/in/foo.c: In function 'FindMax':
/in/foo.c:7:1: error: 'max_num' undeclared (first use in this function)
 max_num=1;
 ^~~~~~~
/in/foo.c:7:1: note: each undeclared identifier is reported only once for each function it appears in
/in/foo.c:8:12: error: expected ';' before ':' token
 for(i=1;i<n:i++)
            ^
/in/foo.c:5:9: warning: unused variable 'mx_num' [-Wunused-variable]
 int max,mx_num;
         ^~~~~~
/in/foo.c:17:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^