C++ primer plus(第六版)编程练习答案第5章循环和关系表达式

妖狐艹你老母 2024-03-24 08:33 75阅读 0赞

## 一、程序清单 ##

## forloop.cpp ##

// forloop.cpp -- introducing the for loop
    #include <iostream>
    int main()
    {
    	using namespace std;
    	int i;  // create a counter
    //   initialize; test ; update
    	for (i = 0; i < 5; i++)
    		cout << "C++ knows loops.\n";
    	cout << "C++ knows when to stop.\n";
    	// cin.get();
    	return 0;
    }

执行结果：

C++ knows loops.
    C++ knows loops.
    C++ knows loops.
    C++ knows loops.
    C++ knows loops.
    C++ knows when to stop.

## num\_test.cpp ##

// num_test.cpp -- use numeric test in for loop
    #include <iostream>
    int main()
    {
    	using namespace std;
    	cout << "Enter the starting countdown value: ";
    	int limit;
    	cin >> limit;
    	int i;
    	for (i = limit; i; i--)     // quits when i is 0
    		cout << "i = " << i << "\n";
    	cout << "Done now that i = " << i << "\n";
    	// cin.get();
    	// cin.get();
    	return 0;
    }

执行结果：

Enter the starting countdown value: 0
    Done now that i = 0

## express.cpp ##

// express.cpp -- values of expressions
    #include <iostream>
    int main()
    {
    	using namespace std;
    	int x;
    
    	cout << "The expression x = 100 has the value ";
    	cout << (x = 100) << endl;
    	cout << "Now x = " << x << endl;
    	cout << "The expression x < 3 has the value ";
    	cout << (x < 3) << endl;
    	cout << "The expression x > 3 has the value ";
    	cout << (x > 3) << endl;
    	cout.setf(ios_base::boolalpha);   //a newer C++ feature
    	cout << "The expression x < 3 has the value ";
    	cout << (x < 3) << endl;
    	cout << "The expression x > 3 has the value ";
    	cout << (x > 3) << endl;
    	/// cin.get();
    	return 0;
    }

执行结果：

The expression x = 100 has the value 100
    Now x = 100
    The expression x < 3 has the value 0
    The expression x > 3 has the value 1
    The expression x < 3 has the value false
    The expression x > 3 has the value true

## **formore.cpp**  ##

// formore.cpp -- more looping with for
    #include <iostream>
    const int ArSize = 16;      // example of external declaration
    int main()
    {
        long long factorials[ArSize];
        factorials[1] = factorials[0] = 1LL;
        for (int i = 2; i < ArSize; i++)
            factorials[i] = i * factorials[i-1];
        for (int i = 0; i < ArSize; i++)
            std::cout << i << "! = " << factorials[i] << std::endl;
    	// std::cin.get();
        return 0;
    }

执行结果：

0! = 1
    1! = 1
    2! = 2
    3! = 6
    4! = 24
    5! = 120
    6! = 720
    7! = 5040
    8! = 40320
    9! = 362880
    10! = 3628800
    11! = 39916800
    12! = 479001600
    13! = 6227020800
    14! = 87178291200
    15! = 1307674368000

## bigstep.cpp ##

// bigstep.cpp -- count as directed
    #include <iostream>
    int main()
    {
    	using std::cout;    // a using declaration
        using std::cin;
        using std::endl;;
        cout << "Enter an integer: ";
        int by;
        cin >> by;
        cout << "Counting by " << by << "s:\n";
        for (int i = 0; i < 100; i = i + by)
            cout << i << endl;
        // cin.get();
        // cin.get();
        return 0;
    }

执行结果：

Enter an integer: 17
    Counting by 17s:
    0
    17
    34
    51
    68
    85

## forstr1.cpp ##

// forstr1.cpp -- using for with a string
    #include <iostream>
    #include <string>
    int main()
    {
        using namespace std;
        cout << "Enter a word: ";
        string word;
        cin >> word;
    
        // display letters in reverse order
        for (int i = word.size() - 1; i >= 0; i--)
            cout << word[i];
        cout << "\nBye.\n";
        // cin.get();
        // cin.get();
        return 0; 
    }

执行结果：

Enter a word: animal
    lamina
    Bye.

## plus\_one.cpp ##

// plus_one.cpp -- the increment operator
    #include <iostream>
    int main()
    {
        using std::cout;
        int a = 20;
        int b = 20;
    
        cout << "a   = " << a << ":   b = " << b << "\n";
        cout << "a++ = " << a++ << ": ++b = " << ++b << "\n";
        cout << "a   = " << a << ":   b = " << b << "\n";
        // std::cin.get();
    	return 0;
    }

执行结果：

a   = 20:   b = 20
    a++ = 20: ++b = 21
    a   = 21:   b = 21

block.cpp

// block.cpp -- use a block statement
    #include <iostream>
    int main()
    {
    	using namespace std;
    	cout << "The Amazing Accounto will sum and average ";
    	cout << "five numbers for you.\n";
    	cout << "Please enter five values:\n";
    	double number;
    	double sum = 0.0;
    	for (int i = 1; i <= 5; i++)
    	{                                   // block starts here
    		cout << "Value " << i << ": ";
    		cin >> number;
    		sum += number;
    	}                                   // block ends here
    	cout << "Five exquisite choices indeed! ";
    	cout << "They sum to " << sum << endl;
    	cout << "and average to " << sum / 5 << ".\n";
    	cout << "The Amazing Accounto bids you adieu!\n";
    	// cin.get();
    	// cin.get();
    	return 0;
    }

执行结果：

a   = 20:   b = 20
    a++ = 20: ++b = 21
    a   = 21:   b = 21

## forstr2.cpp ##

// forstr2.cpp -- reversing an array
    #include <iostream>
    #include <string>
    int main()
    {
    	using namespace std;
    	cout << "Enter a word: ";
    	string word;
    	cin >> word;
    
    	// physically modify string object
    	char temp;
    	int i, j;
    	for (j = 0, i = word.size() - 1; j < i; --i, ++j)
    	{                       // start block
    		temp = word[i];
    		word[i] = word[j];
    		word[j] = temp;
    	}                       // end block
    	cout << word << "\nDone\n";
    	// cin.get();
    	// cin.get();
    	return 0;
    }

执行结果：

Enter a word: stressed
    desserts
    Done

## equal.cpp ##

// equal.cpp -- equality vs assignment
    #include <iostream>
    int main()
    {
        using namespace std;
        int quizscores[10] =
            { 20, 20, 20, 20, 20, 19, 20, 18, 20, 20};
    
        cout << "Doing it right:\n";
        int i;
        for (i = 0; quizscores[i] == 20; i++)
            cout << "quiz " << i << " is a 20\n";
    // Warning: you may prefer reading about this program
    // to actually running it.
        cout << "Doing it dangerously wrong:\n";
        for (i = 0; quizscores[i] = 20; i++)
            cout << "quiz " << i << " is a 20\n";
    	// cin.get();
        return 0;
    }

执行结果：

![watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBA6ZW_5rKZ5pyJ6IKl6bG8_size_20_color_FFFFFF_t_70_g_se_x_16][]

## compstr1.cpp ##

// compstr1.cpp -- comparing strings using arrays
    #include <iostream>
    #include <cstring>     // prototype for strcmp()
    int main()
    {
    	using namespace std;
    	char word[5] = "?ate";
    
    	for (char ch = 'a'; strcmp(word, "mate"); ch++)
    	{
    		cout << word << endl;
    		word[0] = ch;
    	}
    	cout << "After loop ends, word is " << word << endl;
    	// cin.get();
    	return 0;
    }

执行结果：

?ate
    aate
    bate
    cate
    date
    eate
    fate
    gate
    hate
    iate
    jate
    kate
    late
    After loop ends, word is mate

## compstr2.cpp ##

// compstr2.cpp -- comparing strings using arrays
    #include <iostream>
    #include <string>     // string class
    int main()
    {
    	using namespace std;
    	string word = "?ate";
    
    	for (char ch = 'a'; word != "mate"; ch++)
    	{
    		cout << word << endl;
    		word[0] = ch;
    	}
    	cout << "After loop ends, word is " << word << endl;
    	// cin.get();
    	return 0;
    }

执行结果：

?ate
    aate
    bate
    cate
    date
    eate
    fate
    gate
    hate
    iate
    jate
    kate
    late
    After loop ends, word is mate

## while.cpp ##

// while.cpp -- introducing the while loop
    #include <iostream>
    const int ArSize = 20;
    int main()
    {
        using namespace std;
        char name[ArSize];
    
        cout << "Your first name, please: ";
        cin >> name;
        cout << "Here is your name, verticalized and ASCIIized:\n";
        int i = 0;                  // start at beginning of string
        while (name[i] != '\0')     // process to end of string
        {
            cout << name[i] << ": " << int(name[i]) << endl;
            i++;                    // don't forget this step
        }
        // cin.get();
        // cin.get();
        return 0; 
    }

执行结果：

Your first name, please: Muffy
    Here is your name, verticalized and ASCIIized:
    M: 77
    u: 117
    f: 102
    f: 102
    y: 121

## waiting.cpp ##

// waiting.cpp -- using clock() in a time-delay loop
    #include <iostream>
    #include <ctime> // describes clock() function, clock_t type
    int main()
    {
        using namespace std;
        cout << "Enter the delay time, in seconds: ";
        float secs;
        cin >> secs;
        clock_t delay = secs * CLOCKS_PER_SEC;  // convert to clock ticks
        cout << "starting\a\n";
        clock_t start = clock();
        while (clock() - start < delay )        // wait until time elapses
            ;                                   // note the semicolon
        cout << "done \a\n";
        // cin.get();
        // cin.get();
        return 0; 
    }

执行结果：

Your first name, please: Muffy
    Here is your name, verticalized and ASCIIized:
    M: 77
    u: 117
    f: 102
    f: 102
    y: 121

## dowhile.cpp ##

// dowhile.cpp -- exit-condition loop
    #include <iostream>
    int main()
    {
    	using namespace std;
    	int n;
    
    	cout << "Enter numbers in the range 1-10 to find ";
    	cout << "my favorite number\n";
    	do
    	{
    		cin >> n;       // execute body
    	} while (n != 7);   // then test
    	cout << "Yes, 7 is my favorite.\n";
    	// cin.get();
    	// cin.get();
    	return 0;
    }

执行结果：

Enter numbers in the range 1-10 to find my favorite number
    9
    4
    7
    Yes, 7 is my favorite.

## textin1.cpp ##

// textin1.cpp -- reading chars with a while loop
    #include <iostream>
    int main()
    {
    	using namespace std;
    	char ch;
    	int count = 0;      // use basic input
    	cout << "Enter characters; enter # to quit:\n";
    	cin >> ch;          // get a character
    	while (ch != '#')   // test the character
    	{
    		cout << ch;     // echo the character
    		++count;        // count the character
    		cin >> ch;      // get the next character
    	}
    	cout << endl << count << " characters read\n";
    	// get rid of rest of line
    		 // while (cin.get() != '\n')
    			// ;
    	//cin.get();
    	return 0;
    }

执行结果：

Enter characters; enter # to quit:
    see ken run#really fast
    seekenrun
    9 characters read

## textin2.cpp ##

// textin2.cpp -- using cin.get(char)
    #include <iostream>
    int main()
    {
        using namespace std;
        char ch;
        int count = 0;
    
        cout << "Enter characters; enter # to quit:\n";
        cin.get(ch);        // use the cin.get(ch) function
        while (ch != '#')
        {
            cout << ch;
            ++count;
            cin.get(ch);    // use it again
        }
        cout << endl << count << " characters read\n";
    // get rid of rest of line
        // while (cin.get() != '\n')
        //    ;
        //cin.get();
        return 0; 
    }

执行结果：

Enter characters; enter # to quit:
    Did you use a #2 pencil?
    Did you use a
    14 characters read

## textin3.cpp ##

// textin3.cpp -- reading chars to end of file
    #include <iostream>
    int main()
    {
        using namespace std;
        char ch;
        int count = 0;
        cin.get(ch);        // attempt to read a char
        while (cin.fail() == false)  // test for EOF
        {
            cout << ch;     // echo character
            ++count;
            cin.get(ch);    // attempt to read another char
        }
        cout << endl << count << " characters read\n";
        return 0; 
    }

执行结果：

The green bird sings in the winter.
    The green bird sings in the winter.
    Yes,but the crow files in the dawn.
    Yes,but the crow files in the dawn.
    ^Z
    
    72 characters read

## textin4.cpp ##

// textin4.cpp -- reading chars with cin.get()
    #include <iostream>
    int main(void)
    {
        using namespace std;
        int ch;                         // should be int, not char
        int count = 0;
    
        while ((ch = cin.get()) != EOF) // test for end-of-file
        {
            cout.put(char(ch));
            ++count;
        }
        cout << endl << count << " characters read\n";
    	return 0; 
    }

执行结果：

The sullen mackerel sulks in the shadowy shallows.
    The sullen mackerel sulks in the shadowy shallows.
    Yes,but the blue bird of happiness harbors secrets.
    Yes,but the blue bird of happiness harbors secrets.
    ^Z
    
    103 characters read

## nested.cpp ##

// nested.cpp -- nested loops and 2-D array
    #include <iostream>
    const int Cities = 5;
    const int Years = 4;
    int main()
    {
    	using namespace std;
    	const char * cities[Cities] =   // array of pointers
    	{                               // to 5 strings
    		"Gribble City",
    		"Gribbletown",
    		"New Gribble",
    		"San Gribble",
    		"Gribble Vista"
    	};
    
    	int maxtemps[Years][Cities] =   // 2-D array
    	{
    		{96, 100, 87, 101, 105},   // values for maxtemps[0]
    		{96, 98, 91, 107, 104},   // values for maxtemps[1]
    		{97, 101, 93, 108, 107}, // values for maxtemps[2]
    		{98, 103, 95, 109, 108}   // values for maxtemps[3]
    	};
    
    	cout << "Maximum temperatures for 2008 - 2011\n\n";
    	for (int city = 0; city < Cities; ++city)
    	{
    		cout << cities[city] << ":\t";
    		for (int year = 0; year < Years; ++year)
    			cout << maxtemps[year][city] << "\t";
    		cout << endl;
    	}
    	// cin.get();
    	return 0;
    }

执行结果：

Maximum temperatures for 2008 - 2011
    
    Gribble City:   96      96      97      98
    Gribbletown:    100     98      101     103
    New Gribble:    87      91      93      95
    San Gribble:    101     107     108     109
    Gribble Vista:  105     104     107     108

## 二、复习题 ##

1.入口条件循环和出口条件循环之间的区别是什么？各种c++循环分别属于其中的哪一种？

入口循环就是程序在执行循环体中的语句之前先检查循环条件；出口循环是在执行循环体中的语句之后检查循环条件。for循环和while循环都是入口条件循环；do while循环为出口条件循环。

2.如果下面的代码片段是有效程序的组成部分，它将打印什么内容？

int i;
    for(i=0;i<5;i++)
          cout<<i;
    cout<<endl;

打印内容：`01234`

3.如果下面的代码片段是有效程序的组成部分，它将打印什么内容？

int j;
    for(j=0;j<11;j+=3)
        cout<<j;
    cout<<endl<<j<<endl;

打印内容：  
`0369`  
`12`

4.如果下面代码是有效程序的组成部分，它将打印什么内容？

int j=5;
    while(++j<9)
        cout<<j++<<endl;

打印内容：  
`6`  
`8`

5.如果下面代码是有效程序的组成部分，它将打印什么内容？

int k=8;
    do
        cout<<"k="<<k<<endl;
    while(k++<5);

打印内容：  
`k=8`

6.编写一个打印1、2、4、8、16、32、64的for循环，每轮循环都将计数变量的值乘以2。

int i;
    for(i=1;i<=64;i*=2)
        cout<<i<<" "；

7.如何在循环体中包括多条语句？

将语句放在一对大括号中形成一个复合语句或代码块。

8.下面的语句是否有效？如果无效，原因是什么？如果有效，它将完成什么工作？

a.`int x={1,024}`  
b.`int y=1,024;`  
语句a是有效的，表达式1,024为逗号表达式，该表达时的右侧表达式的值，由于024为8进制数，对应的十进制数为20，因此x的值应为20，即x=20。  
语句b也是有效的，但是逗号运算符的优先级低于赋值运算符，因此b中表达式等效为`(int y=1),024;`。

9.在查看输入方面，cin>>ch同cin.get(ch)和ch=cin.get()有什么不同？

`cin>>ch`将跳过空格、换行符和制表符，其他两种格式将读取这些字符。

## 三、编程练习 ##

1.编写一个要求用户输入两个整数的程序。该程序将计算并输出这两个整数之间（包括这两个整数）所有整数的和。这里假设先输入较小的整数。例如，如果用户输入的是2和9，则程序将指出2~9之间所有整数的和为44。

#include<iostream>
    using namespace std;
    int main()
    {
        int a, b, sum = 0;
        cout << "Please enter two integers(enter the smaller integer first)." << endl;
        cout << "The first integer : _\b";
        cin >> a;
        cout << "The second integer: _\b";
        cin >> b;
        for (int i = a; i <= b; i++)
            sum += i;
        cout << "The sum of integers between "<<a<<" and "<<b<<" is : " << sum << endl;
        system("pause");
        return 0;
    }

2.使用array对象（而不是数组）和long double（而不是long long）重新编写程序清单5.4，并计算100！的值。

> Listing 5.4 formore.cpp
> 
> --------------------
> 
> `// formore.cpp -- more looping with for`  
> `#include <iostream>`  
> `const int ArSize = 16; // example of external declaration`  
> `int main()`  
> `{`  
>     `long long factorials[ArSize];`  
>     `factorials[1] = factorials[0] = 1LL;`  
>     `for (int i = 2; i < ArSize; i++)`  
>     `factorials[i] = i * factorials[i-1];`  
>     `for (int i = 0; i < ArSize; i++)`  
>     `std::cout << i << "! = " << factorials[i] << std::endl;`  
>     `return 0;`  
> `}`
> 
> --------------------

编写后程序清单：

#include<iostream>
    #include<array>
    const int ArSize = 16; 
    int main()
    {
        using namespace std;
        array<long double,ArSize>factorials;
        factorials[1] = factorials[0] = 1.0;
        for (int i = 2; i < ArSize; i++)
            factorials[i] = i * factorials[i - 1];
        for (int i = 0; i <ArSize; i++)
            cout << i << "! = " << factorials[i] << endl;
        system("pause");
        return 0;
    }

3.编写一个要求用户输入数字的程序。每次输入后，程序都将报告到目前为止，所有输入的累计和，当用户输入0时，程序结束。

#include<iostream>
    #include<array>
    int main()
    {
        using namespace std;
        double num,sum=0;
        for (int i = 1; i != 0; i=num)
        {
            cout << "Please enter a number(if 0,the end the program.)_\b";
            cin >> num;
            sum += num;
            cout << "At this point, the cumulative sum of the Numbers is : " << sum << endl;
        }
        cout << "Bye" << endl;
        system("pause");
        return 0;
    }

4.Daphne以10%的单利投资了100美元。也就是说，每一年的利润都是投资额的10%，即每年10美元：利息=0.10\*原始存款。而Cleo在第一年投资100美元的盈利是5%--一共得到105美元。下一年的盈利是105美元的5%--即5.25美元，以此类推。请编写一个程序，计算多少年后，Cleo的投资价值超过Daphne的投资价值。并显示此时两个人的投资价值。

#include<iostream>
    int main()
    {
        using namespace std;
        double daphne = 100.0;
        double cleo = 100.0;
        int year;
        for (year = 1; cleo <= daphne; year++)
        {
            daphne += 10.0;
            cleo *= 1.05;
        }
        cout << year << " years later,Cleo's investment is worth more than Daphne's." << endl;
        cout << "Daphne has $" << daphne << endl;
        cout << "Cleo has $" << cleo << endl;
        system("pause");
        return 0;
    }

5.假设要销售《C++ For Fools》一书。请编写一个程序，输入全年中每个月的销售量（图书数量，而不是销售额）。程序通过循环，使用初始化为月份字符串的char\*数组（或string对象数组）逐月进行提示，并将输入数据存储的int数组中。然后，程序计算数组中各元素的总数，并报告这一年的销售情况。

#include<iostream>
    #include<string>
    int main()
    {
        using namespace std;
        string months[12]  = {
            "January", "February", "March", "April", "May", "June",
            "July", "August", "September", "October", "November",
            "December"
        };
        int sales[12];
        int sum = 0;
    
        for (int i = 0; i < 12; i++)
        {
            cout << "Please enter the sales volume for " << months[i] << " : _\b";
            cin >> sales[i];
        }
    
        for (int i = 0; i < 12; i++)
        {
            cout << months[i] << " sales : " << sales[i]<<endl;
            sum += sales[i];
        }
    
        cout << "Annual sales ：" << sum << endl;
        system("pause");
        return 0;
    }

6.完成编程练习5，但这一次使用大的一个二位数组来存储输入---3年中每个月的销售量。程序将报告每年销量以及三年的总销量。

#include<iostream>
    #include<string>
    int main()
    {
        using namespace std;
        string months[12]  = {
            "January", "February", "March", "April", "May", "June",
            "July", "August", "September", "October", "November",
            "December"
        };
        int sales[3][12];
        int sum = 0;
        for (int i = 0; i < 3; i++)
        {
            cout << "Year " << i+1 << ": " << endl;
            for (int f = 0; f < 12; f++)
            {
                cout << "Please enter the sales volume for " << months[f] << " : _\b";
                cin >> sales[i][f];
            }
        }
        for (int j=0; j < 3; j++)
        {
            cout << "*********Year " << j+1 << "*********" << endl;
            for (int i = 0; i < 12; i++)
            {
                cout << months[i] << " sales : " << sales[j][i] << endl;
                sum += sales[j][i];
            }
        }
        cout << "Annual sales ：" << sum << endl;
        system("pause");
        return 0;
    }

7.设计一个名为car的结构，用它存储下述有关汽车的信息：生产商（存在字符数组或string对象中的字符串）、生产年份（整数）。编写一个程序向用户询问有多少辆汽车。随后，程序使用new来创建一个有相应数量的car结构组成的动态数组。接下来，程序提示用户输入每辆车的生产商（可能有多个单词组成）和年份信息。请注意，这需要特别小心，因为它将交替读取数值和字符串。最后，程序将显示每个结构的内容。该程序的运行情况如下：

How many cars do you wish to catalog? 2
    Car #1:
    Please enter the make:Hudson Hornet
    Please enter the year made:1952
    Car #2:
    Please enter the make:Kaiser
    Please enter the year made:1951
    Here is your collection:
    1952 HUdson Hornet
    1951 Kaiser

实现代码：

#include<iostream>
    #include<string>
    using namespace std;
    struct Car {
        string maker;
        int year;
    };
    
    int main()
    {
        int num;
        cout << "How many cars do you wish to catalog? ";
        (cin >> num).get();
        Car *cars=new Car[num];
        for (int i=0; i < num; i++)
        {
            cout << "Car #" << i + 1 << " : " << endl;
            cout << "Please enter the make : ";
            getline(cin ,cars[i].maker);
            cout << "Please enter the year made : ";
            (cin >> cars[i].year).get();
        }
        cout << "Here is your collection:" << endl;
        for (int i = 0; i < num; i++)
            cout << cars[i].year << " " << cars[i].maker << endl;
        delete []cars;
        system("pause");
        return 0;
    }

8.编写一个程序，它使用一个char数组和循环来每次读取一个单词，直到用户输入done为止。随后，该程序指出用户输入多少个单词（不包含done）。下面是程序的运行情况：

Enter words(to stop,type the word done):
    anteater birthday category dumpster
    envy finagle geometry done for sure
    You entered a total of 7words.

您应在程序中包含头文件cstring，并使用strcmp()来进行比较测试。

实现代码：

#include<iostream>
    #include<cstring>
    using namespace std;
    
    int main()
    {
        char word[20];
        cout << "Enter words(to stop,type the word done):" << endl;
        cin >> word;
        int num = 0;
        while (strcmp("done", word))
        {
            num++;
            cin >> word;
        }
        cout << "You entered a total of " << num << " words." << endl;
        system("pause");
        return 0;
    }

9.编写一个满足前一个练习的中描述的程序，但使用string对象而不是字符数组。请在程序中包含头文件string，并使用关系运算符来进行比较测试。

#include<iostream>
    #include<string>
    using namespace std;
    
    int main()
    {
        string word;
        cout << "Enter words(to stop,type the word done):" << endl;
        cin >> word;
        int num = 0;
        while ( word.compare("done"))
        {
            num++;
            cin >> word;
        }
        cout << "You entered a total of " << num << " words." << endl;
        system("pause");
        return 0;
    }

10.编写一个使用嵌套循环的程序，要求用户输入一个值，指出要显示多少行。然后，程序将显示相应行数的型号，其中第一行包括一个星号，第二行包括两个星号，以此类推。每一行包含的字符数等于用户指定的行数，在星号不够的情况下，在星号前面加句点。程序的运行情况如下：

Enter number of row : 5
    ....*
    ...**
    ..***
    .****
    *****

代码实现：

#include<iostream>
    using namespace std;
    
    int main()
    {
        int row;
        cout << "Enter number of rows : ";
        cin >> row;
        for (int i = 0; i < row; i++)
        {
            for (int j = 0; j < row; j++)
            {
                if (i < row -j-1)
                    cout << '.';
                else
                    cout << '*';
            }
            cout << endl;
        }
        system("pause");
        return 0;
    }

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