void reverse(char* p, int len)
{
	char* left = p;
	char* right = p + len - 2;
	while (left < right)
	{
		char* temp = left;
		*left = *right;//当*left=*right后，*temp已经被改为f了
		*right = *temp;//你再*temp赋值给*right时，已经没用了
		left++;
		right--;
	}

}


int main()
{
	char arr[] = "abcdef";
	int len = sizeof(arr) / sizeof(char);
	printf("%d\n", len);
	reverse(arr, len);
	printf("%s\n", arr);



	return 0;
}

局部变量是存放在栈上的，栈又是从高到底存放所以先存i后存arr[]

打印菱形

#include<stdio.h>

int main()
{
	int line = 0;
	scanf("%d", &line);//7
	for (int i = 1; i <= line; i++)
	{
		for (int j = 0; j < line-i; j++)
		{
			printf(" ");
		}
		for (int j = 0; j < 2 * i - 1; j++)
		{
			printf("*");
		}
		printf("\n");
	}
	for (int i = 1; i < line; i++)
	{
		for (int j = 0; j < i; j++)
		{
			printf(" ");
		}
		for (int j = 0; j < 2 * (line - i) - 1; j++)
		{
			printf("*");
		}
		printf("\n");
	}



	return 0;
}

凶手是谁？

char killer = 0;
for (killer = 'A'; killer <= 'D'; killer++)
{
	if ((killer != 'A') + (killer == 'C') + (killer == 'D') + (killer != 'D') == 3)
	{
		printf("%c\n", killer);
	}
}