pass by address program

I need help in my program

Code:

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#include <stdio.h>
void pass (int *x);
 
 
int main(void)
{
    int a = 12;
    printf("address of a is : %p \n", &a);
    printf("value of a is : %d\n", a); 
   
    pass (&a);
   
    printf("after calling address of a is : %p\n", &a);
        printf("after calling value of a is : %d\n", a);   
   
    return 0;
}
 
 
void pass (int *x)
{
   
  *x = 10;
   
  printf("address of x is : %p\n", x);
  printf("value of x is : %d\n", *x); 
   
}

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Program result
address of a is : 0061FF2C
value of a is : 12
address of x is : 0061FF2C
value of x is : 10
after calling address of a is : 0061FF2C
after calling value of a is : 10

The address has not been changed. In this code:

Code:

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    printf("address of a is : %p \n", a);
 // ...



    printf("after calling address of a is : %p\n", a);

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Is 'a' an address? No, &a is though. I think now is a good time to turn on warnings for your compiler.

Quote:

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Originally Posted by Hodor

The address has not been changed. In this code:

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you posted hint while I was editing post.

pass by value

Code:

---

#include <stdio.h>
void pass (int x);
 
 
int main(void)
{
    int a = 12;
    printf("address of a is : %p \n", a);
    printf("value of a is : %d\n", a); 
   
    pass (a);
   
    printf("after calling address of a is : %p\n", a);
        printf("after calling value of a is : %d\n", a);   
   
    return 0;
}
 
 
void pass (int x)
{
   
  x = 10;
   
  printf("address of x is : %p\n", &x);
  printf("value of x is : %d\n", x); 
   
}

---

address of a is : 0000000C
value of a is : 12
address of x is : 0061FF10
value of x is : 10
after calling address of a is : 0000000C
after calling value of a is : 12

if I compare both program pass by address code is more meaningful because it save the memory of hardware. correct me if I am wrong

ok, in main() 'a' is an integer, not a pointer to an integer so change these lines (line 8 and 13)

Code:

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printf("address of a is : %p \n", a); /* line 8 */
printf("after calling address of a is : %p\n", a); /* line 13 */

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to

Code:

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printf("address of a is : %p \n", &a);
printf("after calling address of a is : %p\n", &a);

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Because you want a pointer to 'a', not 'a' itself (which is why I added the & before the a)

Ok, now that's fixed, what compiler are you using because there is no modern compiler that I am aware of that will not warn that you're passing the wrong datatype (an int and not a pointer to int, in this case)?

Quote:

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Originally Posted by vajra11

if I compare both program pass by address code is more meaningful because it save the memory of hardware. correct me if I am wrong

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No, that's wrong. You're passing the address because you want to modify the value of 'a' and for that modified value be reflected in the calling function (in this case, main()).

I just noticed that your new program is wrong. The new version will not modify the value of x (which is a copy of a from main). C only has pass by value, so 'x' (in pass()) is a copy of 'a' (from main()) so the value of 'a' in main will remain unchanged because pass() made a copy and worked on the copy. If you want to change the value of 'a' in main then do this:

Code:

---

#include <stdio.h>
void pass (int x);
 
 
int main(void)
{
    int a = 12;
    printf("address of a is : %p \n", &a);

    printf("value of a is : %d\n", a); 

     

    pass (&a);

     

    printf("after calling address of a is : %p\n", &a);

    printf("after calling value of a is : %d\n", a);   

     
    return 0;
}
 
 
void pass (int *x)

{
   
  *x = 10;

   
  printf("address of x is : %p\n", x);

  printf("value of x is : %d\n", *x); 

   
}

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Quote:

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Originally Posted by Hodor

I just noticed that your new program is wrong. The new version will not modify the value of x (which is a copy of a from main). C only has pass by value, so 'x' (in pass()) is a copy of 'a' (from main()) so the value of 'a' in main will remain unchanged because pass() made a copy and worked on the copy. If you want to change the value of 'a' in main then do this:

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Thank you Hodor for clear explanation