/in/foo.c: In function 'Opp':
/in/foo.c:3:5: warning: type of 'x' defaults to 'int' [-Wimplicit-int]
 int Opp(x)
     ^~~
/in/foo.c: In function 'main':
/in/foo.c:20:2: error: expected ';' before 'printf'
  printf("%d",b);
  ^~~~~~
/in/foo.c:17:11: warning: variable 'b' set but not used [-Wunused-but-set-variable]
     int a,b;
           ^