From the user's input total the odd and even numbers. input numbers in between 0 to 99

Question

#include <iostream>
using namespace std;
int main()
{
int i,t,x[20], even, odd, prime; 
cout << "Enter 20 integer numbers from 0 to 99: "<<endl;
for (i=1;i<=20;i++)
{
    cout << "Input " << i <<":";
    cin >> x[i];
}
cout << "\nPrime numbers are: " << endl ; 
prime=1;
for (i=2; i<=20 ; i++)
{
    for(t=2;t<x[i];t++)
    {
        if(x[i]%t==0)
        {
            prime=0;
        }
    }
    if(prime==1)
    {
        cout << x[i] << endl;
    }
    prime=1;
 }
 for(i=1; i<=20; i++) // this is where i have problem.
 {
    if(x[i]% 2 == 0)
    {
        even++;
    }
    else 
    {
        odd++;
    }
 }
 cout << "Number of odd numbers: " << odd << "\n";
 cout << "Number of even numbers: " << even << "\n";
 return 0 ;  
 }

When i compile it shows even (40) and odd (10) for input of 0 till 19. Where it should show even 10(including the 0) and odd (10). Im not sure where am i doing it wrongly. I hope someone can help me improve the code.

Agreed. Remove the prime finding code, has nothing to do with determining even/odd, and start stepping through with your development environment's debugger. No debugger? Stop wasting your time and get a development system with a debugger. Almost all do. — user4581301, Jul 19 '16 at 15:45
This `x[20]` and this `for (i=1;i<=20;i++)` don't go together — DimChtz, Jul 19 '16 at 15:45
`int x[20]` defines an array where valid indexes are from 0 to 19. You browse it from 1 to 20... — Thomas Ayoub, Jul 19 '16 at 15:50
owh... thanks for pointing it out. when i initialise it... it worked perfectly.. — Kugendran Subramaniyam, Jul 19 '16 at 15:58
And regarding the prime coding, its actually part of the question also.. but had problem in odd and even part. i post the whole code, just to show the whole thing. thats all.. — Kugendran Subramaniyam, Jul 19 '16 at 16:07

score 0 · Accepted Answer · edited May 23 '17 at 12:32

Variables even and odd are never set to a known value, so you are not formally allowed to read from them. Doing so invokes that most infamous Standardese concept: undefined behaviour. So the values of these variables could be right or could be wrong; the variables and all code trying to read them could be optimised entirely out of your program; or anything can happen. You cannot rely on these variables doing anything right. All attempts to read them make your program ill-formed, so now it can do anything, including things you would never have imagined.

You should search for the abundant background info about these concepts, but I like to think I made a fairly decent summary here: https://stackoverflow.com/a/38150162/2757035

Also, as Thomas points out in the comments, you appear not to understand how array indexing works: Indexes are 0-based. So, int i[20] declares 20 elements numbered from 0 to 19. You try to access index 20, which is not part of the array and hence is more undefined behaviour.

Thanks for pointing out.. Ill improve the codes. And it works now... — Kugendran Subramaniyam, Jul 19 '16 at 15:59
You're welcome, and thanks for confirming. Please consider upvoting if this was useful, and mark it as the answer if it has solved your question. — underscore_d, Jul 19 '16 at 16:01

From the user's input total the odd and even numbers. input numbers in between 0 to 99

1 Answers1