Reverse string order using recursion

      This code implements a string reverse order function Reverse, and accepts the string input by the user in the main function, and then calls a> Reverse The function performs reverse order operation and finally outputs the reversed string.

//逆序字符串（递归）

void Resever(char *str)         //str这个指针指向数组首元素的位置
{
	char temp = *str;          //将str指向的元素赋给临时变量temp
	int len = strlen(str);     //求字符串长度
	*str = *(str + len - 1);   //将剩余字符串最后一个元素赋值给str指向的位置
	*(str + len - 1) = '\0';   //将剩余字符最后一个元素设置为\0
	if (strlen(str+1)>=2)      //判断剩余字符数是否大于等于2，若是，则继续递归
	{
		Resever(str + 1);
	}
	*(str + len - 1) = temp;   //将temp存起来的值赋给字符串末尾
}

int main()
{
	char arr[20] = "";
	printf("请输入一个字符串");
	scanf("%s", arr);
	Resever(arr);
	printf("逆序之后为: %s", arr);
	return 0;
}

The specific explanation is as follows:

1. void Reverse(char *str) Function:

   • char *str is a pointer to the first element of the character array, used to receive the string to be reversed.
   • char temp = *str; Save the first character pointed to by the pointer str into the temporary variable temp .
   • int len = strlen(str); Use the strlen function to get the length of the string.
   • *str = *(str + len - 1); Replaces the first character of the string with the last character of the string.
   • *(str + len - 1) = '\0'; Set the last character of the original string as the string terminator \0, which can truncate the original string.
   • if (strlen(str + 1) >= 2) Determine whether the remaining number of characters is greater than or equal to 2. If so, call the Reverse function recursively to perform reverse order operations on the remaining strings.
   • *(str + len - 1) = temp; Place the previously saved first character temp back to the end of the string.

2. int main() Function:

   • Create a character array arr to store the string entered by the user.
   • Use scanf("%s", arr); to accept a string entered by the user.
   • Call Reverse(arr); to perform reverse order operation on the input string.
   • Use printf("逆序之后为: %s", arr); to output the string in reverse order.

 Required knowledge points:

• Representation and operation of strings: Strings in C language are stored in the form of character arrays, ending with \0. Strings can be easily manipulated using character pointers.
• Pointers and pointer operations: The code uses pointers to operate array elements. For example, *str means getting the value pointed by the pointer, str + len - 1 means moving the pointer to the array. somewhere in.
• Recursion: The function uses recursive calling itself to implement the reverse order operation of the string.
• String input and output: Use scanf to input a string, and use printf to output a string.