Language: C

M=9999;main(n,i,j,k,a,b,c){
	double p=atan(1)*4,X[100],Y[100],x,y;
	for(;scanf("%d",&n),n;printf("%d\n",a)){
		for(i=0;i<n;i++)scanf("%lf,%lf",X+i,Y+i);
		for(a=i=0;i<n;i++){
			for(b=k=0;k<M;k++){
				x=X[i]+cos(p*k/M),y=Y[i]+sin(p*k/M);
				for(c=j=0;j<n;j++){
					if((X[j]-x)*(X[j]-x)+(Y[j]-y)*(Y[j]-y))<1+1e-7)c++;
				}
				if(b<c)b=c;
			}
			if(a<b)a=b;
		}
	}
exit(0);}

Compiler output:
main.c:1:1: warning: data definition has no type or storage class
    1 | M=9999;main(n,i,j,k,a,b,c){
      | ^
main.c:1:1: error: type defaults to 'int' in declaration of 'M' [-Wimplicit-int]
main.c:1:8: error: return type defaults to 'int' [-Wimplicit-int]
    1 | M=9999;main(n,i,j,k,a,b,c){
      |        ^~~~
main.c: In function 'main':
main.c:1:8: error: type of 'n' defaults to 'int' [-Wimplicit-int]
main.c:1:8: error: type of 'i' defaults to 'int' [-Wimplicit-int]
main.c:1:8: error: type of 'j' defaults to 'int' [-Wimplicit-int]
main.c:1:8: error: type of 'k' defaults to 'int' [-Wimplicit-int]
main.c:1:8: error: type of 'a' defaults to 'int' [-Wimplicit-int]
main.c:1:8: error: type of 'b' defaults to 'int' [-Wimplicit-int]
main.c:1:8: error: type of 'c' defaults to 'int' [-Wimplicit-int]
main.c:2:18: error: implicit declaration of function 'atan' [-Wimplicit-function-declaration]
    2 |         double p=atan(1)*4,X[100],Y[100],x,y;
      |                  ^~~~
main.c:1:1: note: include '<math.h>' or provide a declaration of 'atan'
  +++ |+#include <math.h>
    1 | M=9999;main(n,i,j,k,a,b,c){
main.c:2:18: warning: incompatible implicit declaration of built-in function 'atan' [-Wbuiltin-declaration-mismatch]
    2 |         double p=atan(1)*4,X[100],Y[100],x,y;
      |                  ^~~~
main.c:2:18: note: include '<math.h>' or provide a declaration of 'atan'
main.c:3:14: error: implicit declaration of function 'scanf' [-Wimplicit-function-declaration]
    3 |         for(;scanf("%d",&n),n;printf("%d\n",a)){
      |              ^~~~~
main.c:1:1: note: include '<stdio.h>' or provide a declaration of 'scanf'
  +++ |+#include <stdio.h>
    1 | M=9999;main(n,i,j,k,a,b,c){
main.c:3:14: warning: incompatible implicit declaration of built-in function 'scanf' [-Wbuiltin-declaration-mismatch]
    3 |         for(;scanf("%d",&n),n;printf("%d\n",a)){
      |              ^~~~~
main.c:3:14: note: include '<stdio.h>' or provide a declaration of 'scanf'
main.c:3:31: error: implicit declaration of function 'printf' [-Wimplicit-function-declaration]
    3 |         for(;scanf("%d",&n),n;printf("%d\n",a)){
      |                               ^~~~~~
main.c:3:31: note: include '<stdio.h>' or provide a declaration of 'printf'
main.c:3:31: warning: incompatible implicit declaration of built-in function 'printf' [-Wbuiltin-declaration-mismatch]
main.c:3:31: note: include '<stdio.h>' or provide a declaration of 'printf'
main.c:7:40: error: implicit declaration of function 'cos' [-Wimplicit-function-declaration]
    7 |                                 x=X[i]+cos(p*k/M),y=Y[i]+sin(p*k/M);
      |                                        ^~~
main.c:7:40: note: include '<math.h>' or provide a declaration of 'cos'
main.c:7:40: warning: incompatible implicit declaration of built-in function 'cos' [-Wbuiltin-declaration-mismatch]
main.c:7:40: note: include '<math.h>' or provide a declaration of 'cos'
main.c:7:58: error: implicit declaration of function 'sin' [-Wimplicit-function-declaration]
    7 |                                 x=X[i]+cos(p*k/M),y=Y[i]+sin(p*k/M);
      |                                                          ^~~
main.c:7:58: note: include '<math.h>' or provide a declaration of 'sin'
main.c:7:58: warning: incompatible implicit declaration of built-in function 'sin' [-Wbuiltin-declaration-mismatch]
main.c:7:58: note: include '<math.h>' or provide a declaration of 'sin'
main.c:9:80: error: expected expression before '<' token
    9 |                                         if((X[j]-x)*(X[j]-x)+(Y[j]-y)*(Y[j]-y))<1+1e-7)c++;
      |                                                                                ^
main.c:9:87: error: expected statement before ')' token
    9 |                                         if((X[j]-x)*(X[j]-x)+(Y[j]-y)*(Y[j]-y))<1+1e-7)c++;
      |                                                                                       ^
main.c:16:1: error: implicit declaration of function 'exit' [-Wimplicit-function-declaration]
   16 | exit(0);}
      | ^~~~
main.c:1:1: note: include '<stdlib.h>' or provide a declaration of 'exit'
  +++ |+#include <stdlib.h>
    1 | M=9999;main(n,i,j,k,a,b,c){
main.c:16:1: warning: incompatible implicit declaration of built-in function 'exit' [-Wbuiltin-declaration-mismatch]
   16 | exit(0);}
      | ^~~~
main.c:16:1: note: include '<stdlib.h>' or provide a declaration of 'exit'