View Compilation Error

0_0_15365499_30188.cpp: In function 'void getnttt(char*)':
0_0_15365499_30188.cpp:110:21: error: 'strlen' was not declared in this scope
     int len=strlen(s);
                     ^
0_0_15365499_30188.cpp: In function 'int kmp(char*, char*)':
0_0_15365499_30188.cpp:134:24: error: 'strlen' was not declared in this scope
     int lena = strlen(a);
                        ^