ptrsort.c

里面包含很多c语言的源码

/* Inputs a list of strings from the keyboard, sorts them */
/* in ascending or descending order, and then displays them */
/* on the screen. */
#include <stdlib.h>
#include <stdio.h>
#include <string.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];

int main( void )
{
   int number_of_lines, sort_type;

   /* Read in the lines from the keyboard. */

   number_of_lines = get_lines(lines);

   if ( number_of_lines < 0 )
   {
       puts("Memory allocation 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);
   return 0;
}

int get_lines(char *lines[])
{
    int n = 0;
    char buffer[80];  /* Temporary storage for each line. */

    puts("Enter one line at time; enter a 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 );
    }
    return n;

} /* End of get_lines() */

void sort(char *p[], int n, int sort_type)
{
    int a, b;
    char *x;

    /* The pointer to function.  */

    int (*compare)(char *s1, char *s2);

    /* Initialize the pointer to point to 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;
            }
        }
    }
}  /* end of sort() */

void print_strings(char *p[], int n)
{
    int count;

    for (count = 0; count < n; count++)
        printf("%s\n", 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));
}