3.19study

#include 
 
/*
int Add(int x, int y)
{
  int z = 0;
  z = x + y;
  return z;
}
int main()
{
  int a = 10;//先压栈的后使用
  int b = 20;//后压栈的先使用   ----类似子弹夹
  int ret = 0;
  ret = Add(a, b);//传参先传b后传a

  return 0;
}
*/

/*
int main()
{
  int a = 20;
  //00000000000000000000000000001010--原码
  //00000000000000000000000000001010--反码
  //00000000000000000000000000001010--补码
  //0x00000014--HEX
  int b = -10;
  //10000000000000000000000000001010--原码
  //11111111111111111111111111110101--反码
  //11111111111111111111111111110110--补码
  //0xFFFFFF6--HEX
  return 0;
}
*/

/*
int main()
{
  //1 - 1;
  int a = 0x11223344; //先F10,调试-->窗口-->内存监视
  //1+(-1)
  //若用原码计算则=-2
  //采用补码计算
  //00000000000000000000000000000001 --正数原反补相同
  //11111111111111111111111111111111 -- -1的补码
  //00000000000000000000000000000000
  return 0;
}
*/

/*
int main()
{//设计一个程序判断当前字节序
  int a = 1;
  char* p = (char *)&a;
  if (*p == 1)
  {
    printf("小端n");
   }
  else
  {
    printf("大端n");
  }
  return 0;
}
*/

/*
int check_sys()
{
  int a = 1;
  char*p = (char*)&a;
  //返回1，小端
  //返回0，大端
  return *p;
}

int main()
{//设计一个程序判断当前字节序
  int ret=check_sys();
  if (ret == 1)
  {
    printf("小端n");
  }
  else
  {
    printf("大端n");
  }
  return 0;
}
*/

/*
int main()
{
  int a = 0x11223344;
//  int *p = &a;//指针类型决定了访问几个字节，int 访问四个字节
//  *p = 0;
  char* p = &a;//char访问1个字节
  *p = 0;

  return 0;
}
*/

/*
int main()
{
  char a = -1;
  //内存中存储的补码：11111111111111111111111111111111
  //只能存8个比特位即11111111-->整形提升-->11111111111111111111111111111111
  signed char b = -1;
  //11111111-->整形提升-->11111111111111111111111111111111
  unsigned char c = -1;//无符号数-->符号位为0
  //11111111-->整形提升-->00000000000000000000000011111111
  printf("a=%d b=%d c=%d",a,b,c);//-1 -1 255
  //
  return 0;
}
*/

/*
int main()
{
  char a = -128;
  char b = 128;//127+1
  //10000000000000000000000010000000 -->原码
  //11111111111111111111111110000000 -->补码
  //存放于a中-->10000000
  //整形提升后11111111111111111111111110000000
  printf("%un",a);//%u -->打印十进制的无符号数字
  printf("%un",b);
   //由于%u认定存放于内存的为无符号数，故原反补相同，直接打印
  //%d -->打印十进制有符号数
  return 0;
}
*/

/*
int main()
{
  int i = -20;
  //10000000000000000000000000010100--原码
  //11111111111111111111111111101011--反码
  //11111111111111111111111111101100--补码
  unsigned int j = 10;
  //00000000000000000000000000001010--原反补
  printf("%dn",i+j);//-10
  //11111111111111111111111111110110--结果(补码)
  //11111111111111111111111111110101--反码
  //10000000000000000000000000001010--原码(打印出的结果)
  return 0;
}
*/

/*
int main()
{
  unsigned int i;//i为无符号数，最小为0，故一直满足for循环
  for (i = 9; i >= 0; i--)
  {
    printf("%un", i);//死循环
  }


  return 0;
}
*/

/*
int main()
{
  //char表示范围-128~127
  char a[1000];//0~999
  int i;
  for (i = 0; i 
  {
    a[i] = -1 - i;// -1,-2,-3,...-127,-128,127,126,125,....3,2,1,0-->为截止位，故有128+127位=255
  }         //-128时再-1为-127即1000000000000000000   -1-->011111111111111111111
  printf("%d",strlen(a));//255  的ASCII码为0

  return 0;
}
*/


/*
unsigned char i = 0;//0~255
int main()
{
  for (i = 0; i 
  {
    printf("hello worldn");//死循环
  }

  return 0;
}
*/

/*
int main()
{
  double d = 1E10;
  printf("%lfn",d);

  return 0;
}
*/

int main()
{
  int n = 9;
  float* pFloat = (float*)&n;
  printf("n的值为：%dn",n);//9
  printf("*pFloat的值为：%fn",*pFloat);//0.000000

  *pFloat = 9.0;
  printf("num的值为：%dn", n);//1091567616
  printf("*pFloat的值为：%fn", *pFloat);//9.000000

  return 0;
}