View Compilation Error

0_0_21676788_8693.cpp: In function 'int Kosaraju()':
0_0_21676788_8693.cpp:41:31: error: 'memset' was not declared in this scope
     memset(flag,0,sizeof(flag));
                               ^
0_0_21676788_8693.cpp: In function 'int main()':
0_0_21676788_8693.cpp:61:38: error: 'memset' was not declared in this scope
         memset(headg,-1,sizeof(headg));
                                      ^