c++学习笔记04--关键字

1. sizeof

    作用：利用sizeof可以统计数据类型所占内存大小。

    语法：sizeof(数据类型/变量)。

    示例：

#include <iostream>
using namespace std;
 
 
int main() {
 
 
	int a = 10;
	short b = 10;
	long c = 10;
	long long d = 10;
	cout << "sizeof a=" << sizeof(a) << endl;
	cout << "sizeof b=" << sizeof(b) << endl;
	cout << "sizeof c=" << sizeof(c) << endl;
	cout << "sizeof d=" << sizeof(d) << endl;
	system("pause");
	return 0;
}

2. cin

    作用：用于从键盘获取数据。

    语法：cin >> 变量

#include <iostream>
#include <string>
using namespace std;
 
int main() {
 
	//整形
	int a = 0;
	cout << "请给整形a赋值" << endl;
	cin >> a;
	cout << "a = " << a << endl;
	//浮点型
	float b = 3.14F;
	cout << "请给浮点型b赋值" << endl;
	cin >> b;
	cout << "b = " << b << endl;
 
	//字符型
	char c = 'a';
	cout << "请给字符型c赋值" << endl;
	cin >> c;
	cout << "c = " << c << endl;
	//字符串型
	string d = "hello";
	cout << "请给字符串型d赋值" << endl;
	cin >> d;
	cout << "d = " << d << endl;
 
	//布尔型
 
	bool e = true;
	cout << "请给布尔型e赋值" << endl;
	cin >> e;//bool只要非0都为真
	cout << "e = " << e << endl;
 
	return 0;
}