View Compilation Error

0_0_26953748_14688.cpp: In function 'bool c(Lstudent, Lstudent)':
0_0_26953748_14688.cpp:19:35: error: 'strcmp' was not declared in this scope
     return (strcmp(a.Lname,b.Lname)<0);
                                   ^
0_0_26953748_14688.cpp: In function 'int main()':
0_0_26953748_14688.cpp:27:37: error: 'memset' was not declared in this scope
         memset(book, 0, sizeof(book));
                                     ^
0_0_26953748_14688.cpp:56:61: error: 'strcpy' was not declared in this scope
                         strcpy(buf[count].Lname,book[b].name);
                                                             ^