实验二选择程序设计（C++）

约定不等于承诺〃 2022-04-24 01:36 227阅读 0赞

## **实验二   选择程序设计（C++）** ##

### **一、实验目的** ###

1、学习与掌握逻辑运算与逻辑表达式。

2、熟练掌握if、switch语句的语法结构与执行过程。

3、掌握选择程序的设计方法

### **二、实验内容** ###

1、输入一个字符，如果为小写，转换为大写输出，否则，输出其后继字符的ASCII码值。

2、输入x计算表达式的值：

![20190411155255817.png][]

3、输入三角形的三条边，求周长，并判断该三角形是否为等腰三角形（提示：要三边是否可以构成三角形）。

4、完成计算器程序，实现（+ - \* / %）运算。考虑除数为0与运算符非法的情况。

### **三、实验步骤、算法与结果分析** ###

**1、字符的转换与输出**

(1)算法：

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM5NTY0NTU1_size_16_color_FFFFFF_t_70][]

(2)程序：

#include <iostream>
    using namespace std;
    int main()
    {
    	char a[20];
    	int i=0;
    	cout<<"please input a character:\n";
    	cin>>a;
    	if(a[i]>='a'&&a[i]<='z')
    	{
    	    a[i] -=32;
    		cout<<a[i]<<endl;
    	}
    	else if(a[i]>='A'&&a[i]<='Z')
    	{
    		a[i] +=1;
    		cout<<static_cast<int>(a[i])<<endl;
    	}
    
    	return 0;
    }

（3）结果

![20190411160203697.png][]

![20190411160212660.png][]

**2、分段函数的计算**

（1）算法

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM5NTY0NTU1_size_16_color_FFFFFF_t_70 1][]

（2）程序

#include <iostream>
    using namespace std;
    int main()
    {
    	double x,y;
    	cout<<"Enter a x = ";
    	cin>>x;
        if(x<1&&x>0)
    	{
    	y=3-2*x;
    	cout<<"y = "<<y<<endl;}
        else if(x>=1&&x<5)
       	{
    	y=2/(4*x)+1;
       	cout<<"y = "<<y<<endl;}
       	else if(x>=5&&x<10)
    	{
    	y=x*x;
        cout<<"y = "<<y<<endl;}
        else if(x<=0||x>=10)
    	  cout<<"x isn't in the area ."<<endl;
    
    	return 0;
    }

（3）结果

![20190411160753602.png][]

![20190411160804722.png][]

![20190411160815311.png][]

![2019041116082669.png][]

**3、三角形周长的计算**

（1）算法

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM5NTY0NTU1_size_16_color_FFFFFF_t_70 2][]

（2）程序

#include <iostream>
    using namespace std;
    int main()
    {
    	double a , b , c , L;
    	cout<<"Please enter the three sides a , b , c : "<<endl;
    	cin>>a>>b>>c;
    	L=a+b+c;
    	if((a+c>b&&a+b>c)&&(b+c>a&&b+a>c)&&(c+a>b&&c+b>a)){
            cout<<"The perimeter of the triangle is : "<<L<<endl;
            if(a!=b&&a!=c&&b!=c)
                cout<<"This is not an isosceles triangle"<<endl;
            else
                cout<<"This is an isosceles triangle"<<endl;
        }
    	else
            cout<<"Three sides do not meet the definition of triangle. Please enter the three sides again"<<endl;
    
    	return 0;
    }

（3）结果

![20190411161315768.png][]

![20190411161326253.png][]

![2019041116133562.png][]

**4、计算器**

（1）算法

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM5NTY0NTU1_size_16_color_FFFFFF_t_70 3][]

（2）程序

#include <iostream>
    using namespace std;
    int main()
    {
    	int a , b ;
    	char c;
    	cout<<"Please enter an equation : "<<endl;
    	cin>>a;
    	cin>>c;
    	cin>>b;
    	switch(c)
    	{
    		case '+': cout << a << " + "<< b << " = " << a+b << endl;break;
    		case '-': cout<<a<<" - "<<b<<" = "<<a-b<<endl;break;
    		case '*': cout<<a<<" * "<<b<<" = "<<a*b<<endl;break;
    		case '%': cout<<a<<" % "<<b<<" = "<<a%b<<endl;break;
    		case '/':	{
                            if(b==0)
                                cout<<"It's a wrong divisor ."<<endl;
                            else
                                cout<<a<<" / "<<b<<" = "<<a/b<<endl;break;}
    	    default: cout<<"Please enter a right equation ."<<endl;break;
    	}
    
    	return 0;
    }

（3）结果

![2019041116185288.png][]

![20190411161901409.png][]

![20190411161911369.png][]

![20190411161920213.png][]

[20190411155255817.png]: /images/20220221/5ed9ea5a2b8e4fa799236b74cd30ee1d.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM5NTY0NTU1_size_16_color_FFFFFF_t_70]: /images/20220221/d1b5046afdd4427c8a14ef7d7cd7b423.png
[20190411160203697.png]: /images/20220221/2b21dded6bec45cd8742461c81dc96b0.png
[20190411160212660.png]: /images/20220221/6ba60bc02610461dabdd6bdd7fa53ba4.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM5NTY0NTU1_size_16_color_FFFFFF_t_70 1]: /images/20220221/9ab31961d3674850a5d75dcff7bbe8f7.png
[20190411160753602.png]: /images/20220221/dfe8fb22ec79421b967bf4ff2e0c6c87.png
[20190411160804722.png]: /images/20220221/d7cc11e733ad4b7b80954e0b45441ec9.png
[20190411160815311.png]: /images/20220221/0313fb6d829f4abfbf9c78662275b1b4.png
[2019041116082669.png]: /images/20220221/4a19e09cdaf04c448579f334c7b5f137.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM5NTY0NTU1_size_16_color_FFFFFF_t_70 2]: /images/20220221/042eb40cdee64f79b3793df7e4433d62.png
[20190411161315768.png]: /images/20220221/e5096fb79a964938b2f1aa21b3d9e227.png
[20190411161326253.png]: /images/20220221/b00443c9420048dc8b36421ce0ab89e6.png
[2019041116133562.png]: /images/20220221/4e9303084b414c5598b53ef8267689d8.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM5NTY0NTU1_size_16_color_FFFFFF_t_70 3]: /images/20220221/690efd06f2594a489bb21cb5ddae62d9.png
[2019041116185288.png]: /images/20220221/d29b9afa6d494f4e9662322341f264bb.png
[20190411161901409.png]: /images/20220221/e52f4d5c394e4d7ba3b601066dfbf18a.png
[20190411161911369.png]: /images/20220221/168d94c3a8d84f238701f5d8cf1b093e.png
[20190411161920213.png]: /images/20220221/104e1840e3e84ef2874456e1092f0cc3.png