Question

我无法掌握C中指针的概念。从我收集的内容中，指针指向另一个变量的地址，然后可以对其进行操作。有些人可以解释如何将指针应用于字符串数组，特别是字符串中的每个字符，以便比较字符的排序和移位。我能够完成的这项任务的唯一部分是display_chunks函数。提前感谢您的帮助。

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

#pragma warning(disable: 4996)


#define CHUNK_LENGTH (20+1)  //each chunk has twenty characters, we add 1 so
                       //there is space for the null terminator.
#define NUMBER_OF_CHUNKS 4 //the message is spread across 4 chunks.
#define DECRYPTION_SHIFT 5 //this is the ASCII table shift used for decryption.


void sort_chunks();
void decrypt_chunks();
void display_chunks();

char chunks[NUMBER_OF_CHUNKS][CHUNK_LENGTH];

int main()
{
   //copy message into memory.
   strcpy(chunks[0], "2i1%fsi%fs%jstwrtzx%");
   strcpy(chunks[1], "1'H%nx%vznwp~1%kqf|j");
   strcpy(chunks[2], "4R3%Wnyhmnj%%%%%%%%%");
   strcpy(chunks[3], "3xzhhjxx3'%2%Ijssnx%");

//reorder chunks in message by sorting them based on the first digital
//they contain. looking above, one can see they are currently in the order
//2, 1, 4, 3 but should be ordered 1, 2, 3, 4.
sort_chunks();

//shift the characters in the message to produce the original characters.
decrypt_chunks();

//display the decrypted message.
display_chunks();

getc(stdin);
return 0; 
}

    //given two strings, swaps their contents in memory.
    void swap_strings(char* x, char* y)
{
//create a temporary holding place for the data so we don't lose it.
char temp[CHUNK_LENGTH];

strcpy(temp, x);
strcpy(x, y);
strcpy(y, temp);
}

//sorts the strings the global chunks variable by the first character they contain.
void sort_chunks()
{
   //TODO: Implement sort_chunks(). Using your favorite sorting algorithm (we
   //      suggest selection sort), sort the array containing the message chunks.
   //      Sort based on the first character in the chunk - it will always be a
   //      number. We provide a swap_strings function that you may use. Example
       //     usage: swap_strings(chunks[0], chunks[1]) will swap the contents of
   //      the first and second string. [20 points]

}

//for each string in the global chunks variable, shifts the characters in it by
//DECRYPTION_SHIFT.
void decrypt_chunks()  
{
//TODO: Implement decrypt_chunks(). Loop over each string in the array
//      and shift the characters in it by subtracting DECRYPTION_SHIFT value
//  from them. Use pointer arithmetic to access individual characters but
//  array access to the strings. Remember that C-style strings have a null
//  terminator at the end. Do not apply the shift to the terminator.
//  (Hint: to avoid doing double pointer arithmatic, save a char*   pointer
//  to the active chunk[?] in the outer loop but before the inner loop.
//  Then the inner loop is only concerned with a single array of
//  characters rather than an array of strings.) [10 points]
}


//displays the strings in the global chunks variable
void display_chunks()
{
int i;
//TODO: Implement display_chunks(). Loop over each string in the array of
//      message chunks (strings) and print it. Do not print the first
//      character in each string since it is only used to store the order of
//      the chunks. (Hint: use pointer arithmetic to skip a character.) [5 points]
for ( i = 0; i < 4; i++)
    printf(" %s\n",chunks[i]);

Answer 1

你的教练正在寻找的是洞察力，而不是排序字符串本身（这涉及移动大量数据），你可以对字符串的指针数组进行排序（更少的工作）。

使用C中的指针对字符串数组进行排序

1 个答案: