foo.cpp:5:41: error: expected ',' or '...' before '?' token
 bool judge(string s1,string s2,string s3?int n)  
                                         ^
foo.cpp: In function 'bool judge(std::string, std::string, std::string)':
foo.cpp:9:19: error: 'n' was not declared in this scope
     for(int i=0;i<n;i++){  
                   ^
foo.cpp: In function 'int main()':
foo.cpp:22:7: error: 'a' was not declared in this scope
  cin>>a;
       ^
foo.cpp:23:7: error: 'b' was not declared in this scope
  cin>>b;
       ^
foo.cpp:24:7: error: 'c' was not declared in this scope
  cin>>c;
       ^
foo.cpp:25:21: error: too many arguments to function 'bool judge(std::string, std::string, std::string)'
  if(judge(s1,s2,s3,n))
                     ^
foo.cpp:5:6: note: declared here
 bool judge(string s1,string s2,string s3?int n)  
      ^
foo.cpp:27:26: error: too many arguments to function 'bool judge(std::string, std::string, std::string)'
  else if(judge(s2,s1,s3,n))
                          ^
foo.cpp:5:6: note: declared here
 bool judge(string s1,string s2,string s3?int n)  
      ^
foo.cpp:29:26: error: too many arguments to function 'bool judge(std::string, std::string, std::string)'
  else if(judge(s3,s2,s1,n))
                          ^
foo.cpp:5:6: note: declared here
 bool judge(string s1,string s2,string s3?int n)  
      ^