Thread: Passing Variables to Functions -- Invalid in C99

This latest C book by Greg Perry needs updating, especially in the last chapters. Forgive my noob question but I'm trying to make this program work:

Code:

#include <stdio.h>
#include <stdlib.h>


int main() {
	
  int i; 


  printf("Please enter an integer...\n"); 
  scanf(" %d", &i); 


  // Now call the half function, passing the value of i
  half(i)


  // Shows that the function did not alter i's value
  printf("In main(), i is still %d.\n", i); 


return(0); 


}


/*******************/
/* Sometimes putting dividers like the one above is a nice break between your different functions. */


  half(int i) { // Receives the value of i


  i = 1 / 2; 
  printf("Your value halved is %d.\n", i); 
  return; // Returns to main


}

What's the correct way to make the 'half' function work?

Thank you, algorism!

Originally Posted by GReaper

Is that a new book? It seems like pre-standard 80s C to me...

If it's the 3rd edition of "C Programming Absolute Beginner's Guide" from 2013, then it's supposed to be "updated for C11". The 2nd edition is from 1994, so it should still be C89. However, this free sample chapter from the 3rd edition still doesn't put "int" before main.
http://ptgmedia.pearsoncmg.com/image...0789751984.pdf
(see page 14)

Code:

/* assign value of (i / 2) to i's memory */
void half(int *i)
{
	*i = (*i / 2);
}


int main()
{
	int number = 400;
	half( &number );
	printf("number=%d\n", number);
	return 0;
}

to change its value you have to pass its address or assign the return value of the function to your variable.

@wrvc

to change its value you have to pass its address or assign the return value of the function to your variable.

Yes, this is true, but please read the code the OP posted:

// Shows that the function did not alter i's value

The purpose of the code posted was to illustrate that the variable, 'i' in the two functions are different, and altering the one in half() has no affect on the one in main(). The chapter on pointers would then cover passing the address of 'i' to alter the one in main().