View Compilation Error

0_0_19564196_20597.cpp: In function 'void init()':
0_0_19564196_20597.cpp:18:41: error: 'memset' was not declared in this scope
 void init(){ memset(head,-1,sizeof(head)); tot=0; }
                                         ^
0_0_19564196_20597.cpp: In function 'int main()':
0_0_19564196_20597.cpp:84:31: error: 'memset' was not declared in this scope
       memset(dfn,0,sizeof(dfn));
                               ^