Dynamic Allocating Array and Function Call

**std10093** · 12-13-2012

I am baring with you Sorinx

Everybody has been in your situation, so no problem

You have

Code:

 for (j=0;i<NUMBER_OF_GRADES;j++)

So you play with counter j, but you use counter i too. Counter i for another for loop, not for this!
So you should play only with counter j in this loop

So replace that with this

Code:

 for (j=0;j<NUMBER_OF_GRADES;j++)

**Sorinx** · 12-13-2012

Ahh yes, I noticed that and changed it, I can enter the inputs, but then afterwards it crashes.

**std10093** · 12-13-2012

It crashed in the function of the average.

In main, when you were filling the array you said

Code:

for(student=0; student<NUMBER_OF_STUDENTS; student++)
    {//for loop for populating 3 dimensional array
        for(class=0;class<NUMBER_OF_CLASSES;class++)
            {
     
        for(grade=0; grade<NUMBER_OF_GRADES; grade++)
            {
            if(grade==0){
                printf("Enter in the grade for student %d in subject %d:\n", student+1, class+1);
                scanf("%d", &array[student][class][grade]);
            }else
                scanf("%d",&array[student][class][grade]);
}
}
}

So you went through every single cell of your array.

Now in the average function you want to get the value of every single cell and add it to the sum.

Here is your function

Code:

float gradeAve(int ***c)
{
  float sum=0;
    int grade;//local variables
 
        for(grade=0; grade<NUMBER_OF_GRADES; grade++)
        {
            sum+=c[NUMBER_OF_STUDENTS][NUMBER_OF_CLASSES][NUMBER_OF_GRADES];//only takes sum of the grades and divides by number of grades
        }
     
    return (sum/NUMBER_OF_GRADES);
 
}

You have a 3D array and only one counter. This usually is wrong.

Think simple. Let's say we have a single int array of 5 elements.

Code:

int N = 5;
int array[N];

and then you want to access an element and you say

Code:

printf("%d\n",array[N]);

As you know matrices start counting from zero, thus the last element is in position N-1.
So if you say array[N] you access memory that is not yours. <--ERROR

This is pretty much what you do in the average function.

You need a tri-for loop to access all elements of the array (like you did in the main

).
So now let's write again our average function

Code:

float gradeAve(int ***c)
{
    float sum=0;
    int grade,student,class;//local variables
 
    for(student=0; student<NUMBER_OF_STUDENTS; student++)
    {//for loop for accessing 3 dimensional array
        
          for(class=0;class<NUMBER_OF_CLASSES;class++)
          {
     
                  for(grade=0; grade<NUMBER_OF_GRADES; grade++)
                 {
         
                           sum+=c[student][class][grade];
                  }
            }
      }
     
    return (sum/NUMBER_OF_GRADES);
}

Do you agree ?

**Sorinx** · 12-13-2012

Originally Posted by std10093

It crashed in the function of the average.

In main, when you were filling the array you said

Code:

for(student=0; student<NUMBER_OF_STUDENTS; student++)
    {//for loop for populating 3 dimensional array
        for(class=0;class<NUMBER_OF_CLASSES;class++)
            {
     
        for(grade=0; grade<NUMBER_OF_GRADES; grade++)
            {
            if(grade==0){
                printf("Enter in the grade for student %d in subject %d:\n", student+1, class+1);
                scanf("%d", &array[student][class][grade]);
            }else
                scanf("%d",&array[student][class][grade]);
}
}
}

So you went through every single cell of your array.

Now in the average function you want to get the value of every single cell and add it to the sum.

Here is your function

Code:

float gradeAve(int ***c)
{
  float sum=0;
    int grade;//local variables
 
        for(grade=0; grade<NUMBER_OF_GRADES; grade++)
        {
            sum+=c[NUMBER_OF_STUDENTS][NUMBER_OF_CLASSES][NUMBER_OF_GRADES];//only takes sum of the grades and divides by number of grades
        }
     
    return (sum/NUMBER_OF_GRADES);
 
}

You have a 3D array and only one counter. This usually is wrong.

Think simple. Let's say we have a single int array of 5 elements.

Code:

int N = 5;
int array[N];

and then you want to access an element and you say

Code:

printf("%d\n",array[N]);

As you know matrices start counting from zero, thus the last element is in position N-1.
So if you say array[N] you access memory that is not yours. <--ERROR

This is pretty much what you do in the average function.

You need a tri-for loop to access all elements of the array (like you did in the main

).
So now let's write again our average function

Code:

float gradeAve(int ***c)
{
    float sum=0;
    int grade,student,class;//local variables
 
    for(student=0; student<NUMBER_OF_STUDENTS; student++)
    {//for loop for accessing 3 dimensional array
        
          for(class=0;class<NUMBER_OF_CLASSES;class++)
          {
     
                  for(grade=0; grade<NUMBER_OF_GRADES; grade++)
                 {
         
                           sum+=c[student][class][grade];
                  }
            }
      }
     
    return (sum/NUMBER_OF_GRADES);
}

Do you agree ?

Lol, wow is all I can say. I know better than this

**std10093** · 12-13-2012

Originally Posted by Sorinx

Lol, wow is all I can say. I know better than this

Which means? :P

**std10093** · 12-13-2012

What I want to say, is that did you see what was the error? Did you fix it?

Also do not forget that the free function is wrong

**Sorinx** · 12-13-2012

Nah just commenting on my own stupidity, but I'm literally falling asleep, looking at free function now. never did much with malloc prior

**Sorinx** · 12-13-2012

Code:

void freeArray(int ***a) {
      
int i,j;
for(i = 0; i <=NUMBER_OF_STUDETS; i++){
    for(j = 0; j <= NUMBER_OF_CLASSES; j++){
        free(a[i][j]);
    }
    free(a[i]);
}
free(a);
    
}

**std10093** · 12-13-2012

That was a better try from the first-one posted. Again you are going out of boundaries because you start from zero in the for-loops but in the condition you have <= instead of < .

Moreover you use NUMBER_OF_GRADES instead of NUMBER_OF_CLASSES.

Here is what you should write

Code:

void freeArray(int ***a)
{
        int i,j;
        for(i = 0; i < NUMBER_OF_STUDENTS; i++){
                for(j = 0; j < NUMBER_OF_CLASSES; j++){
                        free(a[i][j]);
                }
                free(a[i]);
        }
        free(a);
}

Every time you malloc memory never forget to free it!

Every time you malloc memory take a piece of paper and draw what you are allocating

**std10093** · 12-14-2012

Pretty often I see questions about dynamic memory allocation on arrays. So I decided to write a small program that creates, fills, prints and frees a 2D array and a 3D array. In this post you will find the code for the 2D.

I something is not clear to you, just take a piece of paper and draw the memory

Allocate 2D array dynamically :

Code:

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

int **get(const int N, const int M);
void fillArray(int** array, const int N, const int M);
void printArray(int** array, const int N, const int M);
void _free(int **array, const int N);

int main(void)
{
	int **array;
	int n = 2;
	int m = 3;

	array = get(n, m);
			
	fillArray(array, n, m);

	printArray(array, n, m);

	_free(array, n);

	return 0;
}

int **get(const int N, const int M) /* Malloc the array */
{
	int i,**array;
	array=malloc(N*sizeof(int *));
    	if ( array == NULL )
    	{
		printf("Can not allocate memory. Exiting ...\n");
        	exit (0);
    	}
    	for(i=0 ; i<N ; i++)
    	{
        	array[i]=malloc( M*sizeof(int) );
        	if ( array[i] == NULL )
		{
			printf("Can not allocate memory. Exiting ...\n");
        		exit (0);
		}
    	}
    	return array;
}

void fillArray(int** array, const int N, const int M)
{
	int i, j;
	for( i = 0 ; i < N ; i++ )
        {
                for( j = 0 ; j < M ; j++ )
                {	
			array[i][j] = j;
		}
	}
}

void printArray(int** array, const int N, const int M)
{
	int i, j;
        for( i = 0 ; i < N ; i++ )
        {
                for( j = 0 ; j < M ; j++ )
                {
                        printf("array[%d][%d] = %d\n",i, j, array[i][j]);
                }
		printf("\n");
        }
}
void _free(int **array, const int N)
{
	int i;
	for(i=0 ; i<N ; i++)
    	{
        	free(array[i]);
    	}
    	free(array);
}

**std10093** · 12-14-2012

The 3D array :

Code:

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

int ***get(const int N, const int M, const int K);
void fillArray(int*** array, const int N, const int M, const int K);
void printArray(int*** array, const int N, const int M, const int K);
void _free(int ***array, const int N, const int M);

int main(void)
{
        int ***array;
	int n = 2;
	int m = 3;
	int k = 2;

        array = get(n, m, k);

        fillArray(array, n, m, k);

        printArray(array, n, m, k);

        _free(array, n, m);

        return 0;
}

int ***get(const int N, const int M, const int K) /* Malloc the array */
{
        int i, j,***array;
        array=malloc(N*sizeof(int **));
        if ( array == NULL )
        {
                printf("Can not allocate memory. Exiting ...\n");
                exit (0);
        }
        for(i=0 ; i<N ; i++)
        {
                array[i]=malloc( M*sizeof(int*) );
                if ( array[i] == NULL )
                {
                        printf("Can not allocate memory. Exiting ...\n");
                        exit (0);
                }
		for( j = 0 ; j < M ; j++ )
		{
			array[i][j] = malloc( K*sizeof(int) );
			if ( array[i][j] == NULL )
                	{
                        	printf("Can not allocate memory. Exiting ...\n");
                        	exit (0);
                	}
		}
        }
        return array;
}

void fillArray(int*** array, const int N, const int M, const int K)
{
        int i, j, k;
        for( i = 0 ; i < N ; i++ )
        {
                for( j = 0 ; j < M ; j++ )
                {
			for( k = 0 ; k < K ; k++ )
                	{
                        	array[i][j][k] = k;
			}
                }
        }
}

void printArray(int*** array, const int N, const int M, const int K)
{
        int i, j, k;
        for( i = 0 ; i < N ; i++ )
        {
                for( j = 0 ; j < M ; j++ )
                {
                        for( k = 0 ; k < K ; k++ )
                        {
                        	printf("array[%d][%d][%d] = %d\n", i, j, k, array[i][j][k]);
                        }
                }
		printf("\n");
        }
}

void _free(int ***array, const int N, const int M)
{
        int i, j;
        for(i = 0 ; i < N ; i++)
        {
		for(j = 0 ; j < M ; j++)
        	{
			free(array[i][j]);
		}
                free(array[i]);
        }
        free(array);
}

Hope that this code will help people

Dynamic Allocating Array and Function Call

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