        x = malloc(sizeof(int));
//        y = malloc(sizeof(int));


// 3
    input(x, y);


// 4
//        *x = 1;
//        *y = 3;


// 5
//        x = y;


// 6
    printf("x = %d\n", *x);
    printf("y = %d\n\n", *y);

    system("PAUSE");       
    return 0;
}

/*************
* Functions
*************/
/* ___________________________________________________________________________*/
/* Input */
void input(int* x, int* y)
{
// 1
//        int* x;
//        int* y;


// 2
        x = malloc(sizeof(int));
        y = malloc(sizeof(int));


// 4
        *x = 1;
        *y = 3;


// 5


}



/* ___________________________________________________________________________*/

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I suggest a simpler solution that does not use dynamic memory allocation:

Code:

---

#include <stdio.h>

void input(int* x, int* y);

int main(void)
{
    int x;
    int y;

    input(&x, &y);

    printf("x = %d\n", x);
    printf("y = %d\n\n", y);

    return 0;
}

void input(int* x, int* y)
{
    /* Replace these with actual input reading functionality */
    *x = 1;
    *y = 3;
}

---

Thanks laserlight that code looks cool. :cool:
Could somebody also show me how the same code, should be solved using the dynamic-memory-allocation-technique?

These two ways of dealing with Pointers & Pointees confuses the heck out of me. My teacher mixes these two kind of coding styles without explaining when he uses which in his newbie materials. So I have a hard time understanding this subject, when tutorials I google does the same mistake also. :confused:


source: Pointer Basics

Quote:

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Another way to play with pointers in C (or C++) is using the ampersand (&) operator to compute a pointer to local memory in the stack. However, pointees dynamically allocated in the heap are the most common, so that's what we show.

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Static memory allocation:

int x[100]; /* this memory is allocated on the stack */

Dynamic memory allocation:

int *x;

x = malloc(sizeof(int) * 100); /* this memory is allocated on the heap */

So why doesn't my Dynamic-memory-allocation code above connect when I modularize it into a function? It works when I run it without using a function. :confused:

Example code 4 - [ Error ]
You can find the complete code in a previous post above.


Also why does allocation of pointers look different in 3 different ways when I look at C study materials? Triple confusion. :confused:

int* x;
int *x;
int * x;

Quote:

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Originally Posted by Witch

So why doesn't my Dynamic-memory-allocation code above connect when I modularize it into a function? It works when I run it without using a function.

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The problem is that you are trying to change a pointer (two of them, actually). This means that you need to pass a pointer to a pointer, e.g.,

Code:

---

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

void input(int** x, int** y);

int main(void)
{
    int* x;
    int* y;

    input(&x, &y);

    printf("x = %d\n", *x);
    printf("y = %d\n\n", *y);

    free(x);
    free(y);

    return 0;
}

void input(int** x, int** y)
{
    *x = malloc(sizeof(**x));
    *y = malloc(sizeof(**y));

    /* Assume that malloc does not return a null pointer
    * Replace these with actual input reading functionality */
    **x = 1;
    **y = 3;
}

---

Quote:

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Originally Posted by Witch

Also why does allocation of pointers look different in 3 different ways when I look at C study materials? Triple confusion.

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Except in some cases, e.g., within string literals, whitespace is not significant. You should be aware of this when you read those material, but for your own code you should pick one style and stick with it.

Thanks laserlight that code rocks! :D