How to dynamically increase the array size?

Question

I've been trying to make a program that adds 2 arrays of different size. But I would like to know to to dynamically increase the array size capacity? Ex: array[4] then upgrade the size to 2 to make array[6];? EDIT: WIthout using vectors

I tried creating a new ptr but it does not work. I get the error: Read only variable is not assignable.

int *ptr2 = new int[a2.size];


            // new ptr2 copies ptr1
            for (int i=0; i<(a1.size); i++) {
                ptr2[i] = a1.ptr[i];
            }


            // we want ptr1 to point to ptr2
            for (int i=0; i<(a2.size); i++) {
                ptr2[i] += a2.ptr[i];
            }

            delete [] a1.ptr;

            a1.ptr=ptr2;

Answer 1

You can't change the size of the array, but you don't need to. You can just allocate a new array that's larger, copy the values you want to keep, delete the original array, and change the member variable to point to the new array.

1. Allocate a new[] array and store it in a temporary pointer.

2. Copy over the previous values that you want to keep.

3. Delete[] the old array.

4. Change the member variables, ptr and size to point to the new array and hold the new size.

Answer 2

   int* newArr = new int[new_size];
   std::copy(oldArr, oldArr + std::min(old_size, new_size), newArr);
   delete[] oldArr;
   oldArr = newArr;

Answer 3

#include <stdio.h>
#include <stdlib.h>
int main()
{
int *p,*q;
int i;
p=(int *)malloc(5*sizeof(int));
p[0]=3;p[1]=5;p[2]=7;p[3]=9;p[4]=11;
q=(int *)malloc(10*sizeof(int));
for(i=0;i<5;i++)
q[i]=p[i];
free(p);
p=q;
q=NULL;
for(i=0;i<5;i++)
printf("%d \n",p[i]);
return 0;
}

Answer 4

#include<bits/stdc++.h> using namespace std;

main(){

int *p = new int[5]; // locate memory in heap
int *q = new int[10];// locate memory in heap

for(int j=0; j<5;j++)
    p[j] = j;

for(int i=0; i<5;i++)
    q[i] = p[i];
    
delete []p;//Delete the old array 'p'
p = q; // Assign the pointer of 'q' to 'p'
q = NULL; // delete the location of pointer 'q'

return 0;

}

Answer 5

It may be late too answer but i'll explain some things to you..

Array Size cannot be increase because of contiguous memory allocation in the memory. For Example => The address of the every location is

arr[5] => [2001,2002,2003,2004,2005]

Now, The main problem is if you allocate it to arr[10] so, as we don't know the next location 2006 will be free . because array need to be in contiguous so, we won't be able to allocate memory

From my Suggestions use Vector or use dynamic Memory allocation in Cpp

int *old = new int[5];
int *nw = new int[10];

for (size_t i = 0; i < sizeof(old); i++)
    nw[i] = old[i];

delete []old;
old = nw;
nw = NULL;

Answer 6

You should do it using pointers and linked list https://do.nettutorials.net/lesson/how-to-increase-size-of-an-array/