/* goodSwap.c - in class exercise solution

    - int swap via pointer args and passing addresses
    of actual parameters
*/

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

/* functions must either be declared (via prototype) or defined before use
   here we just define it first
*/

/*
   GETINTS: prompts for and returns 2 ints
   return value of 0 means both ints successfully gotten from kbd
   any other value indicates an error. return vals not to be used
*/
int getInts(int *a, int *b)
{
    #define EXPECTED_CONVERSIONS 2
    printf("Enter %d ints separated by whitespace: ", EXPECTED_CONVERSIONS);

    /* Note below we don't put '&' before a and b as they are addresses */

    return scanf("%d %d", a, b) - EXPECTED_CONVERSIONS;
}

/*
  SWAPINTS: uses addresses/pointers to exchange values of incoming arguments
*/
void swapInts(int *a, int *b)
{
    int temp = *a;
    *a = *b;
    *b = temp;
}

/*
  PRINT: argument values are copied in, no modification, no need to pass addresses
*/
void printInts(int a, int b)
{
    printf("1st arg= %d  2nd arg= %d\n", a, b);
}

/*........................M A I N    F U N C T I O N........................*/
int main(int argc, char *argv[])
{
    int x, y; /* compiler does not guarantee initialized to zero or anything else */

    if (getInts(&x, &y)) /* in C, any non-zero value is TRUE, only zero is FALSE */
    {
	fprintf(stderr,"Conversions failed. Program exiting.\n\n");
	exit(EXIT_FAILURE);
    }
    printf("\nBefore swap: ");
    printInts(x, y);
    swapInts(&x, &y);
    printf("\nAfter swap:  ");
    printInts(x, y);

    return EXIT_SUCCESS;
}