View Compilation Error

0_0_28523029_26830.cpp: In function 'int main()':
0_0_28523029_26830.cpp:18:20: error: 'flag' was not declared in this scope
                 if(flag==1)     cout<<"OK"<<endl;
                    ^
0_0_28523029_26830.cpp:20:17: error: 'flag' was not declared in this scope
                 flag=1;
                 ^