Two methods of printing strings in reverse order in C language

Non recursive
Non recursive thinking is more clever , Here's the picture ：

Let's exchange the first one with the penultimate one , Exchange the second and penultimate , Exchange the third and the penultimate …

You may ask ：“ What if the number of characters in my string is odd ？”
The answer is , The character in the middle is exchanged with himself , It doesn't matter , He is still in his position .

void reverse_string(char* str)
{
    
	int len = strlen(str);
	char* left=str;
	char* right = str + len - 1;
	while (left < right)
	{
    
		char tmp = *left;
		*left = *right;
		*right = tmp;
		left++;
		right--;
	}
}
int main()
{
    
	char arr[20] = {
     0 };
	printf(" Please enter the string you want in reverse order ：");
	scanf("%s", arr);
	reverse_string(arr);
	printf("%s", arr);
	return 0;
}

recursive

The idea of recursion is very simple , It's going down layer by layer “ Deliver ”, Until the string becomes only one character , Then print that character
Then it goes up layer by layer “ return ”, Print the character locked by the pointer

void reverse_string(char* str)
{
    
	if (*str != '\0')
	{
    
		reverse_string(str + 1);
	}
	printf("%c", *str);
}
int main()
{
    
	char arr[20] = {
     0 };
	printf(" Please enter the string you want in reverse order ：");
	scanf("%s", arr);
	reverse_string(arr);
	return 0;
}