Getting a value from a function

This is a discussion on Getting a value from a function within the C Programming forums, part of the General Programming Boards category; I play with some C programs to learn C and I have a question. Code: #include <stdio.h> #include <stdlib.h> #include ...

  1. #1
    Brak BoneXXX's Avatar
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    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);

  2. #2
    Registered User Noir's Avatar
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    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));

  3. #3
    Brak BoneXXX's Avatar
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    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
    Last edited by BoneXXX; 03-24-2007 at 10:28 PM.

  4. #4
    and the hat of wrongness Salem's Avatar
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    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.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
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  5. #5
    Registered User ssharish2005's Avatar
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    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

  6. #6
    Brak BoneXXX's Avatar
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    I see thanks for your helps.
    “Example isn't another way to teach, it is the only way to teach” Albert Einstein

  7. #7
    Brak BoneXXX's Avatar
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    How about if there are different functions and one function returns something, how can I use that in other fuction?
    “Example isn't another way to teach, it is the only way to teach” Albert Einstein

  8. #8
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    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.

  9. #9
    Brak BoneXXX's Avatar
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    Okay thanks I will try to use "global" and "external" variables. Pointers confuses me ;P
    “Example isn't another way to teach, it is the only way to teach” Albert Einstein

  10. #10
    The larch
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    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.

  11. #11
    Brak BoneXXX's Avatar
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    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&#37;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.
    “Example isn't another way to teach, it is the only way to teach” Albert Einstein

  12. #12
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    Quote Originally Posted by BoneXXX View Post
    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

  13. #13
    Brak BoneXXX's Avatar
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    In the delete function can I say

    Code:
    printf("the length was : &#37;d ", length (r))
    or do I have to do like you said? Thanks btw.
    Last edited by BoneXXX; 03-29-2007 at 02:36 AM.
    “Example isn't another way to teach, it is the only way to teach” Albert Einstein

  14. #14
    Brak BoneXXX's Avatar
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    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.
    “Example isn't another way to teach, it is the only way to teach” Albert Einstein

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