question about pointer

Question

1.00/5 (1 vote)

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C++

#include <iostream.h>
#include <conio.h>
void main()

{

clrscr();
int *p1;
int n,i;
cout<<"Enter size of array ";
cin>>n;
p1=new int[n];
for(i=0;i<n;i++)
cin>>*p1++;
cout<<"output values "<<endl;
for(i=0;i<n;i++)
cout<<*p1++;

getch();
}

my program not give the correct output where is the mistake in logic

Posted 18-Apr-13 4:42am

ALIWAZ

Updated 18-Apr-13 4:46am

v2

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Comments

joshrduncan2012 18-Apr-13 10:44am

You need to tell us what you expect the output to be and what you are getting. We cannot guess where it is based on what we have here right now.

ALIWAZ 18-Apr-13 10:54am

i enter two values 1 and 2 in array but resut is 22 and 24

3 solutions

Solution 3

1. Problem with your output, you've changed p1 in your input, after your cin, p1 has pointed to the end of the array.

2. why still using

C++

iostream.h

It's too old... Try

C++

#include <iostream>
using namespace std;

3. remember to delete your pointer.

Posted 18-Apr-13 5:09am

gb18030

Updated 18-Apr-13 5:17am

v5

Solution 2

You need to save the pointer at teh start, and restore it when you are startign the second loop:

C#

int *p1, *pStart;
int n,i;
cout<<"Enter size of array ";
cin>>n;
pStart=new int[n];
p1 = pStart;
for(i=0;i<n;i++)
   cin>>*p1++; 
cout<<"output values "<<endl;
p1 = pStart;
for(i=0;i<n;i++)
   cout<<*p1++;
delete [] (pStart);

Note that you should also get into the habit of deleting anything you allocate when you are finished with it!

Posted 18-Apr-13 4:59am

OriginalGriff

Updated 18-Apr-13 21:16pm

v2

Comments

nv3 18-Apr-13 11:14am

You make it way to easy for these guys. I had hoped he'd get that idea himself :-)

CPallini 19-Apr-13 3:20am

5.

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nv3 · Accepted Answer · 2013-04-18T04:55:00

Solution 1

Reset the p1 pointer back to begin of the array before you start your output loop!

Posted 18-Apr-13 4:55am

nv3

Comments

ALIWAZ 18-Apr-13 10:58am

i can not please elobarate

nv3 18-Apr-13 11:16am

By looking at your last ten questions I'd say: Do yourself a favor and read a C++ book from cover to cover (or a good website might do as well). Many of the problems you are asking help about arise just because you never got the basics down.

Sergey Alexandrovich Kryukov 18-Apr-13 11:02am

Good catch, a 5.

I'll add a couple things. The loop variable i is declared above the loops, which is always bad. A loop variable for "for" statement should always be declared inside the "for" statement. And it's bad to give variables so short names.

—SA

nv3 18-Apr-13 11:14am

Thanks, Sergey!

CPallini 19-Apr-13 3:25am

I (politely :-) ) disagree on both points:
- Sometimes it is useful having a not-scoped for variable (e.g. when your loop contains a break).
- Often short variable names makes code more clean.

Sergey Alexandrovich Kryukov 19-Apr-13 11:55am

Thank you, Carlo.
#1 why? when, for example? do your mean only the loop variable of something else? maybe, but I'm just interested to know the example;
#2 it depends on what do you call short; do you think "i" or "n" is good enough?
—SA

CPallini 19-Apr-13 12:20pm

Aaaarg! it ate up almost all my long comment!
Sooner or later I am going to rewrite it.

Sergey Alexandrovich Kryukov 19-Apr-13 12:24pm

It happens and is very frustrating... :-(
—SA

CPallini 19-Apr-13 13:11pm

I wrote it in my blog page:
http://www.codeproject.com/Members/CPallini?msg=4545579#xx4545579xx

Sergey Alexandrovich Kryukov 19-Apr-13 13:56pm

Thank you, Carlo.
—SA

CPallini 19-Apr-13 3:19am

5.

nv3 19-Apr-13 3:46am

Thanks!