You can't increase the array's length if it is not declared in heap memory (see below code which first array input is asked by user and then it asks how much you want to increase array and also copy previous array elements):
#include<stdio.h>
#include<stdlib.h>
int * increasesize(int * p,int * q,int x)
{
int i;
for(i=0;i<x;i++)
{
q[i]=p[i];
}
free(p);
p=q;
return p;
}
void display(int * q,int x)
{
int i;
for(i=0;i<x;i++)
{
printf("%d \n",q[i]);
}
}
int main()
{
int x,i;
printf("enter no of element to create array");
scanf("%d",&x);
int * p=(int *)malloc(x*sizeof(int));
printf("\n enter number in the array\n");
for(i=0;i<x;i++)
{
scanf("%d",&p[i]);
}
int y;
printf("\nenter the new size to create new size of array");
scanf("%d",&y);
int * q=(int *)malloc(y*sizeof(int));
display(increasesize(p,q,x),y);
free(q);
}