try yourself |run program

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

void main(){
int n1,n2,i,*ptr,sum=0,newSum=0;
clrscr();
printf("\nEnter size of array: ");
scanf("%d",&n1);
ptr=(int*)malloc(n1 * sizeof(int));
if(ptr==NULL){
printf("\nSorry! Number of element has not given by you.");
exit(0);
}
for(i=0;i< n1;i++){
printf("\nEnter elements of array: ");
scanf("%d",ptr+i);
}
for(i=0;i< n1;i++){
printf("\n given element: %d",*(ptr+i));
sum = sum + *(ptr+i);
}
printf("\n Sum=%d",sum);
printf("\nEnter new size of array: ");
scanf("%d",&n2);
ptr = (int *)realloc(ptr, n2);
for(i=0;i< n2;i++){
printf("\nEnter new elements of array: ");
scanf("%d",ptr+i);
}
for(i=0;i< n2;i++){
printf("\n given new element: %d",*(ptr+i));
newSum = newSum + *(ptr+i);
}
printf("\n New Sum=%d",newSum);
free(ptr);
getch();
}

Program Output

Enter size of array: 5
Enter elements of array: 10
Enter elements of array: 20
Enter elements of array: 30
Enter elements of array: 40
Enter elements of array: 50
given element: 10
given element: 20
given element: 30
given element: 40
given element: 50
Sum=150
Enter new size of array: 7
Enter new elements of array: 10
Enter new elements of array: 20
Enter new elements of array: 30
Enter new elements of array: 40
Enter new elements of array: 50
Enter new elements of array: 60
Enter new elements of array: 70
given new element: 10
given new element: 20
given new element: 30
given new element: 40
given new element: 50
given new element: 60
given new element: 70
New Sum=280