Solution for Exercise 08_08-daysweek.c

08_08-daysweek.c

#include <stdio.h>

void printall(char **w)
{
	char *temp;		/* pointer address storage */

	/* swap elements 1 and 5 */
	temp = *(w+1);
	*(w+1) = *(w+5);
	*(w+5) = temp;

	while(*w)
		puts(*w++);
}

int main()
{
	char *weekdays[] = {
		"Monday", "Tuesday", "Wednesday",
		"Thursday", "Friday", "Saturday",
		"Sunday", NULL
	};

	printall(weekdays);
	
	return 0;
}

Output

Monday
Saturday
Wednesday
Thursday
Friday
Tuesday
Sunday

Notes

* In the output you see that the strings Saturday and Tuesday are swapped.

* The printall() function echoes what's presented in the book. The argument is **w, which represents an array of pointers (strings).

* Character pointer temp is used for the swap. It's a character pointer in that it holds a string's address.

* The first and fifth pointers are swapped. These are at offset 1 and 5; 1 is the second element and 5 is the sixth.

* The expression *(w+1) represents the second element (Tuesday). It's string's address, which is saved in the temp pointer variable.

* The expression *(w+5) represents the fifth element (Saturday).

* Beyond the weird pointer notation, the swap takes place like any other variable swap in C. Remember that it's the addresses that are swapped; the string's contents are unaffected.

Exercise 08_13-addnodes.c →