PreTeXt Sample Book Abstract Algebra (SAMPLE ONLY)

  <section xml:id="code-lens">

    <title>Code Lens</title>

    <p>
CodeLens is an interactive tool for following program execution, much like a debugger, without the ability to influence flow control or variable values.  For use without a server, traces must be computed beforehand.  First, we have some trivial programs, to provide minimal testing.
    </p>

    <listing xml:id="program-codelens-python">

      <title>A Python program, stepable with CodeLens</title>

      <program label="python-hello-world-code-lens" interactive="codelens" language="python">

        <code>
                print('Hello, World!')
        </code>

      </program>

    </listing>

    <listing xml:id="program-codelens-c">

      <title>An C program, stepable with CodeLens</title>

      <program label="c-hello-world-code-lens" interactive="codelens" language="c">

        <code>
                #include &lt;stdio.h&gt;
                int main(void)
                {
                    puts("Hello, World!");
                }
        </code>

      </program>

    </listing>

    <listing xml:id="program-codelens-java">

      <title>A Java program, stepable with CodeLens</title>

      <program label="java-hello-world-code-lens" interactive="codelens" language="java">

        <code>
                public class HelloWorld {
                    public static void main(String[] args) {
                        System.out.println("Hello, World!");
                    }
                }
        </code>

      </program>

    </listing>

    <p>
      Codelens interactives can be given one or more checkpoints where the user is asked a question as the code is executed:
    </p>

    <listing xml:id="program-codelens-python-questions">

      <title>A Python program, stepable with CodeLens, with questions</title>

      <program label="python-code-lens-questions" interactive="codelens" language="python" include-source="yes">

        <code>
                def foo(n):
                    n = n + 1
                    return n
                x = 7
                y = x // 3
                z = foo(y)
        </code> <checkpoint line="4" answer="x"> <prompt>What variable is being assigned to?</prompt> </checkpoint> <checkpoint line="5" answer-variable="globals.y"> <prompt>What value will be assigned to <c>y</c>?</prompt>

        <feedback>

          <c>//</c> does integer division

        </feedback>

        </checkpoint> <checkpoint line="3" answer-variable="current_frame.n"> <prompt>What value will be returned?</prompt>

        <feedback>
What is <c>n</c> right now?
        </feedback>

        </checkpoint>

      </program>

    </listing>

    <p>
If a Codelens contains checkpoints, it is also possible to make it into an exercise. For use on Runestone, there should be an <attr>label</attr> on the exercise:
    </p>

    <exercise label="program-codelens-cpp-questions">

      <title>A C++ program as CodeLens exercise</title>

      <statement>
Run the codelens and answer the questions it asks.
      </statement>

      <program interactive="codelens" language="cpp" include-source="yes">

                <code>
                  int foo() {
                      int x = 2;
                      int y = ++x;
                      return y;
                  }
                  int main() {
                      int x = foo();
                      while (x &lt; 20) {
                        x *= 2;
                      }
                  }
                  
        </code> <checkpoint line="3" answer="3"> <prompt>What value will be assigned to <c>y</c>?</prompt>

        <feedback>

          <c>++</c> has precedence over <c>=</c>

        </feedback>

        </checkpoint> <checkpoint line="9" answer-variable="current_frame.x"> <prompt>What value will be assigned to <c>x</c>?</prompt>

        <feedback>
We are doubling it
        </feedback>

        </checkpoint>

      </program>

    </exercise>

    <p>
Now some moderately more complicated programs to find the prime numbers less than <m>20</m>.  We do not vouch for the quality of these, or even their correctness!
    </p>

    <listing xml:id="sieve-python">

      <title><url href="https://www.tutorialspoint.com/python-program-for-sieve-of-eratosthenes" visual="www.tutorialspoint.com/python-program-for-sieve-of-eratosthenes">Sieve of Eratosthenes</url>, Java</title>

      <program label="sieve-codelens-python" interactive="codelens" language="python" starting-step="73" include-source="yes">

                <code>
                def SieveOfEratosthenes(n):
                   # array of type boolean with True values in it
                   prime = [True for i in range(n + 1)]
                   p = 2
                   while (p * p &lt;= n):
                      # If it remain unchanged it is prime
                      if (prime[p] == True):
                         # updating all the multiples
                         for i in range(p * 2, n + 1, p):
                            prime[i] = False
                      p += 1
                   prime[0]= False
                   prime[1]= False
                   # Print
                   for p in range(n + 1):
                      if prime[p]:
                         print (p,end=" ")
                # main
                if __name__=='__main__':
                   n = 20
                   print ("The prime numbers smaller than or equal to", n,"is")
                   SieveOfEratosthenes(n)
                
        </code>

      </program>

    </listing>

    <listing xml:id="sieve-cpp">

      <title><url href="https://www.tutorialspoint.com/cplusplus-program-to-implement-sieve-of-eratosthenes-to-generate-prime-numbers-between-given-range" visual="www.tutorialspoint.com/cplusplus-program-to-implement-sieve-of-eratosthenes-to-generate-prime-numbers-between-given-range">Sieve of Eratosthenes</url>, C++</title>

      <program label="sieve-codelens-cpp" interactive="codelens" language="cpp">

        <code> 
        #include &lt;stdio.h&gt;
        const int len = 20;
        int main() {
        int arr[20] = {0};
        for (int i = 2; i &lt; len; i++) {
        for (int j = i * i; j &lt; len; j+=i) {
        arr[j - 1] = 1;
        }
        }
        for (int i = 1; i &lt; len; i++) {
        if (arr[i - 1] == 0)
        printf(" %d", i);
        }
        }
        
        </code>

      </program>

    </listing>

    <listing xml:id="sieve-java">

      <title><url href="https://www.tutorialspoint.com/Sieve-of-Eratosthenes-in-java" visual="www.tutorialspoint.com/Sieve-of-Eratosthenes-in-java">Sieve of Eratosthenes</url>, Java</title>

      <program label="sieve-codelens-java" interactive="codelens" language="java">

        <code>
        public class SievePrimeFactors  {
        public static void main(String args[]) {
        int num = 20;
        boolean[] bool = new boolean[num];
        for (int i = 0; i&lt; bool.length; i++) {
        bool[i] = true;
        }
        for (int i = 2; i &lt; Math.sqrt(num); i++) {
        if(bool[i] == true) {
        for(int j = (i*i); j &lt; num; j = j+i) {
        bool[j] = false;
        }
        }
        }
        System.out.println("List of prime numbers: ");
        for (int i = 2; i&lt; bool.length; i++) {
        if(bool[i]==true) {
        System.out.println(i);
        }
        }
        }
        }
        
        </code>

      </program>

    </listing>

  </section>