View Compilation Error

0_0_20358499_3928.cpp: In function 'int main()':
0_0_20358499_3928.cpp:12:41: error: 'isalpha' was not declared in this scope
     if (sym[0] != '_' && !isalpha(sym[0]))
                                         ^
0_0_20358499_3928.cpp:19:24: error: 'isalnum' was not declared in this scope
     if (!isalnum(sym[i]) && sym[i] != '_')
                        ^