View Compilation Error

0_0_37749049_7362.cpp: In function 'int main()':
0_0_37749049_7362.cpp:55:5: error: 'flag' was not declared in this scope
     flag++;      //g为1表示该图为连通   g大于1表示有多个分图！ 
     ^
0_0_37749049_7362.cpp:60:5: error: 'flag' was not declared in this scope
     flag=0;
     ^
0_0_37749049_7362.cpp:64:39: error: 'flag' was not declared in this scope
   if(( (a==1&&b==1)||(a==0&&b==0)) && flag==1 )  puts("Ordering is possible.");
                                       ^