View Compilation Error

0_0_34927048_10239.cpp: In function 'int main()':
0_0_34927048_10239.cpp:14:70: error: ISO C++ forbids comparison between pointer and integer [-fpermissive]
             if(!(ch[0]>='a'&&ch[0]<='z'||ch[0]>='A'&&ch[0]<='Z'||ch=='_'))
                                                                      ^
0_0_34927048_10239.cpp:18:76: error: ISO C++ forbids comparison between pointer and integer [-fpermissive]
                   if(!(ch[i]>='a'&&ch[i]<='z'||ch[i]>='A'&&ch[i]<='Z'||ch=='_'||ch[i]>='0'&&ch[i]<='9'))
                                                                            ^