Thread: Question about pointers

today i was trying some code in pointers whish really amaze me for incrementing but some variable i get weird results

Code:

#include <stdio.h>
int increment_it(int *num)
{
    int result;
    (*num)++;//this works
    *num=*num+1;//works
#ifdef USE_NON_WORKING
    *num++;//this doesnt
#endif
    return result;
}
int main(void)
{
    int x=0;
    increment_it(&x);
    printf("%d",x);
    getchar();
    return 0;
}

first i thought *num++; would just increment the address itself but it doesnt even increment anything so any idea what it doess coz this is really weird.

yah i know i made before that return result=*num; i just forgot to put it. but it

Code:

#include <stdio.h>
int increment_it(int *num)
{
    int result;
    (*num)++;//this works
    *num=*num+1;//works
#ifdef USE_NON_WORKING
    *num++;//this doesnt
#endif
    return result=*num;
}
int main(void)
{
    int x=0;
    increment_it(&x);
    printf("%d",x);
    getchar();
    return 0;
}

but isnt *num++ same as *num=*num+1; ?

Originally Posted by Snafuist

...and num is a local variable, so you won't notice any change in main().

*num++ increments num, not *num. Have a look at the operator precedence rules.

Greets,
Philip

num is a prameter in the function its not a local variable

yah i forgot x=increment_it(&x);

Code:

#include <stdio.h>
int increment_it(int *num)
{
    int result;
    (*num)++;//this will increment it to 1
    *num=*num+1;//this will increment it to 1
#ifdef USE_NON_WORKING
    *num++;//this wont increment it to 1
#endif
    return result=*num;
}
int main(void)
{
    int x=0;
    x=increment_it(&x);
    printf("%d",x);//result 2 coz i increment it twice
    getchar();
    return 0;
}

but why does *num++; deference is since i alrdy did in my function x=increment_it(&x); ?

oh i get it now also yah your right i didnt even need to return anything since its alrdy incremented it

I am finding little hard to comprehend things

Hope i am not hijacking the thread.

But in the following case:

Code:

int main()
{
   int i[] = {3, 5}; 
   int *p = i; 
   int j = --*p++; 
   
   printf("j = %d, p= %d\n\n", j,*p);
   //system("pause");
   return 0;
}

Things look little different

j = 2 and *p = 5

They say that Postfix (++ and --)has an associativity of left to right ,
but at the same time we can see a Prefix associated above, having an associativity of right to left.

Can explain how to comprehend the above line of code. how does the compiler preceive the above statement.

Thanks to all in advance

can someone explain