View Compilation Error

0_0_4138668_19396.cpp: In function `int check(char*)':
0_0_4138668_19396.cpp:5: error: `strlen' undeclared (first use this function)
0_0_4138668_19396.cpp:5: error: (Each undeclared identifier is reported only once for each function it appears in.)
0_0_4138668_19396.cpp:9: error: `isdigit' undeclared (first use this function)
0_0_4138668_19396.cpp:11: error: `isalpha' undeclared (first use this function)