problem in using new operator

Question

4.00/5 (1 vote)

See more:

C++

#include <iostream.h>
#include <conio.h>

void main()
{
    clrscr();
    int *p1,*p2,n,i;
    cout<<"Enter the size of the array ";
    cin>>n;
    p1=new int[n];
    p2=p1;
    for(i=0;i<n;i++)
        cin>>*p2++;
    p2=p1;
    for(i=n;i>0;i--)
        cout<<*p2--;
    getch();
    }

}

i input values into array created using new operator and want to print these values in reverse order but
program give wrong output

i enter
1
2
resut is 13262 instead of 2 1

Posted 24-Apr-13 3:30am

ALIWAZ

Updated 24-Apr-13 4:12am

Richard MacCutchan

v4

Add a Solution

Comments

CHill60 24-Apr-13 9:35am

It might be worth posting some sample data that you've input, what the "wrong output" was and what you were expecting to see

2 solutions

Solution 2

Without changing too much, try this instead:

C++

#include <iostream.h>
#include <conio.h>

void main()
{
    clrscr();
    int *p1,n,i;
    cout<<"Enter the size of the array ";
    cin>>n;
    p1=new int[n];
    for(i=0;i<n;i++)
        cin>>p1[i];
    for(i=n;i>0;i--)
        cout<<p1[i-1];
    delete [] p1;
    getch();
}

Regards,
Ian.

Posted 24-Apr-13 4:48am

Ian A Davidson

Updated 24-Apr-13 5:07am

v4

Comments

nv3 24-Apr-13 11:43am

Particularly for a beginner that is way better to read and understand than OP's original code. My 5.

Ian A Davidson 24-Apr-13 13:12pm

Thank you. :)

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

OriginalGriff · Accepted Answer · 2013-04-24T03:34:00

Solution 1

Look at what you are doing:
You allocate "n" elements, and then load "n" of them. Where is the pointer after the first loop?
Answer: pointing at the element after the last one.

So when you try to cout the values in the second loop, the first access is to an element that doesn't exist...

Try it on paper with a value of n=2 and you will see what I mean.

Posted 24-Apr-13 3:34am

OriginalGriff

Comments

CHill60 24-Apr-13 9:41am

My +5. Only spotted that after I'd reformatted the code - amazing what whitespace can do for the eyes

Ian A Davidson 24-Apr-13 10:44am

+4. Correct result but wrong reason. He's resetting p2=p1, so he's pointing at the beginning of the array, but then in the second loop he's doing p2-- so it's (presumably) outputting the first integer (1) and then pointing to random information before the array.
Regards,
Ian.

OriginalGriff 24-Apr-13 10:58am

Not in the original version, which was the one I answered:
"#include <iostream.h>
#include <conio.h>
void main()
{
clrscr();
int *p1,n,i;
cout<<"Enter the size of the array ";
cin>>n;
p1=new int[n];
for(i=0;i<n;i++)
cin>>*p1++;
for(i=n;i>0;i--)
cout<<*p1--; // problem is here
getch();
}

i input values into array created using new operator and print these values in reverse order but
program give wrong out put"

Ian A Davidson 24-Apr-13 11:06am

Oh yep. Sorry I "checked" that by doing a comparison, but obviously I did something wrong there. Oh dear. Changed it to a 5 :D

OriginalGriff 24-Apr-13 11:28am

Don't worry about it - I'm not going to! :laugh:

OriginalGriff 24-Apr-13 10:59am

Gah! Bloody HTML swallowing less than signs! :laugh: