Homework 3

　　一、问题：

　　Use the following method printPrimes() for questions a–d.

　　二、代码

/******************************************************* 
     * Finds and prints n prime integers 
     * Jeff Offutt, Spring 2003 
     ******************************************************/ 
    public static void printPrimes (int n) 
    { 
        int curPrime; // Value currently considered for primeness 
        int numPrimes; // Number of primes found so far. 
        boolean isPrime; // Is curPrime prime? 
        int [] primes = new int [MAXPRIMES]; // The list of prime numbers. 
        
        // Initialize 2 into the list of primes. 
        primes [0] = 2; 
        numPrimes = 1; 
        curPrime = 2; 
        while (numPrimes < n) 
        { 
            curPrime++; // next number to consider ... 
            isPrime = true; 
            for (int i = 0; i <= numPrimes-1; i++) 
            { // for each previous prime. 
                if (isDivisable(primes[i],curPrime)) 
                { // Found a divisor, curPrime is not prime. 
                    isPrime = false; 
                    break; // out of loop through primes. 
                } 
            } 
            if (isPrime) 
            { // save it! 
                primes[numPrimes] = curPrime; 
                numPrimes++; 
            } 
        } // End while 
        
        // Print all the primes out. 
        for (int i = 0; i <= numPrimes-1; i++) 
        { 
            System.out.println ("Prime: " + primes[i]); 
        } 
    } // end printPrimes

　　三、解答

　　a、数据流图如下：

 

　　b、数组越界时可能会发生错误

　　c、不经过while循环，使得 初始条件n=1

　　d、点覆盖

　　{1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16}

　　边覆盖

　　{(1.2),(2,3),(3,4),(4,5),(5,6),(6,7),(7,5),(6,8),(8,9),(9,10), (9,11),(10,2),(11,2),(2,12),(12,13),(13,14),(14,15),(15,13),(13,16)}

　　主路径覆盖

　　{(1,2,3,4,5,6,7),

　　(1,2,3,4,5,9,10),

　　(1,2,3,4,5,9,11),

　　(1,2,3,4,5,6,8,9,10),

　　(1,2,3,4,5,6,8,9,11),

　　(1,2,12,13,16),

　　(1,2,12,13,14,15),

　　(3,4,5,6,8,9,10,2,12,13,14,15),

　　(3,4,5,6,8,9,10,2,12,13,16),

　　(3,4,5,9,10,2,12,13,14,15),

　　(3,4,5,9,11,2,12,13,14,15),

　　(3,4,5,9,10,2,12,13,16),

　　(3,4,5,9,10,2,12,13,16),

　　(3,4,5,6,8,9,11,2,12,13,14,15),

　　(3,4,5,6,8,9,11,2,12,13,16),

　　(6,7,5,9,10,2,12,13,14,15),

　　(6,7,5,9,10,2,12,13,16),

　　(6,7,5,9,11,2,12,13,14,15),

　　(6,7,5,9,11,2,12,13,16),

　　(14,15,13,16),

　　(13,14,15,13),

　　(5,6,7,5),

　　(2,3,4,5,6,8,9,10,2),

　　(2,3,4,5,6,8,9,11,2),

　　(2,3,4,5,9,10,2)

　　(2,3,4,5,9,11,2)}

 

　　D、上次上机实验的判断三角形的程序

　　因为三角形的种类有三种，外加一种判断输入参数是否为正整数的返回值，因此主路径测试需求有四个，测试四组用例(2,2,2)，（2,3,3），（2,3,4），（-2,5，-6）。

即可完整覆盖，覆盖率达到100%；