View Compilation Error

0_0_25183723_25128.cpp: In function 'int main()':
0_0_25183723_25128.cpp:18:42: error: 'strcmp' was not declared in this scope
         if(target==0&&strcmp(Letter,"END")==0)
                                          ^
0_0_25183723_25128.cpp:21:40: error: 'memset' was not declared in this scope
         memset(visited,0,sizeof(int)*15);
                                        ^
0_0_25183723_25128.cpp:22:26: error: 'strlen' was not declared in this scope
         len=strlen(Letter);
                          ^
0_0_25183723_25128.cpp: In function 'void dfs(int)':
0_0_25183723_25128.cpp:52:24: error: 'strlen' was not declared in this scope
     for(i=strlen(Letter)-1;i>=0;i--)
                        ^