Counting sort correct implementation but NOT from memory

counting_sort.cpp

#include <iostream>
#include <bits/stdc++.h>

int a[] = {9,3,1,4,5,7,7,2,2};

void counting_sort(int a[], int n) {
  int radix = *std::max_element(a, a + n);

  int c[radix+1] = {};
  int b[n] = {};

  for (int i = 0; i < n; i++) {
    c[a[i]]++;
  }

  for (int j = 1; j <= radix; j++) {
    c[j] = c[j] + c[j-1];
  }

  for (int m = n-1; m > -1; m--) {
      int d = a[m];
      c[d]--;
      b[c[d]] = a[m];
  }

  for (int i = 0; i < n; i++) {
      a[i] = b[i];
  }
}

int main() {

  int n = sizeof(a)/sizeof(a[0]);

  counting_sort(a, n);
  for (int i = 0; i<n; i++) {
    std::cout << a[i] << " ";
  }
  std::cout << "\n";

  return 1;
}