View Compilation Error

0_0_21197526_27942.cpp: In function 'int cmp(elem, elem)':
0_0_21197526_27942.cpp:28:32: error: 'strcmp' was not declared in this scope
     return strcmp(a.name,b.name)<0?1:0;
                                ^
0_0_21197526_27942.cpp: In function 'trie* newtrie()':
0_0_21197526_27942.cpp:35:35: error: 'memset' was not declared in this scope
     memset(t,0,sizeof(struct trie));   
                                   ^
0_0_21197526_27942.cpp: In function 'int main()':
0_0_21197526_27942.cpp:139:56: error: 'strcpy' was not declared in this scope
                     strcpy(add_str[len_add],stu[i].name);
                                                        ^
0_0_21197526_27942.cpp:144:56: error: 'strcpy' was not declared in this scope
                     strcpy(del_str[len_del],stu[i].name);
                                                        ^