View Compilation Error

0_0_21489896_16834.cpp: In function 'bool mycmp(char*, char*)':
0_0_21489896_16834.cpp:11:13: error: 'strlen' was not declared in this scope
  if(strlen(a) != strlen(b))
             ^
0_0_21489896_16834.cpp:15:29: error: 'strlen' was not declared in this scope
  for(int i = 0; i < strlen(a); i ++){
                             ^