STARTING ARRAY INDEX IN DYNAMIC MEMORY ALLOCATION:

When an array is created dynamically, the array index starts with 0. So make sure you start from 0th position and use till (n-1)th position.

Even if you try using from, say, 1 to n, the array values will be valid only till (n-1)th location. Hence the data stored in n th location will be lost.

EG:

int *array,array_size=5,i;

array=(int*)malloc(sizeof(int)*array_size);     

//THIS CREATES ARRAY OF SIZE 5 FROM INDEX 0 TO 4

printf("enter the array elements\n");

//IF YOU TRY TO USE 1 TO 5 LIKE BELOW....

for(i=1;i<=array_size;i++)

{

    scanf("%d",&array[i]);

}

//THE VALUE STORED IN array[n] VALUE WILL BE LOST

printf("array elements...\n");

for(i=1;i<=5;i++)

{

    printf("%d",array[i]);

}

OUTPUT:

enter the array elements

1 2 3 4 5

array elements...

1 2 3 4

What happens is, since the allocation for array starts at 0th index and ends at (n-1)th index, array[5] location is invalid. When the input is stored in this place, it is invalid and that is why 5 is missing when displaying array elements.

The conclusion of this post is, STRICTLY use the dynamically allocated array space from 0 th index till (n-1) th index. 

Thanks for reading my blog... Hope it gives a good point :-)

Post your comments which are always welcome ;-)

DYNAMIC MEMORY ALLOCATION OF 1-D AND 2-D ARRAYS

1-D ARRAY:

FORMAT:

datatype *ptr;

int size;

ptr=(datatype*)malloc(sizeof(datatype)*size);

EG:

#include<stdio.h>

#define SIZE 3

int main()

{

    int *array,i;

    array=(int*)malloc(sizeof(int)*SIZE);

    for(i=0;i<SIZE;i++)

    {

        array[i]=0;

        printf("%d\t",array[i]);

    }

    return 0;

}

OUTPUT:

0    0    0

2-D ARRAY:

FORMAT:

datatype **ptr;

int row_size,column_size,i;

ptr=(datatype**)malloc(row_size*sizeof(datatype*));

for(i=0;i<column_size;i++)

{

    ptr[i]=(datatype*)malloc(column_size*sizeof(datatype));

}

EG:

#include<stdio.h>

#define ROW 3

#define COL 3

int main()

{

    int **array,i,j;

    array = (int**)malloc(ROW*sizeof(int*));

    for (i=0; i<ROW; i++)

    {

        array[i] = (int*)malloc(COL*sizeof(int));

    }

    for (i=0; i<ROW; i++)

    {

        for (j=0; j<COL; j++)

        {

            array[i][j]=0;

            printf("%d\t",array[i][j]);

        }

        printf("\n");

    }

    return 0;

}

OUTPUT:

0   0   0

0   0   0

0   0   0