Why am I getting 8s repeatedly where I should be getting 827 as output for the following code?

Question

1.00/5 (1 vote)

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C++

#include <iostream>
#include <stdlib.h>
#include <stdio.h>
using namespace std;
struct node{
int data;
struct node* next;
};
struct node* head;
void insert(int data,int n)
{
 node* temp1=new node();
 temp1->data= data;
 temp1->next=NULL;
 if (n==1){
    temp1->next=head;
    head=temp1;
    return;
 }
 node* temp2=head;
 for(int i=0;i<n-2;i++){
    temp2=temp2->next;
}
temp1->next=temp2->next;
temp2->next= temp1;
};
void print(){
node* temp=head;
while(temp!= NULL)
    cout<<temp->data<<"\n";
}
int main()
{
 head=NULL;
 insert(2,1);
 insert(7,2);
 insert(8,1);
 print();
}

What I have tried:

C++

#include <iostream>
#include <stdlib.h>
#include <stdio.h>
using namespace std;
struct node{
int data;
struct node* next;
};
struct node* head;
void insert(int data,int n)
{
 node* temp1=new node();
 temp1->data= data;
 temp1->next=NULL;
 if (n==1){
    temp1->next=head;
    head=temp1;
    return;
 }
 node* temp2=head;
 for(int i=0;i<n-2;i++){
    temp2=temp2->next;
}
temp1->next=temp2->next;
temp2->next= temp1;
};
void print(){
node* temp=head;
while(temp!= NULL)
    cout<<temp->data<<"\n";
}
int main()
{
 head=NULL;
 insert(2,1);
 insert(7,2);
 insert(8,1);
 print();
}

Posted 21-Jul-20 1:35am

Critical Fist

Updated 21-Jul-20 2:50am

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Garth J Lancaster · Accepted Answer · 2020-07-21T01:44:00

Solution 1

Think about your print code

void print(){
node* temp=head;
while(temp!= NULL)
    cout<<temp->data<<"\n";
}

.. after you've printed a node, do you think you might want to advance to the next node (hint)

void print(){
node* temp=head;
while(temp!= NULL)
    cout<<temp->data<<"\n";
    temp = ??????????
}

Posted 21-Jul-20 1:44am

Garth J Lancaster

Updated 21-Jul-20 1:46am

v2

Comments

Critical Fist 21-Jul-20 7:49am

hey thank you buddy!!!!

OriginalGriff 21-Jul-20 7:51am

Umm ... curly brackets? :laugh:

Garth J Lancaster 21-Jul-20 9:40am

:rollseyes:

OriginalGriff · Accepted Answer · 2020-07-21T01:47:00

Solution 3

Look at your print method:

C++

void print(){
    node* temp=head;
    while(temp!= NULL)
        cout<<temp->data<<"\n";
}

You don't move the temp node pointer inside the loop ...

Posted 21-Jul-20 1:47am

OriginalGriff

Comments

Critical Fist 21-Jul-20 7:49am

hey thank you buddy!!!!!

OriginalGriff 21-Jul-20 7:52am

You're welcome!

I'd strongly suggest that you start looking at the debugger for your system - it can make finding problems like this almost trivial.

Critical Fist 21-Jul-20 8:36am

i might well debugg on my own so i can improve my skills and then look for a debugger.

OriginalGriff 21-Jul-20 8:54am

No, learn to use the debugger - it gives you information on what is happening in your app while it's running, including variable contents and being able to execute you code step by step.

It's not a replacement for "manual debugging" - it's a tool which makes manual debugging a lot more effective.

For example, running that code through the debugger would have shown you that temp wasn't changing very quickly. Quicker in fact than posting a question here and waiting for an answer!

Critical Fist 21-Jul-20 8:59am

does it come along with complier or should i download it manually

OriginalGriff 21-Jul-20 9:39am

Depends. Are you using an IDE (Integrated Development Environment)?
If you edit and compile in the same app, then you are and that will include a debugger.
A (very) popular one is Visual Studio - which has a free edition:
https://visualstudio.microsoft.com/vs/community/
It's the best development environment on the planet, bar none, and has been since it was first released in 1997 (and even then, it's roots go back to the 1980s!).
If you aren't using it, you really are missing out!
If you have it and don't know how to use the debugger, Google - or even Microsoft - will help.

Patrice T · Accepted Answer · 2020-07-21T02:49:00

Quote:
Why am I getting 8s repeatedly where I should be getting 827 as output for the following code?

Your code do not behave the way you expect, or you don't understand why !

There is an almost universal solution: Run your code on debugger step by step, inspect variables.
The debugger is here to show you what your code is doing and your task is to compare with what it should do.
There is no magic in the debugger, it don't know what your code is supposed to do, it don't find bugs, it just help you to by showing you what is going on. When the code don't do what is expected, you are close to a bug.
To see what your code is doing: Just set a breakpoint and see your code performing, the debugger allow you to execute lines 1 by 1 and to inspect variables as it execute.

Debugger - Wikipedia, the free encyclopedia[^]

Mastering Debugging in Visual Studio 2010 - A Beginner's Guide[^]
Basic Debugging with Visual Studio 2010 - YouTube[^]

1.11 — Debugging your program (stepping and breakpoints) | Learn C++[^]

The debugger is here to only show you what your code is doing and your task is to compare with what it should do.

Critical Fist · Accepted Answer · 2020-07-21T01:44:00

Solution 2

ok guys i got to know of my mistake and hope people will learn from this. we should add the while statments inside brackets.

Posted 21-Jul-20 1:44am

Critical Fist