why I can't change the gloable variable

[Sakula]

#define MAX 20

/* includes */
#include<iostream.h>
#include<stdio.h>
#include<malloc.h>
#include<string.h>
struct Student
{
int number;
int age;
int male;
char name[20];
Student * next;

};
Student * Create();
void ShowList(Student * g_head);
Student * Delete(Student * g_head, int age);

Student * g_head;
Student * Create()
{
Student * pS;
Student * pEnd;
pS=new Student;
cout<<"please input number,age ,male and name"<<endl;
cin>>pS->number>>pS->age>>pS->male;
gets(pS->name);
g_head=NULL;
pEnd=pS;
while(pS->number!=0)
{
if(g_head==NULL)
g_head = pS;
else
pEnd->next=pS;
pEnd=pS;
pS=new Student;
cout<<"please input number,age , male and name"<<endl;

cin>>pS->number>>pS->age>>pS->male;
gets(pS->name);
}
pEnd->next=NULL;
delete pS;
return (g_head);

}
void ShowList(Student * g_head)
{
cout<<"now the items of list are \n";

while(g_head)
{
cout<<g_head->number<<" "<<g_head->age<<"
"<<g_head->male<<"
"<<g_head->name<<endl;
g_head=g_head->next;
}

}
Student * Delete(Student * g_head, int age)
{
Student *p=NULL;
p=new Student;
if(!g_head)
{
cout<<"\nList null!\n";
return NULL;
}
if(g_head->age==age)
{
p=g_head;
g_head=g_head->next;
delete p;
cout<<age<<"the g_head of list has been deleted\n";
return g_head;
}
for(Student * pGuard=g_head; pGuard->next;pGuard=pGuard->next)
{
if(pGuard->next->age==age)
{
p=pGuard->next;
pGuard->next=p->next;
delete p;
cout<<age<<"has been deleted\n";
return g_head;
}
}

cout<<age<<"is not found! \n";

}
void main()
{
int age=0;

g_head=Create();
cout<<"now the list are \n";

ShowList(g_head);
cout<<"please input the age you want to delete : \n";
cin>>age;

Delete(g_head,age);

ShowList(g_head);
}
when i delete the head of the linked list,it will be crupt!
I debug this program and find the gloable variable g_head doesn't be
changed by Delete( ). I don't know why this happen.

[Walter Roberson]

In article <11**********************@e3g2000cwe.googlegroups. com>,
Sakula <jx*******@gmail.comwrote:

>/* includes */

>#include<iostream.h>

That's a C++ program. Please try a C++ newsgroup. C++ is a different
language than C and has some important differences from C.
--
Is there any thing whereof it may be said, See, this is new? It hath
been already of old time, which was before us. -- Ecclesiastes

[Martin Ambuhl]

Sakula wrote:
[...]

#include<iostream.h>

This header does not exist in either C or C++. The (offtopic) C++
language has a simliarly named <iostreamheader. Similar functionality
in the (topical) C language uses the <stdio.hheader.

#include<malloc.h>

This header does not exist in either C or C++. In the C language, the
only one topical here, malloc is prototyped in <stdlib.h>

struct Student
{
int number;
int age;
int male;
char name[20];
Student * next;

^^^^^^^
This is not legal in C without a prior typedef.

};
Student * Create();

^^^^^^^
This is not legal in C without a prior typedef.
[...]

void main()

^^^^
This is not legal in C or C++.

etc.

You are clearly lost. Not only is your code not C, which would be
topical in comp.lang.c, you have done the nearly impossible: written
gobbledygook that not even a (non-topical) C++ compiler would accept as
standard C++.

If you want to post C++ questions, do so in the appropriate newsgroup.
But learn something about C++ first: if you can't even write a legal
definition for main, it's time for you to start over at page 1.

[Richard Heathfield]

Walter Roberson said:

In article <11**********************@e3g2000cwe.googlegroups. com>,
Sakula <jx*******@gmail.comwrote:

>>/* includes */

>>#include<iostream.h>

That's a C++ program.

You may be right (although in fact you probably are not), but the evidence
cited above is insufficient to demonstrate this. C implementations are free
to ship headers by that name.

--
Richard Heathfield
"Usenet is a strange place" - dmr 29/7/1999
http://www.cpax.org.uk
email: rjh at above domain (but drop the www, obviously)

[Walter Roberson]

In article <o4******************************@bt.com>,
Richard Heathfield <in*****@invalid.invalidwrote:

>Walter Roberson said:

>In article <11**********************@e3g2000cwe.googlegroups. com>,
Sakula <jx*******@gmail.comwrote:

>>>/* includes */

>>>#include<iostream.h>

>That's a C++ program.

>You may be right (although in fact you probably are not), but the evidence
cited above is insufficient to demonstrate this. C implementations are free
to ship headers by that name.

It was a C++ program. It had numerous cout uses, including at least
one cout <<" " which is not valid in C (wrong type of argument for <<)
--
If you lie to the compiler, it will get its revenge. -- Henry Spencer

[CBFalconer]

Richard Heathfield wrote:

Walter Roberson said:

>Sakula <jx*******@gmail.comwrote:

>>/* includes */

#include<iostream.h>

That's a C++ program.

You may be right (although in fact you probably are not), but the
evidence cited above is insufficient to demonstrate this. C
implementations are free to ship headers by that name.

Well, later on he is doing such things as calling an undeclared
function 'new', and doing shifts into the undeclared variable
cout. You may want to reconsider your probabilities.

--
Chuck F (cbfalconer at maineline dot net)
Available for consulting/temporary embedded and systems.
<http://cbfalconer.home.att.net>

--
Posted via a free Usenet account from http://www.teranews.com
Warning: Do not use Ultimate-Anonymity
They are worthless spammers that are running a scam.

[Richard Heathfield]

Walter Roberson said:

In article <o4******************************@bt.com>,
Richard Heathfield <in*****@invalid.invalidwrote:

>>Walter Roberson said:

>>In article <11**********************@e3g2000cwe.googlegroups. com>,
Sakula <jx*******@gmail.comwrote:

>>>>/* includes */

>>>>#include<iostream.h>

>>That's a C++ program.

>>You may be right (although in fact you probably are not), but the evidence
cited above is insufficient to demonstrate this. C implementations are
free to ship headers by that name.

It was a C++ program.

That's debatable, given the inclusion of <iostream.h>, which is not a
standard C++ header.

--
Richard Heathfield
"Usenet is a strange place" - dmr 29/7/1999
http://www.cpax.org.uk
email: rjh at above domain (but drop the www, obviously)

[Richard Heathfield]

CBFalconer said:

Richard Heathfield wrote:

>Walter Roberson said:

>>Sakula <jx*******@gmail.comwrote:

/* includes */

#include<iostream.h>

That's a C++ program.

You may be right (although in fact you probably are not), but the
evidence cited above is insufficient to demonstrate this. C
implementations are free to ship headers by that name.

Well, later on he is doing such things as calling an undeclared
function 'new', and doing shifts into the undeclared variable
cout. You may want to reconsider your probabilities.

You may want to re-read my reply, and especially the first sentence thereof.

--
Richard Heathfield
"Usenet is a strange place" - dmr 29/7/1999
http://www.cpax.org.uk
email: rjh at above domain (but drop the www, obviously)

[Michal Nazarewicz]

"Sakula" <jx*******@gmail.comwrites:

[cut]

Student * g_head;

[cut]

Student * Delete(Student *g_head, int age) {

[cut]

}

void main() {

[cut]

Delete(g_head, age);

[cut]

}

when i delete the head of the linked list,it will be crupt!
I debug this program and find the gloable variable g_head doesn't be
changed by Delete( ). I don't know why this happen.

That's because Delete() has it's own g_head variable passed as an
argument which /shadows/ the global g_head variable. If you want to
be able to modify passed argument you'll have to change definition of
Delete to Student *Delete(Student **g_head, int age) and change the
program approprietly.

BTW. your post doesn't belong here as you are writting in C++ not
C (the "new" operator revelas that).

--
Best regards, _ _
.o. | Liege of Serenly Enlightened Majesty of o' \,=./ `o
..o | Computer Science, Michal "mina86" Nazarewicz (o o)
ooo +--<mina86*tlen.pl>--<jid:mina86*jabber.org>--ooO--(_)--Ooo--

[CBFalconer]

Richard Heathfield wrote:

CBFalconer said:

>Richard Heathfield wrote:

>>Walter Roberson said:
Sakula <jx*******@gmail.comwrote:

/* includes */
>
#include<iostream.h>

That's a C++ program.

You may be right (although in fact you probably are not), but
the evidence cited above is insufficient to demonstrate this. C
implementations are free to ship headers by that name.

Well, later on he is doing such things as calling an undeclared
function 'new', and doing shifts into the undeclared variable
cout. You may want to reconsider your probabilities.

You may want to re-read my reply, and especially the first
sentence thereof.

Which is quoted in its entirety above. I see nothing new.

--
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http://www.netmeister.org/news/learn2quote.html
--
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[Richard Heathfield]

CBFalconer said:

Richard Heathfield wrote:

>CBFalconer said:

>>Richard Heathfield wrote:
Walter Roberson said:
Sakula <jx*******@gmail.comwrote:
>
>/* includes */
>>
>#include<iostream.h>
>
That's a C++ program.

You may be right (although in fact you probably are not), but
the evidence cited above is insufficient to demonstrate this. C
implementations are free to ship headers by that name.

Well, later on he is doing such things as calling an undeclared
function 'new', and doing shifts into the undeclared variable
cout. You may want to reconsider your probabilities.

You may want to re-read my reply, and especially the first
sentence thereof.

Which is quoted in its entirety above. I see nothing new.

Your argument rests on "later on he is doing such things as...", whereas my
statement only referred to "the evidence cited above".

--
Richard Heathfield
"Usenet is a strange place" - dmr 29/7/1999
http://www.cpax.org.uk
email: rjh at above domain (but drop the www, obviously)

[Mark McIntyre]

On Mon, 11 Sep 2006 13:32:29 +0000, in comp.lang.c , Richard
Heathfield <in*****@invalid.invalidwrote:

>
Your argument rests on "later on he is doing such things as...", whereas my
statement only referred to "the evidence cited above".

Then its a nit you should not have picked, it just makes you look anal
about the wrong things.
--
Mark McIntyre

"Debugging is twice as hard as writing the code in the first place.
Therefore, if you write the code as cleverly as possible, you are,
by definition, not smart enough to debug it."
--Brian Kernighan

[Richard Heathfield]

Mark McIntyre said:

On Mon, 11 Sep 2006 13:32:29 +0000, in comp.lang.c , Richard
Heathfield <in*****@invalid.invalidwrote:

>>
Your argument rests on "later on he is doing such things as...", whereas
my statement only referred to "the evidence cited above".

Then its a nit you should not have picked

No such thing. :-)

--
Richard Heathfield
"Usenet is a strange place" - dmr 29/7/1999
http://www.cpax.org.uk
email: rjh at above domain (but drop the www, obviously)

[Mark McIntyre]

On Mon, 11 Sep 2006 21:41:10 +0000, in comp.lang.c , Richard
Heathfield <in*****@invalid.invalidwrote:

>Mark McIntyre said:

>On Mon, 11 Sep 2006 13:32:29 +0000, in comp.lang.c , Richard
Heathfield <in*****@invalid.invalidwrote:

>>>
Your argument rests on "later on he is doing such things as...", whereas
my statement only referred to "the evidence cited above".

Then its a nit you should not have picked

No such thing. :-)

I'll just cry "emerson" and pass on.
--
Mark McIntyre

"Debugging is twice as hard as writing the code in the first place.
Therefore, if you write the code as cleverly as possible, you are,
by definition, not smart enough to debug it."
--Brian Kernighan