/in/foo.c: In function 'main':
/in/foo.c:6:2: error: 'y1' undeclared (first use in this function)
  y1=x1+x2;
  ^~
/in/foo.c:6:2: note: each undeclared identifier is reported only once for each function it appears in
/in/foo.c:8:2: error: 'y2' undeclared (first use in this function)
  y2=x1*x2;
  ^~
/in/foo.c:10:2: error: 'y3' undeclared (first use in this function)
  y3=x1%x2;
  ^~
/in/foo.c:13:1: error: expected ';' before '}' token
 }
 ^