21天学通C++ 所有实例

winbug

1.1 Hello World程序

#include <iostream>

int main()
{
    std::cout << "Hello World!" << std::endl;
    return 0;
}

/*
* 输出： Hello World!
* 生成
* Linux:
* g++ -o hello Hello.cpp
* Windows:
* Microsoft Visual Studio 
* Ctrl + F5
*/

winbug

3.1 使用变量存储数字及其相乘的结果。

#include <iostream>
using namespace std;

int main()
{
    int firstnum, secondnum;
    cout << "This program will help you multiply two numbers \n";
    cout << "Enter the first number: ";
    cin >> firstnum;
    cout << "Enter the second number: ";
    cin >> secondnum;
    cout << firstnum << " x " << secondnum << " = " << firstnum * secondnum << endl;
    return 0;
}
/*
*输出 51 x 24 = 1224
*/

winbug

3.2 使用变量存储数字机器相乘的结果函数版

#include <iostream>
using namespace std;

void MultiplyNumbers()
{
    cout << "Enter the first number: ";
    int firstnum =0, secondnum=0;
    cin >> firstnum;
    cout << "Enter the second number: ";
    cin >> secondnum;
    cout << firstnum << " x " << secondnum << " = " << firstnum * secondnum << endl;
}

int main()
{
    
    cout << "This program will help you multiply two numbers \n";
    MultiplyNumbers();
    
    return 0;
}

/*
* This program will help you multiply two numbers
* Enter the first number: 51
* Enter the second number: 24
* 51 x 24 = 1224
*/

winbug

创建int动态数组并动态的插入值

#include <iostream>
#include <vector> //动态数组
using namespace std;

int main()
{
	vector<int> dynArray(3); 
	dynArray[0] = 365;
	dynArray[1] = -421;
	dynArray[2] = 789;

	cout << "Number of integers in array: " << dynArray.size() << endl;
	cout << "Enter another element to insert " << endl;
	int newValue = 0;
	cin >> newValue;
	dynArray.push_back(newValue); //在数组后插入新值
	cout << "Number of integers in array: " << dynArray.size() << endl;
	cout << "Last element in array:";
	cout << dynArray[dynArray.size() - 1] << endl;
	return 0;
}

/*
* 输出
* Number of integers in array: 3
* Enter another element to insert
* -560
* Number of integers in array: 4
* Last element in array:-560
*/

winbug

演示如何对用户输入的整数执行算术运算

#include <iostream>
using namespace std;

int main()
{
    cout << "Enter two integers: " << endl;
    int num1 = 0, num2 = 0;
    cin >> num1;
    cin >> num2;

    cout << num1 << " + " << num2 << " = " << num1 + num2 << endl;
    cout << num1 << " - " << num2 << " = " << num1 - num2 << endl;
    cout << num1 << " x " << num2 << " = " << num1 * num2 << endl;
    cout << num1 << " / " << num2 << " = " << num1 / num2 << endl;
    cout << num1 << " % " << num2 << " = " << num1 % num2 << endl;
    return 0;
}

/*
* Enter two integers:
* 365
* 25
* 365 + 25 = 390
* 365 - 25 = 340
* 365 x 25 = 9125
* 365 / 25 = 14
* 365 % 25 = 15 
* 
*/```

winbug

使用按位右移运算符和左移运算符计算整数的1/4 1/2 2倍 4倍

#include <iostream>
using namespace std;

int main()
{
    cout << "Enter a number: ";
    int inputNum = 0;
    cin >> inputNum;

    int halfNum = inputNum >> 1;
    int quarterNum = inputNum >> 2;
    int doubleNum = inputNum << 1;
    int quadrupleNum = inputNum << 2;

    cout << "Quarter: " << quarterNum << endl;
    cout << "Half: " << halfNum << endl;
    cout << "Double: " << doubleNum << endl;
    cout << "Quadruple: " << quadrupleNum << endl;

    return 0;
}

/*
* 输出
* Enter a number: 16
* Quarter: 4
* Half: 8
* Double: 32
* Quadruple: 64
*/

winbug

6.1根据用户输入决定将两个正数相乘还是相加

#include <iostream>
using namespace std;

int main()
{
    cout << "Enter two integers: " << endl;
    int num1 = 0, num2 = 0;
    cin >> num1;
    cin >> num2;
    cout << "Enter 'm' to multiply, anything else to add: ";
    char ch;
    cin >> ch;
    if (ch == 'm')
    {
        cout << "Result is: " << num1 * num2 << endl;
    }
    else
    {
        cout << "Result is: " << num1 + num2 << endl;
    }
    return 0;
}

/*
* 输出
* Enter two integers: 
25
56
Enter 'm' to multiply, anything else to add:
s
Result is: 81
*/

winbug

6.2 将字符串复制到char数组之前，检查数组的容量

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

int main()
{
    cout << "Enter a line of text: " << endl;
    string userInput;
    getline(cin, userInput);

    char copyInput[20] = { '\0' };
    if (userInput.length() < 20)
    {
        strcpy_s(copyInput, userInput.c_str()); //strcpy_s 字符串复制 c_str()返回一个指向正规C字符串的指针常量
        cout << "copy Input contains: " << copyInput << endl;
    }
    else
    {
        cout << "Bounds excceeded: won't copy!" << endl;
    }
    return 0;
}


/*
* 输出
*Enter a line of text:
I am a chinese
copy Input contains: I am a chinese
*/

winbug

8.1 获取int 和 double的变量地址

#include <iostream>
using namespace std;

int main()
{
    int age = 30;
    const double Pi = 3.1416;

    cout << "Integer age is located at: 0x" << &age << endl;
    cout << "Double Pi is located at: 0x" << &Pi << endl;

    return 0;
}
/*
* 输出
Integer age is located at: 0x00D4F8E4
Double Pi is located at: 0x00D4F8D4
*/

8.2 声明并初始化指针

#include <iostream>
using namespace std;

int main()
{
    int age = 30;
    int* pointsToInt = &age;

    cout << "Integer age is located at: 0x" << hex << pointsToInt << endl;

    return 0;
}
/*
* 输出
Integer age is located at: 0x0116FC40
*/

8.3 给指针重新赋值，使其指向另一个变量

#include <iostream>
using namespace std;

int main()
{
    int age = 30;
    int* pointsToInt = &age;
    cout << "PointsToInt points to age now\n";
    cout << "PointsToInt = 0x" << hex << pointsToInt << endl;

    int dogsAge = 9;
    pointsToInt = &dogsAge;
    cout << "PointsToInt points to dogsAge now\n";
    cout << "PointsToInt = 0x" << hex << pointsToInt << endl;

    return 0;
}
/*
* 输出
PointsToInt points to age now
PointsToInt = 0x0074FECC
PointsToInt points to dogsAge now
PointsToInt = 0x0074FEB4
*/

使用解除引用运算符（*）来访问整数值

#include <iostream>
using namespace std;

int main()
{
    int age = 30;
    int dogsAge = 9;

    cout << "Integer age = " << age << endl;
    cout << "Integer dogsAge = " << dogsAge << endl;

    int* pointsToInt = &age;
    cout << "PointsToInt points to age\n";
    cout << "PointsToInt = 0x" << hex << pointsToInt << endl;
    cout << "*PointsToInt = " << dec << *pointsToInt << endl;

    pointsToInt = &dogsAge;
    cout << "PointsToInt points to dogsAge now\n";
    cout << "PointsToInt = 0x" << hex << pointsToInt << endl;
    cout << "*PointsToInt = " << dec << *pointsToInt << endl;

    return 0;
}
/*
* 输出
Integer age = 30
Integer dogsAge = 9
PointsToInt points to age
PointsToInt = 0x0027FAF0
*PointsToInt = 30
PointsToInt points to dogsAge now
PointsToInt = 0x0027FAE4
*PointsToInt = 9
*/

8.5使用指针和解除引用运算符操纵数据

#include <iostream>
using namespace std;

int main()
{
    int dogsAge = 30;
    cout << "Initialized dogsAge = " << dogsAge << endl;

    int* pointsToAnAge = &dogsAge;
    cout << "pointsToAnAge points to dosAge\n";
    
    cout << "Enter an age for your dog:";
    cin >> *pointsToAnAge;

    cout << "Input stored at  0x" << hex << pointsToAnAge << endl;
    cout << "Integer dogsAge = " << dec << dogsAge << endl;

    return 0;
}
/*
* 输出
Initialized dogsAge = 30
pointsToAnAge points to dosAge
Enter an age for your dog:10
Input stored at  0x00B3F7E0
Integer dogsAge = 10
*/

8.11数组变量是指向第一个元素的指针

#include <iostream>
using namespace std;

int main()
{
    int myNumbers[5];

    int* pointToNums = myNumbers;
    cout << "PointToNums = 0x" << hex << pointToNums << endl;
    cout << "&myNumbers = 0x" << hex << &myNumbers[0] << endl;

    return 0;
}
/*
* 输出
PointToNums = 0x001BFCDC
&myNumbers = 0x001BFCDC
*/

8.12 使用解除引用运算符（*）访问数组中的元素以及将数组运算符（[]）用于指针

#include <iostream>
using namespace std;

int main()
{
    const int ARRAY_LEN = 5;
    int myNumbers[ARRAY_LEN] = { 24, -1, 365, -999, 2011 };
    int* pointToNums = myNumbers;

    cout << "Display array using pointer syntax, operator*" << endl;
    for (int index = 0; index < ARRAY_LEN; ++index)
    {
        cout << "Element " << index << " = " << myNumbers[index] << endl;
    }

    cout << "Display array using ptr with array syntax, operator[] \n";
    for (int index = 0; index < ARRAY_LEN; ++index)
    {
        cout << "Element " << index << " = " << pointToNums[index] << endl;
    }


    return 0;
}
/*
* 输出
Display array using pointer syntax, operator*
Element 0 = 24
Element 1 = -1
Element 2 = 365
Element 3 = -999
Element 4 = 2011
Display array using ptr with array syntax, operator[]
Element 0 = 24
Element 1 = -1
Element 2 = 365
Element 3 = -999
Element 4 = 2011
*/

8.18 一个计算平方值并通过引用参数返回结果的函数

#include <iostream>
using namespace std;

void GetSquare(int& number)
{
    number *= number;
}

int main()
{
    cout << "Enter a number you wish to square: ";
    int number = 0;
    cin >> number;
    GetSquare(number);
    cout << "Square is: " << number << endl;

    return 0;
}
/*
* 输出
Enter a number you wish to square: -2
Square is: 4
*/

winbug

9.1 Human类

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

class Human
{
public:
    string name;
    int age;

    void IntroduceSelf()
    {
        cout << "I am " + name << " and am " << age << " years old" << endl;
    }
};

int main()
{
    Human firstMan;
    firstMan.name = "Adam";
    firstMan.age = 30;

    Human firstWoman;
    firstWoman.name = "Eve";
    firstWoman.age = 28;

    firstMan.IntroduceSelf();
    firstWoman.IntroduceSelf();

    return 0;
}

/*
* 输出：
I am Adam and am 30 years old
I am Eve and am 28 years old
*/

9.2 一个对外隐藏真实年龄并将自己说得更年轻的Human 类

#include <iostream>
using namespace std;

class Human
{
private:
    int age;

public:
    void setAge(int inputAge)
    {
        age = inputAge;
    }

    int getAge()
    {
        if (age > 30)
        {
            return (age - 2);
        }
        else
        {
            return age;
        }
    }
};

int main()
{
    Human firstMan;
    firstMan.setAge(35);

    Human firstWoman;
    firstWoman.setAge(28);

    cout << "Age of firstMan " << firstMan.getAge() << endl;
    cout << "Age of firstWoman " << firstWoman.getAge() << endl;

    return 0;
}

/*
* 输出：
Age of firstMan 33
Age of firstWoman 28
*/

9.3 使用构造函数初始化类成员变量

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

class Human
{
private:
    string name;
    int age;

public:
    //构造函数，初始化类的成员
    Human()
    {
        age = 1;
        cout << "Constructed an instance of class Human" << endl;
    }

    void setName(string humanName)
    {
        name = humanName;
    }

    void setAge(int inputAge)
    {
        age = inputAge;
    }

    void IntroduceSelf()
    {
        cout << "I am " + name << " and am " << age << " years old" << endl;
    }
};

int main()
{
    Human firstWoman;
    firstWoman.setName("Eve");
    firstWoman.setAge(28);

    firstWoman.IntroduceSelf();

    return 0;
}

/*
* 输出：
Constructed an instance of class Human
I am Eve and am 28 years old
*/

9.4 包含多个构造函数的Human 类

类可以添加同名带有参数的构造函数

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

class Human
{
private:
    string name;
    int age;

public:
    //构造函数，初始化类的成员
    Human()
    {
        age = 1;
        cout << "Default constructor: name and age not set" << endl;
    }

    Human(string humansName, int humansAge)
    {
        name = humansName;
        age = humansAge;
        cout << "Overloaded constructor creates ";
        cout << name << " of " << age << " years" << endl;
    }
};

int main()
{
    Human firstman;
    Human firstWoman("Eve", 28);

    return 0;
}

/*
* 输出：
Default constructor: name and age not set
Overloaded constructor creates Eve of 28 years
*/