Language: Java

import java.io.*;class Main{public static void main(String[]_)throws Exception{int i,j,k;float l[]=new float[8];BufferedReader B=new BufferedReader(new InputStreamReader(System.in));for(String s;s=B.readLine())!=null;System.out.println(k>0?"NO":"YES")){_=s.split(",");for(k=j=0;j<2;j++){for(i=0;i<8;i++)l[i]=Float.valueOf(_[(4*j+i)%8]);if(((l[0]-l[2])*(l[5]-l[1])+(l[1]-l[3])*(l[0]-l[4]))*((l[0]-l[2])*(l[7]-l[1])+(l[1]-l[3])*(l[0]-l[6]))<0)k++;}}}}

Compiler output:
Main.java:1: error: as of release 9, '_' is a keyword, and may not be used as an identifier
import java.io.*;class Main{public static void main(String[]_)throws Exception{int i,j,k;float l[]=new float[8];BufferedReader B=new BufferedReader(new InputStreamReader(System.in));for(String s;s=B.readLine())!=null;System.out.println(k>0?"NO":"YES")){_=s.split(",");for(k=j=0;j<2;j++){for(i=0;i<8;i++)l[i]=Float.valueOf(_[(4*j+i)%8]);if(((l[0]-l[2])*(l[5]-l[1])+(l[1]-l[3])*(l[0]-l[4]))*((l[0]-l[2])*(l[7]-l[1])+(l[1]-l[3])*(l[0]-l[6]))<0)k++;}}}}
                                                            ^
Main.java:1: error: ';' expected
import java.io.*;class Main{public static void main(String[]_)throws Exception{int i,j,k;float l[]=new float[8];BufferedReader B=new BufferedReader(new InputStreamReader(System.in));for(String s;s=B.readLine())!=null;System.out.println(k>0?"NO":"YES")){_=s.split(",");for(k=j=0;j<2;j++){for(i=0;i<8;i++)l[i]=Float.valueOf(_[(4*j+i)%8]);if(((l[0]-l[2])*(l[5]-l[1])+(l[1]-l[3])*(l[0]-l[4]))*((l[0]-l[2])*(l[7]-l[1])+(l[1]-l[3])*(l[0]-l[6]))<0)k++;}}}}
                                                                                                                                                                                                                 ^
Main.java:1: error: illegal start of expression
import java.io.*;class Main{public static void main(String[]_)throws Exception{int i,j,k;float l[]=new float[8];BufferedReader B=new BufferedReader(new InputStreamReader(System.in));for(String s;s=B.readLine())!=null;System.out.println(k>0?"NO":"YES")){_=s.split(",");for(k=j=0;j<2;j++){for(i=0;i<8;i++)l[i]=Float.valueOf(_[(4*j+i)%8]);if(((l[0]-l[2])*(l[5]-l[1])+(l[1]-l[3])*(l[0]-l[4]))*((l[0]-l[2])*(l[7]-l[1])+(l[1]-l[3])*(l[0]-l[6]))<0)k++;}}}}
                                                                                                                                                                                                                  ^
Main.java:1: error: ';' expected
import java.io.*;class Main{public static void main(String[]_)throws Exception{int i,j,k;float l[]=new float[8];BufferedReader B=new BufferedReader(new InputStreamReader(System.in));for(String s;s=B.readLine())!=null;System.out.println(k>0?"NO":"YES")){_=s.split(",");for(k=j=0;j<2;j++){for(i=0;i<8;i++)l[i]=Float.valueOf(_[(4*j+i)%8]);if(((l[0]-l[2])*(l[5]-l[1])+(l[1]-l[3])*(l[0]-l[4]))*((l[0]-l[2])*(l[7]-l[1])+(l[1]-l[3])*(l[0]-l[6]))<0)k++;}}}}
                                                                                                                                                                                                                                                           ^
Main.java:1: error: as of release 9, '_' is a keyword, and may not be used as an identifier
import java.io.*;class Main{public static void main(String[]_)throws Exception{int i,j,k;float l[]=new float[8];BufferedReader B=new BufferedReader(new InputStreamReader(System.in));for(String s;s=B.readLine())!=null;System.out.println(k>0?"NO":"YES")){_=s.split(",");for(k=j=0;j<2;j++){for(i=0;i<8;i++)l[i]=Float.valueOf(_[(4*j+i)%8]);if(((l[0]-l[2])*(l[5]-l[1])+(l[1]-l[3])*(l[0]-l[4]))*((l[0]-l[2])*(l[7]-l[1])+(l[1]-l[3])*(l[0]-l[6]))<0)k++;}}}}
                                                                                                                                                                                                                                                             ^
Main.java:1: error: as of release 9, '_' is a keyword, and may not be used as an identifier
import java.io.*;class Main{public static void main(String[]_)throws Exception{int i,j,k;float l[]=new float[8];BufferedReader B=new BufferedReader(new InputStreamReader(System.in));for(String s;s=B.readLine())!=null;System.out.println(k>0?"NO":"YES")){_=s.split(",");for(k=j=0;j<2;j++){for(i=0;i<8;i++)l[i]=Float.valueOf(_[(4*j+i)%8]);if(((l[0]-l[2])*(l[5]-l[1])+(l[1]-l[3])*(l[0]-l[4]))*((l[0]-l[2])*(l[7]-l[1])+(l[1]-l[3])*(l[0]-l[6]))<0)k++;}}}}
                                                                                                                                                                                                                                                                                                                                  ^
6 errors