using realloc with a for loop - c

Question

I am using realloc to allocated memory at runtime in dynamic array. Firstly, I allocated a memory with calloc with sizeof a random integer a. In my program, I have taken a=2. After that I want to store some 14 random values generated, so I have to resize the memory using realloc. I am doing the same in a for loop. FOr 1 iteration, realloc works but after that size doesnt increase and a error occurs "corruption in heap". I am not able to understand the problem. Pls help me if you can, in understanding where the problem is occuring and how to solve it.
Thanks a lot.
Below is my code:
j=j*a; //a=3
numbers = (int*) calloc(b, j); //b=14, no of elements I want to store
printf("Address:%p\n",numbers);
if (numbers == NULL)
{
printf("No Memory Allocated\n");
}
else
{
printf("Initial array size: %d elements\n", a);
printf("Adding %d elements\n", b);
}
srand( (unsigned) time( NULL ) );
for(count = 1; count <= b ; count++)
{
if(i <= j)
{
numbers[count] = rand() % 100 + 1;
printf( "Adding Value:%3d Address%p\n", numbers[count],numbers[count] );
i++;
}
if (i > j)
{
printf("Increasing array size from %d bytes to %d bytes\n",j,j*a);
j=j*a;
numbers = (int*) realloc(numbers,j);
printf("Address:%p\n",numbers);
if(numbers == NULL)
{
printf("No Memory allocated\n");
}
}
}
free(numbers);
return 0;
}

Answer 1

The initial array length (length and size are not the same) is b, not a.
Adding b elements? I don't think you are.
Arrays are zero-based in C. You loop should be for(count=0; count<b ; count++).
count is a terrible name for a loop variable. count should hold the number of elements and not be a loop variable.
It's hard to imagine what j could be. Since you use it as the element size in your call to calloc it ought be at least be a multiple of 4, the size of in int. What is it?!
The realloc doesn't seem to bear any relation to the calloc.
I'm sure there are lots of other problems. If you want more help then a clear statement of what your goal is would be required.
EDIT
It sounds like you want something like this:
int capacity = 10;
int count = 40;
int i;
int* array = (int*)malloc(capacity*sizeof(int));
for (i=0; i<count; i++)
{
if (i==capacity)
{
capacity *= 2;
array = (int*)realloc(array, capacity*sizeof(int));
}
array[i] = RandomIntInRange(1, 100);
}
free(array);
Notes:
No error checking. In production code you would check that the allocations succeeded, and the realloc done this way would leak if it failed. But there's no point confusing the message with error checking when you are still at this level of understanding.
No reading input - you can do that.
No writing output - you can do that.

Answer 2

The integer "j" is not initialized in your code, resulting in a = 0 * 3, meaning a will be zero and no memory will be allocated. The segfault is due to you not handling that numbers is NULL. Change to and set j to something meaningful
#include <stdlib.h>
#include <stdio.h>
void
main (int argc, char *argv[])
{
int a = 3;
int j = 1 * a; //a=3
int b = 14;
int *numbers = calloc (b, j); //b=14, no of elements I want to store
int count = 0, i = 0;
printf ("Address:%p\n", numbers);
if (numbers == NULL)
{
printf ("No Memory Allocated\n");
return;
}
else
{
printf ("Initial array size: %d elements\n", a);
printf ("Adding %d elements\n", b);
}
srand ((unsigned) time (NULL));
for (count = 1; count <= b; count++)
{
if (i <= j)
{
numbers[count] = rand () % 100 + 1;
printf ("Adding Value:%3d Address%p\n", numbers[count],
&(numbers[count]));
i++;
}
if (i > j)
{
printf ("Increasing array size from %d bytes to %d bytes\n", j,
j * a);
j = j * a;
numbers = (int *) realloc (numbers, j);
printf ("Address:%p\n", numbers);
if (numbers == NULL)
{
printf ("No Memory allocated\n");
}
}
}
free (numbers);
}