View Compilation Error

0_0_13412905_18413.cpp: In function 'bool ishuiwen(char*)':
0_0_13412905_18413.cpp:5:19: error: 'strlen' was not declared in this scope
     int l=strlen(a);
                   ^
0_0_13412905_18413.cpp: In function 'int fun1(char*)':
0_0_13412905_18413.cpp:14:19: error: 'strlen' was not declared in this scope
     int l=strlen(a);
                   ^
0_0_13412905_18413.cpp: In function 'int fun2(char*)':
0_0_13412905_18413.cpp:26:19: error: 'strlen' was not declared in this scope
     int l=strlen(a);
                   ^