View Compilation Error

0_0_32850747_9018.cpp: In function 'int Hasha(char*)':
0_0_32850747_9018.cpp:15:18: error: 'strlen' was not declared in this scope
  int len=strlen(s);
                  ^
0_0_32850747_9018.cpp: In function 'int Hashb(char*)':
0_0_32850747_9018.cpp:25:18: error: 'strlen' was not declared in this scope
  int len=strlen(s);
                  ^