why dosen't this code about pointers work ?

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1.00/5 (3 votes)

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#include<iostream>

using namespace std;

int main()
{
    double *iii=123;
    cout << *(iii);
    cin.get();
    return 0;
}

this is a simple code using pointers, why dosen't it work
why dose the compiler thwor an aeeor saying "invalid conversion from int to int*"

Posted 2-Oct-13 2:59am

A.U.K

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joshrduncan2012 2-Oct-13 9:05am

Have you tried debugging the code to see where the problem is? What makes you think we will answer a question without any effort on your part first to see what the problem is?

A.U.K 5-Oct-13 8:45am

well, i did!
and the compiler says, " invalid conversion from int to int* ".
i din't understand that, i tried making so many adjustmentes, but it simply repeats the same error.

5 solutions

Solution 4

C#

#include<iostream>

using namespace std;

int main()
{
    double *iii=NULL;
    *iii = 11.13;
    cout<<*iii;
    cin.get();

    return 0;
}

pointer must be initialized with null at the time of declaration.
declared double pointer and initialized to const int.

after declaration now assign the double value into double pointer.

Posted 9-Mar-14 19:58pm

ranjithkumar81

Solution 5

C++

double *iii;

iii is a pointer of double. you can't assign value to it. you can assign only double variable address to it.
you can do it as follows,

C++

#include<iostream>
 
using namespace std;
 
int main()
{
    double val = 123.0;
    double * iii = &val;
    cout<<*iii;
    cin.get();
 
    return 0;
}

Posted 9-Mar-14 20:24pm

N.Banukobhan

Updated 9-Mar-14 20:26pm

v2

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OriginalGriff · Accepted Answer · 2013-10-02T03:09:00

Well... lets look at it this way.

double *iii

declares a variable called "iii" which is a pointer to a double. Which means that it contains the address of double values, hence the name "pointer" - it "Points" to the value.

Is a number which can be treated as a double.
So

C++

double *iii=123

Declare a pointer to a double and tries to put a double value into it. Not the address of a double, but the value itself.

If you think of a car key as the "pointer" to a car then you are trying to drive the key instead of the car!

I think you need to go back to your lecture notes and read through this stuff again, but the first line could be made to work if you did this:

C++

double vd = 123;
double *iii=&vd;

Because in this case you are putting the address of a double into the pointer. Note that you can't take the address of a constant:

C++

double *iii=&123;

because then you could try to modify constants and the PC Pixies don't like you trying to do that...

CPallini · Accepted Answer · 2013-10-02T03:29:00

Quote:
double *iii=123;

The above line is wrong (a pointer must point. You need something like:

C

double d = 123.0;
double *iii; // pointer variable declaration
iii = &d; // pointer variable initialisation

You may short-cut the last two lines into:

C

double *iii = &d; // pointer variable declaration and initialisation

Richard MacCutchan · Accepted Answer · 2013-10-02T03:11:00

Solution 2

You need to separate the declaration and initialization, like;

C++

double *iii;
*iii = 123;

In your original code you are trying to set the pointer iii to the value 123. And since iii is a pointer it needs to be set to the address of a value, rather than the value itself. And you cannot do this with a direct constant so you need to split the expression as above.

Posted 2-Oct-13 3:11am

Richard MacCutchan

Comments

CPallini 2-Oct-13 9:32am

Are you really suggesting the OP to de-reference a uninitialised pointer? :-)

Richard MacCutchan 2-Oct-13 9:38am

Damn, what's happened to my brain?

[no name] 2-Oct-13 9:47am

Not just yours, others fell for the (deliberate?) mistake.

Richard MacCutchan 2-Oct-13 11:54am

Indeed, someone even gave me a 5.