View Compilation Error

0_0_36085631_16061.cpp: In function 'void insert(char*, int)':
0_0_36085631_16061.cpp:18:22: error: 'strlen' was not declared in this scope
     ll len = strlen(s);
                      ^
0_0_36085631_16061.cpp: In function 'int query(char*)':
0_0_36085631_16061.cpp:36:22: error: 'strlen' was not declared in this scope
     ll len = strlen(s);
                      ^
0_0_36085631_16061.cpp: In function 'int main()':
0_0_36085631_16061.cpp:57:28: error: 'strlen' was not declared in this scope
         ll len = strlen(str);
                            ^