Language: C

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

struct Card {
	char suit;
	int value;
};

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

void quickSort(struct Card A[],int n, int p, int r)
{
	int q;
	if(p > r)
	{
		q = partition(A,n,p,r);
		quickSort(A,n,p,q - 1);
		quickSort(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;
			break;
		}
	}
	
	if(stable == 1) printf("Stable\n");
	else printf("Not stable\n");
	for(i = 0; i < n; i++)
	{
		printf("%s %d\n",B[i].suit,B[i].value);
	}
	
	return 0;
}

Compiler output:
main.c:10:1: error: unknown type name 'card'
   10 | card L[MAX / 2 + 2],R[MAX / 2 + 2];
      | ^~~~
main.c: In function 'merge':
main.c:17:40: error: incompatible types when assigning to type 'int' from type 'struct Card'
   17 |         for(i = 0; i < n1; i++) L[i] = A[left + i];
      |                                        ^
main.c:18:40: error: incompatible types when assigning to type 'int' from type 'struct Card'
   18 |         for(i = 0; i < n2; i++) R[i] = A[mid + i];
      |                                        ^
main.c:19:14: error: request for member 'value' in something not a structure or union
   19 |         L[n1].value = R[n2].value = SENTINEL;
      |              ^
main.c:19:28: error: request for member 'value' in something not a structure or union
   19 |         L[n1].value = R[n2].value = SENTINEL;
      |                            ^
main.c:23:24: error: request for member 'value' in something not a structure or union
   23 |                 if(L[i].value <= R[i].value)
      |                        ^
main.c:23:38: error: request for member 'value' in something not a structure or union
   23 |                 if(L[i].value <= R[i].value)
      |                                      ^
main.c:25:32: error: incompatible types when assigning to type 'struct Card' from type 'int'
   25 |                         A[k] = L[i++];
      |                                ^
main.c:27:32: error: incompatible types when assigning to type 'struct Card' from type 'int'
   27 |                         A[k] = R[j++];
      |                                ^