View Compilation Error

0_0_13412919_16000.cpp: In function 'bool ishuiwen(char*)':
0_0_13412919_16000.cpp:6:19: error: 'strlen' was not declared in this scope
     int l=strlen(a);
                   ^
0_0_13412919_16000.cpp: In function 'int fun1(char*)':
0_0_13412919_16000.cpp:15:19: error: 'strlen' was not declared in this scope
     int l=strlen(a);
                   ^
0_0_13412919_16000.cpp: In function 'int fun2(char*)':
0_0_13412919_16000.cpp:27:19: error: 'strlen' was not declared in this scope
     int l=strlen(a);
                   ^