Language: C

#include<math.h>

int main(){
	double xa,ya,xb,yb,xc,yc,xd,yd;
	
	while(0<=scanf("%lf,%lf,%lf,%lf,%lf,%lf,%lf,%lf",&xa,&ya,&xb,&yb,&xc,&yb,&xd,&yd)){
		
	if(xc==xa){
	if((xd-xc)*(xa-xc)>0){
		printf("NO\n");
		continue;
		}else{
			printf("YES\n");
			continue;
		}
		
		if(xb==xd){
			if((xa-xb)*(xc-xb)>0){
		printf("NO\n");
		continue;
		}else{
			printf("YES\n");
			continue;
		}
		
	if((yb-(yc-ya)/(xc-xa)*(xb-xa)-ya)*(yd-(yc-ya)/(xc-xa)*(xd-xa)-ya)>0 || (ya-(yd-yb)/(xd-xb)*(xa-xb)-yb)*(yc-(yd-yb)/(xd-xb)*(xc-xb)-yb)>0){
		printf("NO\n");
		}else{
			printf("YES\n");
		}
		}
	return 0;
		}

Compiler output:
main.c: In function 'main':
main.c:6:18: error: implicit declaration of function 'scanf' [-Wimplicit-function-declaration]
    6 |         while(0<=scanf("%lf,%lf,%lf,%lf,%lf,%lf,%lf,%lf",&xa,&ya,&xb,&yb,&xc,&yb,&xd,&yd)){
      |                  ^~~~~
main.c:2:1: note: include '<stdio.h>' or provide a declaration of 'scanf'
    1 | #include<math.h>
  +++ |+#include <stdio.h>
    2 | 
main.c:6:18: warning: incompatible implicit declaration of built-in function 'scanf' [-Wbuiltin-declaration-mismatch]
    6 |         while(0<=scanf("%lf,%lf,%lf,%lf,%lf,%lf,%lf,%lf",&xa,&ya,&xb,&yb,&xc,&yb,&xd,&yd)){
      |                  ^~~~~
main.c:6:18: note: include '<stdio.h>' or provide a declaration of 'scanf'
main.c:10:17: error: implicit declaration of function 'printf' [-Wimplicit-function-declaration]
   10 |                 printf("NO\n");
      |                 ^~~~~~
main.c:10:17: note: include '<stdio.h>' or provide a declaration of 'printf'
main.c:10:17: warning: incompatible implicit declaration of built-in function 'printf' [-Wbuiltin-declaration-mismatch]
main.c:10:17: note: include '<stdio.h>' or provide a declaration of 'printf'
main.c:13:25: warning: incompatible implicit declaration of built-in function 'printf' [-Wbuiltin-declaration-mismatch]
   13 |                         printf("YES\n");
      |                         ^~~~~~
main.c:13:25: note: include '<stdio.h>' or provide a declaration of 'printf'
main.c:19:17: warning: incompatible implicit declaration of built-in function 'printf' [-Wbuiltin-declaration-mismatch]
   19 |                 printf("NO\n");
      |                 ^~~~~~
main.c:19:17: note: include '<stdio.h>' or provide a declaration of 'printf'
main.c:22:25: warning: incompatible implicit declaration of built-in function 'printf' [-Wbuiltin-declaration-mismatch]
   22 |                         printf("YES\n");
      |                         ^~~~~~
main.c:22:25: note: include '<stdio.h>' or provide a declaration of 'printf'
main.c:27:17: warning: incompatible implicit declaration of built-in function 'printf' [-Wbuiltin-declaration-mismatch]
   27 |                 printf("NO\n");
      |                 ^~~~~~
main.c:27:17: note: include '<stdio.h>' or provide a declaration of 'printf'
main.c:29:25: warning: incompatible implicit declaration of built-in function 'printf' [-Wbuiltin-declaration-mismatch]
   29 |                         printf("YES\n");
      |                         ^~~~~~
main.c:29:25: note: include '<stdio.h>' or provide a declaration of 'printf'
main.c:33:17: error: expected declaration or statement at end of input
   33 |                 }
      |                 ^
main.c:33:17: error: expected declaration or statement at end of input