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//定义一个字符型数组,用关键字sizeof求长度

#include <iostream>

int main()
{

	char a[1000];
	int i;
	printf("hello world\n");

	for (i = 0; i < 1000; i++)
	{
		a[i] = -1 - i;
		//printf("%d\n",a[i]);

	}
	printf("the size of i %d\n",sizeof(i));
	printf("the size of i %d\n", sizeof(char));
	printf("the size of i %d\n", sizeof(a));
	printf("%d\n", strlen(a));
	
	return 0;
}
//结果
C:\Users\kanxue\Desktop\VS\ConsoleApplication1\Debug>ConsoleApplication1.exe
hello world
the size of i 4
the size of i 1
the size of i 1000
255

//定义一个singned int变量和unsigned int相加得到结果

#include <iostream>

int main()
{
	int i = -20;
	unsigned int j = 10;

	printf("the i+j valude is %d\n", i + j);

	return 0;

}

//结果很快就能得出结果,我们这里主要是分析原因
C:\Users\kanxue\Desktop\VS\ConsoleApplication1\Debug>ConsoleApplication1.exe
the i+j valude is -10

分析:编译器缺省默认情况下数据为signed类型,在计算机系统中,数值一律用补码来表示,正数的补码和原码一致,负数的补码:符号为为1,其余位位该数绝对值的源码按位取反,然后整个数加1;

-20用正常二进制表示为: 1001 0100 ,其补码为:1110 1100

10二进制表示为:0000 1010

两者相加:1110 1100 + 0000 1010 = 1111 0110 其补码为:1000 1010 -> -10

#include <stdio.h>
int main()
{
	int a[5] = {1,2,3,4,5};
	int *ptr = (int *)( &a + 1);
 
	printf("%d, %d, \n", *(a+1), *(ptr-1) );
	return 0;
}

//结果
C:\Users\curtis\Desktop\VS\static\Debug>static.exe
2, 5,

数组名 a 的特殊之处:

&a : 代指 数组的整体 的地址,这里的 a是数组整体

a+1: 代指 数组的第一个成员,这里的 a是数组首地址

#include <iostream>

#define SQR(x) printf("The square of "#x" is %d.\n", ((x)*(x)));

int main()
{
	signed i;
	int *p;
	printf("sizeof *p is %d\n", sizeof(p));

	SQR(3);

	for (i = 9; i >= 0; i--)
	{
		printf("%u\n", i);
	}

	return 0;
}

//
C:\Users\kanxue\Desktop\VS\ConsoleApplication1\Debug>ConsoleApplication1.exe
sizeof *p is 4
The square of 3 is 9.
9
8
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5
4
3
2
1
0



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