Pass array through functions

This is a discussion on Pass array through functions within the C Programming forums, part of the General Programming Boards category; Hey, i would like to know how exactly you pass an array from one function to another. so say i ...

  1. #1
    Shibby willc0de4food's Avatar
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    Pass array through functions

    Hey, i would like to know how exactly you pass an array from one function to another. so say i generated 10 random numbers and stored them in an integer array, how would i return this to a function. and then also, how would i pass this array directly to another function? thanks

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    Code:
    #include <stdio.h>
    
    void foo(int *array, int arraysize)
    {
    	int	i;
    
    	/* Print the contents of the array */
    	for(i = 0; i < arraysize; i++)
    		printf("Array index %d = %d\n", i, array[i]);
    }
    
    int main(int argc, char* argv[])
    {
    	int array[10], i, size;
    
    	/* Get the size of the array */
    	size = sizeof(array) / sizeof(int);
    
    	/* Fill the array with some data */
    	for(i = 0; i < size; i++)
    		array[i] = i;
    
    	/* Call a function, passing it the array, and its size */
    	foo(array, size);
    
    	return 0;
    }

  3. #3
    Shibby willc0de4food's Avatar
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    thank you very much.
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  4. #4
    Shibby willc0de4food's Avatar
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    so what if i wanted to get the numbers in the array generated randomly and then returned? i know that foo would have to be an int instead of void..
    Code:
    array = foo(user_designated_number_for_size);
    ?
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    Code:
    int* foo(int *array, int arraysize)
    {
    	int	i;
    
    	/* Print the contents of the array */
    	for(i = 0; i < arraysize; i++)
    		printf("Array index %d = %d\n", i, array[i]);
    
    	return array;
    }

  6. #6
    Shibby willc0de4food's Avatar
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    hmm.. that helps. but i was thinking a function more like this:
    Code:
    int* generate(int number)
    {
         int maxrand = 70, random_number[255], counter = 0;
         /* Clear the menu from the screen, multiple menu's annoy me */
         system("cls");
         
         /* create random number */
         do {
         srand( (unsigned)time( NULL ));
         random_number[counter] = rand() % maxrand;
         ++counter;
         } while (counter < number);
         printf("\nRandom number generation completed.\n\n");
         
         /* send the random number back to main */
         return random_number;
    }
    i'm getting an error saying that the functions returns the address of a local variable which makes sense. so would this be one of those extreme cases to use global variables? because its seeming that they would make this A LOT easier. if not, why? whats bad about global variables? thanks
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  7. #7
    and the hat of int overfl Salem's Avatar
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    Changing 1 line in bithub's code
    Code:
    int* foo(int *array, int arraysize)
    {
    	int	i;
    
    	/* fill the contents of the array with random numbers */
    	for(i = 0; i < arraysize; i++)
    		array[i] = rand() % maxrand;
    
    	return array;
    }
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
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  8. #8
    ATH0 quzah's Avatar
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    Yeah except you still can't make an assignment as they're trying to do:

    Quote Originally Posted by willc0de4food
    so what if i wanted to get the numbers in the array generated randomly and then returned? i know that foo would have to be an int instead of void..
    Code:
    array = foo(user_designated_number_for_size);
    ?
    You cannot assign arrays. In other words, if this is what you're trying to do, you can't:
    Code:
    int *foo( ... )
    {
        ...
    }
    
    ...
    
    int main( void )
    {
        int array[ BUFSIZ ];
    
        array = foo( ... );
    
        return 0;
    }
    You cannot assign arrays entire values like that. If 'array' were a pointer that you had, in function foo, malloced and filled, then you could return it:
    Code:
    int *foo( ... )
    {
        int *bar;
    
        bar = malloc( somesize );
        ...
    
       return bar;
    }
    
    int main( void )
    {
        int *baz;
    
       baz = foo( ... );
       ...
    
        free( baz );
        return 0;
    }
    This is legal. The first example isn't. Because again, you cannot use the assignment operator (other than at declaration) to assign values to entire arrays.

    Quzah.
    Hope is the first step on the road to disappointment.

  9. #9
    Shibby willc0de4food's Avatar
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    what does malloc do? also, what does calloc do?

    and what about global variables? why are they bad? lol thanks.
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    malloc and calloc allocate memory. You really should read some C tutorials before you go any further.

  11. #11
    Shibby willc0de4food's Avatar
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    lol ok. but that still doesn't say anything about global variables thats what i would really like to know about. lol
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  12. #12
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    There's nothing wrong with global variables, but use them only when you have to. If you can accomplish the same thing easily without using a global variable, then it's considered better programming style to do it that way.

  13. #13
    Shibby willc0de4food's Avatar
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    iIi c...well what if a global variable would make everything 50% easier? that could be an exaggeration, but i belive it would simplify things greatly - especially considering my skill level is that of a novice.
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  14. #14
    Just Lurking Dave_Sinkula's Avatar
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    Quote Originally Posted by willc0de4food
    well what if a global variable would make everything 50% easier? that could be an exaggeration, but i belive it would simplify things greatly - especially considering my skill level is that of a novice.
    Using global variables can make things appear to be 50% easier as a novice. Unfortunately, this little habit grows with you and when you have more complicated code, it can make things 500% harder to debug (remember that 89.6% of all statistics are made up on the spot). This tradeoff is one of the reasons why the recommendation against using global variables is so prevalent. It also detracts from learning to think in terms of encapsulation and against properly choosing data types.
    7. It is easier to write an incorrect program than understand a correct one.
    40. There are two ways to write error-free programs; only the third one works.*

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