About initialize array with zero

Question

error: expected expression before { token

#include <stdio.h>

int main() {
    
    int t;
    scanf("%d",&t);
    
    while(t-->0){
        int m,n,a,b,k;
        int *arr;
        
      scanf("\n%d %d",&n,&m);
     
       arr[n]={ };
     
     
      for(int i=0;i<m;i++){
          
          scanf("\n%d %d %d",&a,&b,&k);
              
    int max=arr[0];
    for(int i=a;i<=b;i++){
        arr[i]=arr[i]+k;
        if(arr[i]>max){
            max=arr[i];
        }
    }
    printf("%d\n",max);
         
      }
      
    }
    return 0;
}

in this code, I am initializing the array to zero but it is not working and if I do this also arr[n]={} or declare the array global then also I got the error.

Answer 1

Because n is defined as a variable, there are two problems with the following statement:

int arr[n]={ };

The error on my system states
error: use of GNU empty initializer extension

If this were not a VLA, the problem could be addressed by providing an initializer:

#define n 10 //used to size a non-VLA array
...
int arr[n]={0}; //Uses constant array size, not variable,  thus can be initialized normally.

But it is a VLA, leading to the next issue, incorrect use of VLA, where the error states:
error: variable-sized object may not be initialized

Both issues can be addressed with following:

int arr[n];
memset(arr, 0, sizeof(arr));  

One final suggestion is to check the return value for the scanf() statement:

scanf("\n%d %d",&n,&m);

To ensure the correct number of items have been processed before assuming n.

int count = scanf("\n%d %d",&n,&m);
if(count == 2)
{
    int arr[n];
    memset(arr, 0, sizeof(arr);  
    ....