/in/foo.c: In function 'main':
/in/foo.c:17:6: error: 'i' undeclared (first use in this function)
  for(i=0; i<n1; i++)
      ^
/in/foo.c:17:6: note: each undeclared identifier is reported only once for each function it appears in
/in/foo.c:22:6: error: 'j' undeclared (first use in this function)
  for(j=0; j<n2; j++)
      ^
/in/foo.c:6:16: warning: variable 'n22' set but not used [-Wunused-but-set-variable]
  int n1,n11,n2,n22;
                ^~~
/in/foo.c:6:9: warning: variable 'n11' set but not used [-Wunused-but-set-variable]
  int n1,n11,n2,n22;
         ^~~