Thread: Pointers

how do i get a pointer to "point" to a variable in another function?

this is what i have so far.

Code:

# include <conio.h>
# include <stdio.h>

void calculations(int,int);


void main (int sum,int diff)
{
   int num1,num2;
   int * pointer1;
   int * pointer2;


   printf ("Enter num1: ");
   scanf("%d",&num1);

   printf ("Enter num2: ");
   scanf("%d",&num2);

   calculations(num1,num2);
   pointer1 =&sum;
   pointer2 =&diff;


   printf ("The sum is : %d\n",pointer1);
   printf ("The sum is : %d\n",pointer2);


   getch();
}

void calculations (int num1,int num2)
{
    int sum,diff;

   sum = num1  + num2;
   diff = num1 - num2;

}

You don't. The variables sum and diff cease to exist when the function ends, and therefore you can't have pointers to them later (since there aren't any variables for them to point to). You can pass in pointers to a function, to have the function change the values those pointers point to; or you can have a function return a pointer (but not a pointer to a local variable!).

so instead i shud just make the variables pointers and i'll be able to use em and get the correct value anywhere?

ok, say i have a function that does the basic arithmetic + - / *.


how do i get to use the results in that function without using global variables?

Originally Posted by laserlight

You can have the function return a value, or you can pass a pointer to the function and store the result in the object that is pointed to.

i know how to return a value but could you show me how to "you can pass a pointer to the function and store the result in the object that is pointed to."?

Or you can return a value like

Code:

# include <conio.h>
# include <stdio.h>

calculations (int num1,int num2)
{
    int sum ,diff;
	char result;
	fputs("For sum press s and for diff press anything else: ",stdout);
	fflush(stdin);
	scanf("%c",&result);
	if(result=='s')
	return sum = num1  + num2;
else
return diff = num1 - num2;
}
int main (void)
{
   int num1,num2;
   int lol;
   fputs ("Enter num1: ",stdout);
   scanf("%d",&num1);
   printf ("Enter num2: ");
   scanf("%d",&num2);
   lol=calculations(num1,num2);
   printf ("The diff is : %d",lol);
getchar();
return 0;
}

Originally Posted by zacs7

@lolguy, Don't fflush(stdin) -- See the FAQ.

sometimes when i want a user to enter a string with " " (spaces) in it and i use gets, and sometimes it skips that input unless if i put a fflush infront of the gets.

why is that?

Originally Posted by Doc.

sometimes when i want a user to enter a string with " " (spaces) in it and i use gets, and sometimes it skips that input unless if i put a fflush infront of the gets.

why is that?

If you had previously used scanf to read in input, then there is still an enter-key in the input stream, which gets will read. The same FAQ has several methods for dealing.