Language: C

#include <stdio.h>
#define N 100000
#define INF 1000000

struct typedef{
  char art;
  int value;
}Card_t;

struct Card_t L[N/2+2],R[N/2+2];

int n;

void merge(struct Card_t A[],int n,int l,int m,int r){
  int i,j,k;
  int n1 = m - l;
  int n2 = r - m;
  for(i=0;i<n1;i++)L[i]=A[l+i];
  for(i=0;i<n2;i++)R[i]=A[m+i];
  L[n1].value = R[n2].value = INF;
  i = j = 0;
  for(k = l;k < r;k++){
    if(L[i].value <= R[j].value){
      A[k]=L[i++];
    }else{
      A[k]=R[j++];
    }
  }
}

void mergeSort(struct Card_t A[],int l,int r){
????int m;

????if(l + 1 < r){
????????m = (l + r)/2;
????????mergeSort(A,n,l,m);
????????mergeSort(A,n,m,r);
????????merge(A,n,l,m,r);
????}
}

int partition(struct Card_t A[],int p,int r){
  int i,j;
  struct Card_t temp,s;
  s = A[r];
  i = p-1;
  for(j=p;j<r;j++){
    if(A[j].value <= s.value){
      i++;
      temp=A[i];
      A[i]=A[j];
      A[j]=temp;
    }
  }
  temp = A[i+1];
  A[i+1]=A[r];
  A[r]=temp;
  return i+1;
}

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

int main(){
int i,num,stable=1;

struct Card_t A[MAX],B[MAX];
char art;

scanf("%d",&n);

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

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

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

if(stable==1) printf("Stable\n");
else printf("Not stable\n");

for(i=0;i<n;i++){
  printf("%c %d\n",B[i].art,B[i].value);
}

return 0;
}

Compiler output:
main.c:5:8: error: expected '{' before 'typedef'
    5 | struct typedef{
      |        ^~~~~~~
main.c:8:2: warning: data definition has no type or storage class
    8 | }Card_t;
      |  ^~~~~~
main.c:8:2: error: type defaults to 'int' in declaration of 'Card_t' [-Wimplicit-int]
main.c:10:15: error: array type has incomplete element type 'struct Card_t'
   10 | struct Card_t L[N/2+2],R[N/2+2];
      |               ^
main.c:10:24: error: array type has incomplete element type 'struct Card_t'
   10 | struct Card_t L[N/2+2],R[N/2+2];
      |                        ^
main.c:14:26: error: array type has incomplete element type 'struct Card_t'
   14 | void merge(struct Card_t A[],int n,int l,int m,int r){
      |                          ^
main.c:31:30: error: array type has incomplete element type 'struct Card_t'
   31 | void mergeSort(struct Card_t A[],int l,int r){
      |                              ^
main.c: In function 'mergeSort':
main.c:32:1: error: expected expression before '?' token
   32 | ????int m;
      | ^
main.c:34:1: error: expected expression before '?' token
   34 | ????if(l + 1 < r){
      | ^
main.c: At top level:
main.c:42:29: error: array type has incomplete element type 'struct Card_t'
   42 | int partition(struct Card_t A[],int p,int r){
      |                             ^
main.c: In function 'partition':
main.c:44:17: error: storage size of 'temp' isn't known
   44 |   struct Card_t temp,s;
      |                 ^~~~
main.c:44:22: error: storage size of 's' isn't known
   44 |   struct Card_t temp,s;
      |                      ^
main.c: At top level:
main.c:61:30: error: array type has incomplete element type 'struct Card_t'
   61 | void quickSort(struct Card_t A[], int p, int r){
      |                              ^
main.c: In function 'quickSort':
main.c:63:3: error: 'q' undeclared (first use in this function)
   63 |   q = partition(A, p, r);
      |   ^
main.c:63:3: note: each undeclared identifier is reported only once for each function it appears in
main.c:63:17: error: type of formal parameter 1 is incomplete
   63 |   q = partition(A, p, r);
      |                 ^
main.c:64:13: error: type of formal parameter 1 is incomplete
   64 |   quickSort(A, p, q-1);
      |             ^
main.c:65:13: error: type of formal parameter 1 is incomplete
   65 |   quickSort(A, q+1, r);
      |             ^
main.c: In function 'main':
main.c:72:17: error: 'MAX' undeclared (first use in this function)
   72 | struct Card_t A[MAX],B[MAX];
      |                 ^~~
main.c:80:25: error: 'v' undeclared (first use in this function)
   80 |   A[i].value=B[i].value=v;
      |                         ^
main.c:83:11: error: type of formal parameter 1 is incomplete
   83 | mergeSort(A,0,n);
      |           ^
main.c:84:11: error: type of formal parameter 1 is incomplete
   84 | quickSort(B,0,n-1);
      |           ^