程序代码：

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


void main ( )
{
    void swap ( char *p1,char *p2, char *p3);
    char *p1, *p2, *p3;
    int i;
    char str[3][20];
    for ( i = 0; i < 3; i++ )
        gets ( str[i] );
    p1 = str[0];
    p2 = str[1];
    p3 = str[2];
    swap ( p1, p2, p3 );
        printf ( "%s%s%s", *p1, *p2, *p3 );
        system ( "pause" );
}

void swp ( char *p1, char *p2, char *p3 )
{
    if ( strcmp ( p1,p2 ) > 0 )
        strcpy ( p1, p2 );
    if ( strcmp ( p1, p3 ) > 0 )
        strcpy ( p1, p3 );
    if ( strcmp ( p2, p3 ) > 0 )
        strcpy ( p2, p3 );
    return ;
}