Language: C++

#include<stdio.h>
#define MAX 100000
#define SENTINEL 2000000000

struct Card {
  char suit;
  int value;
};

struct Card L[MAX / 2 + 2], R[MAX / 2 + 2];

void merge(struct Card A[], int n, int left, int mid, int right) {
  int i, j, k;
  int n1 = mid - left;
  int n2 = right - mid;
  for ( i = 0; i < n1; i++ ) L[i] = A[left + i];
  for ( i = 0; i < n2; i++ ) R[i] = A[mid + i];
  L[n1].value = R[n2].value = SENTINEL;
  i = j = 0;
  for ( k = left; k < right; k++ ) {
    if ( L[i].value <= R[j].value ) {
      A[k] = L[i++];
    } else {
      A[k] = R[j++];
    }
  }
}

void mergeSort(struct Card A[], int n, int left, int right) {
  int mid;
  if ( left + 1 < right ) {
    mid = (left + right) / 2;
    mergeSort(A, n, left, mid);
    mergeSort(A, n, mid, right);
    merge(A, n, left, mid, right);
  }
}

int partition(struct Card A[], int n, int p, int r) {
  int t;
  int x = A[r].value;
  int i = p - 1;
  for ( int j = p; j < r; j++ ) {
    if ( A[j].value < x ) {
      i++;
      t = A[i]; A[i] = A[j]; A[j] = t;
    }
  }
  t = A[i + 1]; A[i + 1] = A[r]; A[r] = t;
  return i++;
}

void quickSort(struct Card A[], int n, int p, int r) {
  int q;
  if ( p < r ) {
    q = partition(A, n, p, r);
    partition(A, n, p, q - 1);
    partition(A, n, q + 1, r);
  }
}

int main() {
  int n, i, v;
  struct Card A[MAX], B[MAX];
  char S[10];
  int stable = 1;

  scanf("%d", &n);

  for ( i = 0; i < n; i++) {
    scanf("%s %d", S, &v);
    A[i].suit = B[i].suit = S[0];
    A[i].value = B[i].value = v;
  }

  mergeSort(A, n, 0, n);
  quickSort(B, n, 0, n - 1);

  for ( i = 0; i < n; i++ ) {
    if ( A[i].suit != B[i].suit ) stable = 0;
  } 

  if ( stable == 1) print("Stable\n");
  else printf("Not stable\n");
  for ( i = 0; i < n; i++ ) {
    printf("%c %d\n", B[i].suit, B[i].value);
  }

  return 0;
}


Compiler output:
a.cc: In function 'int partition(Card*, int, int, int)':
a.cc:46:14: error: cannot convert 'Card' to 'int' in assignment
   46 |       t = A[i]; A[i] = A[j]; A[j] = t;
      |           ~~~^
      |              |
      |              Card
a.cc:46:37: error: no match for 'operator=' (operand types are 'Card' and 'int')
   46 |       t = A[i]; A[i] = A[j]; A[j] = t;
      |                                     ^
a.cc:5:8: note: candidate: 'constexpr Card& Card::operator=(const Card&)'
    5 | struct Card {
      |        ^~~~
a.cc:5:8: note:   no known conversion for argument 1 from 'int' to 'const Card&'
a.cc:5:8: note: candidate: 'constexpr Card& Card::operator=(Card&&)'
a.cc:5:8: note:   no known conversion for argument 1 from 'int' to 'Card&&'
a.cc:49:14: error: cannot convert 'Card' to 'int' in assignment
   49 |   t = A[i + 1]; A[i + 1] = A[r]; A[r] = t;
      |       ~~~~~~~^
      |              |
      |              Card
a.cc:49:41: error: no match for 'operator=' (operand types are 'Card' and 'int')
   49 |   t = A[i + 1]; A[i + 1] = A[r]; A[r] = t;
      |                                         ^
a.cc:5:8: note: candidate: 'constexpr Card& Card::operator=(const Card&)'
    5 | struct Card {
      |        ^~~~
a.cc:5:8: note:   no known conversion for argument 1 from 'int' to 'const Card&'
a.cc:5:8: note: candidate: 'constexpr Card& Card::operator=(Card&&)'
a.cc:5:8: note:   no known conversion for argument 1 from 'int' to 'Card&&'
a.cc: In function 'int main()':
a.cc:83:21: error: 'print' was not declared in this scope; did you mean 'printf'?
   83 |   if ( stable == 1) print("Stable\n");
      |                     ^~~~~
      |                     printf