I want user input of array elements and the size of an array as well but, it shows me compilation error what am i missing

Question

I want user input of array elements and the size of an array as well but, it shows me a compilation error what am i missing

    #include<stdio.h>
    #include<conio.h>
    void main(){
            int i,x,j;
            int index = 1;
            int arr[index]; // this is the place error shows up
/* error says constant expression required*/ 
                scanf("enter the number of elements: %d",&index);
            clrscr();
            for(i=0;i<index;i++){
            printf("Enter element of index no %d",i+1);
            scanf("%d",&x);
                arr[i] = x;
            }
            for(j=0;j<index;j++){
                printf("\n %d ",arr[j]);
            }
    }

Answer 1

1. Your array arr is sized to one element, changing index after the fact does not adjust the size. In other words, read index, then declare arr.
2. You try to use scanf to print a prompt, but it doesn't work that way. You need to use printf() to write out the prompt. This was actually was caused the premature exit on my system

Other bonus feedback:

3. conio.h and clrscr() are windows specific, I believe, so I left it out as I could not test it.
4. Minimized the scope of variables, and eliminated x as you can just read directly into arr[i]
5. Used unsigned instead of int when you don't want negative numbers.
6. Formatted code for readability.
7. main() by definition returns an int so changed it accordingly to resolve the warning with void main() { ...}.

Didn't fix:

8. Check the return value from scanf, mainly, because I didn't know behavior you want.
9. Check that index is reasonable sized. Variable length arrays (VLA) are dangerous as they will blow your stack if your array is too large. Stack size is OS specific and at least on Linux it's user configurable. Personally, I don't use VLA in my code and if I cannot statically allocate an array then I use heap allocation via malloc and friends.
10. You use name index for the number of elements you read. That term is normally used for loop variable like i here that indexed into an array. I suggest you rename index to n, len, or size.

#include <stdio.h>

int main() {
    unsigned index;
    printf("enter the number of elements: ");
    scanf("%u", &index);
    int arr[index];
    for(unsigned i=0; i<index; i++) {
        printf("Enter element of index no %u: ", i+1);
        scanf("%d", &arr[i]);
    }
    for(unsigned i=0; i<index; i++) {
        printf("\n %d ", arr[i]);
    }
    return 0;
}

Example session:

enter the number of elements: 3
Enter element of index no 1: 0
Enter element of index no 2: 1
Enter element of index no 3: 2

 0 
 1 
 2