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

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".

Your approach is wrong, try to take an int array instead of a char array for numbers. — prince
– prince, Commented Jul 30, 2014 at 4:20
an int is four bytes and a char is only one byte,so is a number,so if i take int num[80] instead of char num[80],three-fourths of the 80*4=320 bytes will be filled with ' ' which is a waste of memory.Also if i take int ,the compiler build message will list hundreds of "argument......"which i dont want to understand. — Agritite
– Agritite, Commented Jul 30, 2014 at 15:58

R Sahu · Accepted Answer · 2014-07-30 16:03:33Z

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.

edited Jul 30, 2014 at 16:03

answered Jul 30, 2014 at 4:21

R Sahu

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1 Comment

Agritite Over a year ago

thanks for your correction , but the program still goes wrong

Fantastic Mr Fox · Accepted Answer · 2014-07-30 04:18:17Z

0

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

answered Jul 30, 2014 at 4:18

Fantastic Mr Fox

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2 Comments

Agritite Over a year ago

i know there`s a lot of ways faster ,but i still want to know the errors I made.

Fantastic Mr Fox Over a year ago

Thats fine there are plenty of answers that show you where your problem was. I am just trying to show a different solution.

rajenpandit · Accepted Answer · 2014-07-30 04:18:23Z

0

You did a mistake (typo) here in this line..

if(num[a]!='\0 && num[a]!=' ')

it should be

if(num[a]!='\0' && num[a]!=' ')

answered Jul 30, 2014 at 4:18

rajenpandit

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1 Comment

Agritite Over a year ago

thanks but that`s the typo i made in stackflow not on the editor

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