Help understanding conditional operator
Code:
/* Inputs a list of strings from the keyboard, sorts them */
/* in ascending or descending order, then displays them */
#include <stdio.h>
#include <string.h>
#include <process.h>
#include <malloc.h>
#define MAXLINES 25
int get_lines(char *lines[]);
void sort(char *p[], int n, int sort_type);
void print_strings(char *p[], int n);
int alpha(char *p1, char *p2);
int reverse(char *p1, char *p2);
char *lines[MAXLINES];
void main(void)
{
int number_of_lines, sort_type;
/* Read in the lines from keyboard */
number_of_lines = get_lines(lines);
if (number_of_lines < 0)
{
puts("Malloc error");
exit(-1);
}
puts("Enter 0 for reverse order sort, 1 for alphabetical:");
scanf("%d", &sort_type);
sort(lines, number_of_lines, sort_type);
print_strings(lines, number_of_lines);
}
int get_lines(char *lines[])
{
int n = 0;
char buffer[80]; /* temp storage for each line */
puts("Enter on line at a time; enter blank when done");
while (n < MAXLINES && gets(buffer) != 0 && buffer[0] != '\0')
{
if ((lines[n] = (char *)malloc(strlen(buffer) + 1)) == NULL)
return -1;
strcpy(lines[n++], buffer); /* copy buffer to lines at [n] and increment n */
}
return n; /* return number of lines entered */
}
void sort(char *p[], int n, int sort_type)
{
int a, b;
char *x;
/* Pointer to function */
int (*compare)(char *s1, char *s2);
/* Initialize the pointer to point at the proper comparison */
/* function depending on the argument sort_type */
compare = (sort_type) ? reverse : alpha;
for (a = 1; a < n; a++)
{
for (b = 0; b < n-1; b++)
{
if (compare(p[b], p[b+1]) > 0)
{
x = p[b];
p[b] = p[b+1];
p[b+1] = x;
}
}
}
}
void print_strings(char *p[], int n)
{
int count;
for (count = 0; count < n; count++)
printf("\n%s ", p[count]);
}
int alpha(char *p1, char *p2)
/* Alphabetical comparison */
{
return(strcmp(p2, p1));
}
int reverse(char *p1, char *p2)
/* Reverse alphabetical comparison */
{
return(strcmp(p1, p2));
}
I'm having a little difficulty understanding the usage of the conditional operator (in blue). The user is supposed to enter 0 for a reverse sort and 1 for an alphabetical sort. If I understand the conditional op, if sort_type is true (i.e. non-zero) then the statement evaluates to reverse, otherwise it evaluates to alpha. But, the value to be entered for reverse is zero - so wouldn't that result in a false, and then set compare to alpha? I'm confused...