/in/foo.c: In function 'main':
/in/foo.c:4:11: error: 'cin' undeclared (first use in this function)
     int n;cin>>n;
           ^~~
/in/foo.c:4:11: note: each undeclared identifier is reported only once for each function it appears in
/in/foo.c:12:5: warning: implicit declaration of function 'printf' [-Wimplicit-function-declaration]
     printf("%.2f",cnt/n);
     ^~~~~~
/in/foo.c:12:5: warning: incompatible implicit declaration of built-in function 'printf'
/in/foo.c:12:5: note: include '<stdio.h>' or provide a declaration of 'printf'