Getting a value from a function

I play with some C programs to learn C and I have a question.

Code:

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

void array_sum(int a[], int n);

int main()
{
	int i,size;
	int *p=(int *)malloc(sizeof(int) * size);
	int buffer;
		
	
	printf("\nHow many numbers you want to enter?\n");
	scanf("%d", &size);
	printf("\nEnter %d numbers:\n", size);
	for(i = 0; i < size; i++)
	{
		scanf("%d", &buffer);
		p[i] = buffer;
	}
	
	array_sum(p, size);
			
	return 0;
}

void array_sum(int a[], int n)
{
	int i,sum;
	sum=0;
	
	for(i = 0; i < n ; i++)
	{
		sum = sum + a[i];
	}
	printf("\nHere is the sum: %d\n", sum);
}

This program works fine, my question is how I can call the sum value from the out of the function. Such as I want to take out this code from the function and used under the main()

Code:

printf("\nHere is the sum: %d\n", sum);

You can return it:

Code:

int array_sum(int a[], int n)
{
	int i,sum;
	sum=0;
	
	for(i = 0; i < n ; i++)
	{
		sum = sum + a[i];
	}

	return sum;
}

Then you can do this in main:

Code:

printf("\nHere is the sum: %d\n", array_sum(p, size));

Thanks for your reply, unfortunately I get these errors:

Code:

wk2ex.c: In function `main':
wk2ex.c:31: error: invalid use of void expression
wk2ex.c: In function `array_sum':
wk2ex.c:45: warning: `return' with a value, in function returning void

update:

Sorry I didn't see void become int ;P . The program works fine. Thanks for your help

Does it?

Because you allocate the space (using an uninitialised value for size) before you get to the prompt asking the user for the size.

Plus, read the FAQ entry on casting malloc in C.

Sorry I didn't see void become int ;P . The program works fine. Thanks for your help

But you still need to update the code to place your malloc after reading the size values. Now its just allocating memory with the junk present in size.

ssharish2005

I see thanks for your helps.

How about if there are different functions and one function returns something, how can I use that in other fuction?

From my experience there are two ways to do that. You can use globally declared variables or pointers.

Globally declared variables will be recognized by all functions so you don't have to worry about returning values as the variable will be changed in each function.

If you use pointers then you write a value to a certain memory location in a function and then can retrieve what was written there in another function.

Okay thanks I will try to use "global" and "external" variables. Pointers confuses me ;P

How about if there are different functions and one function returns something, how can I use that in other fuction?

From my experience there are two ways to do that. You can use globally declared variables or pointers.

The question is a little vague and the answer is probably somewhat misleading too. There probably is no reason to use globals (which are evil).

Pass the return value of the first function to the second function as an argument. Call the first function from the second function, etc.

Really depends on what you are doing.

Okay I want to show I want to do:

Code:

int length(node_ptr list)
{
	node_ptr current = list->next;
	int r = 0;
	while(current)
	{
		r++;
		current = current->next;
	}
	printf("\n%d items were entered to the list", r);
	return r;
}

This function returns me the value "r" and I want to use the "r" in this function. But I don't know what is the right way to do it?

Code:

void delete(int n, node_ptr list)
{
	node_ptr current = list->next;
	int number;
	printf("Enter a number to delete it from the list:");
	scanf("\n%d",&number);
	
	while(current != NULL )
	{
		if(current->data_item == number)
		{
			free(current);
			current = current -> next;
			printf("The List is modified111111\n");
			
		}
		else
		{
			current = current->next;
		}
	}
	if(current == NULL)
	{
		printf("%d is not in the list22222\n", number);
	}
}

the second function is not finished yet, i am working on it. I just wanted to show what I am asking.

Originally Posted by BoneXXX

Okay I want to show I want to do:

Code:

int length(node_ptr list)
{
	node_ptr current = list->next;
	int r = 0;
	while(current)
	{
		r++;
		current = current->next;
	}
	printf("\n%d items were entered to the list", r);
	return r;
}

This function returns me the value "r" and I want to use the "r" in this function. But I don't know what is the right way to do it?

Code:

void delete(int n, node_ptr list)
{
	node_ptr current = list->next;
	int number;
	printf("Enter a number to delete it from the list:");
	scanf("\n%d",&number);
	
	while(current != NULL )
	{
		if(current->data_item == number)
		{
			free(current);
			current = current -> next;
			printf("The List is modified111111\n");
			
		}
		else
		{
			current = current->next;
		}
	}
	if(current == NULL)
	{
		printf("%d is not in the list22222\n", number);
	}
}

the second function is not finished yet, i am working on it. I just wanted to show what I am asking.

The function that called length() would normally have a line of code like this:

Code:

number_items = length(list);

so now number_items is assigned the return value r from length(). Like always with assignments, you need to be sure number_items is an appropriate data type to receive the value of r. As you see, the name can change (and usually should), when a value is returned from a function.

Now in your call to the delete() function, just add the parameter number_items:

Code:

delete(n, list, number_items);

All your function definitions and declarations need to be updated to reflect these changes, or the compiler will vomit in your general direction.

Adak

In the delete function can I say

Code:

printf("the length was : %d ", length (r))

or do I have to do like you said? Thanks btw.

Is there any other way than changing the parameter

Code:

delete(n, list, number_items);

.
Could some one give me an example of 'extern' please? I didn't understand it from online sources that I found.