why shell sort count sort radix sort are not good code example

Example: Radix Sort in c++

#include <iostream> 
using namespace std; 
  

int getMax(int arr[], int n) 
{ 
    int mx = arr[0]; 
    for (int i = 1; i < n; i++) 
        if (arr[i] > mx) 
            mx = arr[i]; 
    return mx; 
} 
  

void countSort(int arr[], int n, int exp) 
{ 
    int output[n]; 
    int i, count[10] = { 0 }; 
  
    
    for (i = 0; i < n; i++) 
        count[(arr[i] / exp) % 10]++; 
  
   
    for (i = 1; i < 10; i++) 
        count[i] += count[i - 1]; 
  
 
    for (i = n - 1; i >= 0; i--) { 
        output[count[(arr[i] / exp) % 10] - 1] = arr[i]; 
        count[(arr[i] / exp) % 10]--; 
    } 
  
    for (i = 0; i < n; i++) 
        arr[i] = output[i]; 
} 
  


void radixsort(int arr[], int n) 
{ 

    int m = getMax(arr, n); 
  
   
    for (int exp = 1; m / exp > 0; exp *= 10) 
        countSort(arr, n, exp); 
} 
  

void print(int arr[], int n) 
{ 
    for (int i = 0; i < n; i++) 
        cout << arr[i] << " "; 
} 
  

int main() 
{ 
    int arr[] = { 170, 45, 75, 90, 802, 24, 2, 66 }; 
    int n = sizeof(arr) / sizeof(arr[0]); 
      

      radixsort(arr, n); 
    print(arr, n); 
    return 0; 
}