[C++] 用Xcode来写C++程序[3] Constants

用Xcode来写C++程序[3] Constants

以下是一些基本数据的含义:

75         // int
75u        // unsigned int
75l        // long
75ul       // unsigned long 
75lu       // unsigned long 

3.14159    // 3.14159
6.02e23    // 6.02 x 10^23
1.6e-19    // 1.6 x 10^-19
3.0        // 3.0  

3.14159L   // long double
6.02e23f   // float  

‘z‘        // 单个字符

"How do you do?"  // 字符串

一些符号的含义:

bool类型以及指针

bool foo = true;
bool bar = false;
int* p = nullptr;

const变量

#include <iostream>
using namespace std;

const double pi = 3.14159;
const char newline = ‘\n‘;

int main ()
{
  double r=5.0;               // radius
  double circle;

  circle = 2 * pi * r;
  cout << circle;
  cout << newline;

宏定义:

#include <iostream>
using namespace std;

#define PI 3.14159
#define NEWLINE ‘\n‘

int main ()
{
  double r=5.0;               // radius
  double circle;

  circle = 2 * PI * r;
  cout << circle;
  cout << NEWLINE;

}