View Compilation Error

0_0_37104832_23496.cpp: In function 'int main()':
0_0_37104832_23496.cpp:20:21: error: 'f' was not declared in this scope
                     f=0;
                     ^
0_0_37104832_23496.cpp:24:16: error: 'f' was not declared in this scope
             if(f)
                ^