C++ string array & for loop doesnt work as i expected - c++

Question

#include <iostream>
using namespace std;
int main()
{
char num[10];
int a;
cout << "Odd or Even"<< endl;
for(;;)
{
cout << "Enter Number:" ;
cin >> num;
cout << endl;
for(a=9;a>=0;a--)
{
if(num[a]!='\0 && num[a]!=' ')
break;
}
if(num[a]==1 || num[a]==3 || num[a]==5 || num[a]==7 || num[a]==9)
cout << "Odd" << endl;
else
cout << "Even" << endl;
}
}
I am a rookie of C++,and I wrote a program to discriminate if a number is even or odd,
but no matter what number I enter, it only outputs "Even".
So I added these to find out when did the loop breaks:
cout << a << endl;
cout << "\"" << num[a] << "\"" << endl;
Result：
Enter Number:11
9
" "
Even
the for loop beraks when num[9]=' '? Which will lead to else and always output "Even".

Answer 1

You are confused about the character '1' and the number 1. They are different.
Instead of
if(num[a]==1 || num[a]==3 || num[a]==5 || num[a]==7 || num[a]==9)
you need
if(num[a]=='1' || num[a]=='3' || num[a]=='5' || num[a]=='7' || num[a]=='9')
Update
There is one more problems that is probably tripping you up.
num is not initialized. Zero-initialize it. Remember 0 is not the same as the character '0'.
char num[10] = {0};
Move the initialization of num inside the for loop. That will eliminate the problem of data from a previous execution of the loop from affecting the current execution of the loop.
Here's a version that works for me.
#include <iostream>
using namespace std;
int main()
{
cout << "Odd or Even"<< endl;
for(;;)
{
char num[10] = {0};
int a;
cout << "Enter Number:" ;
cin >> num;
cout << endl;
for(a=9;a>=0;a--)
{
if(num[a]!='\0' && num[a]!=' ')
break;
}
cout << num[a] << endl;
if(num[a]=='1' || num[a]=='3' || num[a]=='5' || num[a]=='7' || num[a]=='9')
cout << "Odd" << endl;
else
cout << "Even" << endl;
}
}
PS
You can replace the line
if(num[a]!='\0' && num[a]!=' ')
by
if(isdigit(num[a]))
That makes more sense to me.

Answer 2

If you are doing this with c++ there are much easier ways! Consider the following:
while (!done) {
string inputline;
getline(cin, inputline); //Now we have a string with the users input!
stringstream ss; // stringstreams help us parse data in strings!
int num; // We have a number we want to put it into.
ss >> num; // We can use the string stream to parse this number.
// You can even add error checking!
// Now to check for odd even, what do we know about even numbers? divisable by 2!
if (num % 2 == 0) // No remainder from /2
cout << Even << '\n'
else
cout << Odd << '\n'
}
see how you go with that!
Warning Untested code

Answer 3

You did a mistake (typo) here in this line..
if(num[a]!='\0 && num[a]!=' ')
it should be
if(num[a]!='\0' && num[a]!=' ')