/in/foo.c: In function 'main':
/in/foo.c:4:15: error: 'b' undeclared (first use in this function)
  int a[10000];b[10000];
               ^
/in/foo.c:4:15: note: each undeclared identifier is reported only once for each function it appears in
/in/foo.c:5:9: error: 'n2' undeclared (first use in this function)
  int n1;n2;
         ^~
/in/foo.c:12:7: warning: implicit declaration of function 'FindMaxs' [-Wimplicit-function-declaration]
 int m=FindMaxs(a,n1);
       ^~~~~~~~
/in/foo.c: At top level:
/in/foo.c:18:6: warning: conflicting types for 'FindMaxs'
 void FindMaxs(int c[],int n)
      ^~~~~~~~
/in/foo.c:12:7: note: previous implicit declaration of 'FindMaxs' was here
 int m=FindMaxs(a,n1);
       ^~~~~~~~
/in/foo.c: In function 'FindMaxs':
/in/foo.c:20:6: error: 'i' undeclared (first use in this function)
  for(i=0;i<n;i++)
      ^
/in/foo.c:24:10: warning: 'return' with a value, in function returning void
  return c[k];
         ~^~~
/in/foo.c:18:6: note: declared here
 void FindMaxs(int c[],int n)
      ^~~~~~~~
/in/foo.c:27:18: warning: 'return' with a value, in function returning void
           return c[i];
                  ^
/in/foo.c:18:6: note: declared here
 void FindMaxs(int c[],int n)
      ^~~~~~~~