View Compilation Error

0_0_18388217_17886.cpp: In function 'int find(int)':
0_0_18388217_17886.cpp:13:14: error: 'f' was not declared in this scope
     while(r!=f[r]) r=f[r];  
              ^
0_0_18388217_17886.cpp:16:11: error: 'f' was not declared in this scope
         j=f[k];  
           ^