big c++ 读书笔记

第4章 基本控制流

  零警告编译

  int pennies = static_cast<int>(100 * (amount_due - amount_paid));

 输入确定

 

#include<iostream>
#include<string>
#include<cmath>
using namespace std;
int main()
{
 double area;
 cout<< "Please enter the area of a square:";
 cin>>area;

 if(cin.fail())
 {
  cout<<"error:bad input\n";
  return 1;
 }

 if( area < 0)
 {
  cout<<"error : negaive area\n";
  return 1;
 }
}

 函数注释风格

  /**

   计算

  @param  x

  @param y

  @return

 **/

 

 

#include<iostream>
#include<string>
#include<cmath>
using namespace std;

/**
 测试两个浮点数是否相近
 @param x
 @param y
 @return true 若近识相等则为真
 **/

bool approx_equal(double x,double y)
{
 const double EPSION = 1E-14;
 if(x==0) return fabs(y) <= EPSION;
 if(y==0) return fabs(x) <= EPSION;
 return fabs(x-y) / max(fabs(x),fabs(y)) <= EPSION;
}
int main()
{
  double x;
  cout<<"Enter a number;";
  cin >>x;

  double y;
  cout<<"Enter another number;";
  cin>>y;

  if(approx_equal(x,y))
   cout<<"the numbers are approximately equal.\n";
  else
   cout<<" the numbers are different.\n";
  return 0;
}

 

 第九章

 

  1. C++中 实现数据项序列有更好的办法： 向量结构。

  2.vector<double> salaries;

  salaries[0] = 32000;

 若定义向量时不带长度参数，它将是空的并不能保持元素。

  3.