sec-operator.ptx

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<section xml:id="sec-operator" xmlns:xi="http://www.w3.org/2001/XInclude">
  <title>Operators</title>

  <objectives>
    <ul>
      <li>Learn about four main types of operators.</li>
      <li>Understand assignment operators through an example.</li>
    </ul>
  </objectives>

  <introduction>

    <definition xml:id="def-operator">
      <idx><h>Definitions</h><h>of operators</h></idx>
      <statement>
        <p>
          In programming, an <term>operator</term> is a symbol or keyword that describes a specific assignment or a mathematical, relational, or logical operation.
        </p>
        <p>
          In other words, an operator describes an interaction between data.
        </p>
      </statement>
    </definition>
    
    <p>
      Previously, the two operators <c>=</c> and <c>+</c> often show up in examples. Let's take a look at the most basic operators.
    </p>
  </introduction>

  <subsection xml:id="subsec-op-arithmetic">
    <title>Arithmetic Operators</title>

    <p>
      The four most basic arithmetic operators are:
    </p>

    <aside>
      <title>Try It Out</title>
      
      <p>
        What operators do you think work with <xref ref="subsec-list" text="title" />?
      </p> 
    </aside>

    <sage language="python">
      <input>
        print(5 + 3) # Addition
        print(5 - 3) # Subtraction
        print(5 * 3) # Multiplication
        print(5 / 3) # Division

        # String concatenation
        print("string 1 " + "string 2")
      </input>
    </sage>
    <problem>
      <pre>
        8
        2
        15
        1.6666666666666667
        string 1 string 2
      </pre>
    </problem>
    <investigation>
      <idx><h>Code examples</h><h>arithmetic operators</h></idx>
      <idx><h>Code examples</h><h>string concatenation</h></idx>
      <p></p>
      <p>
        The first four lines work just the same as mathematical operations.
      </p>
      <p>
        In line 7, the operator <c>+</c> represents string concatenation (technically not arithmetic but I don't know where else to put it lol).
      </p>
    </investigation>
    
    <p>
      Some less popular operators are:
    </p>

    <sage language="python">
      <input>        
        print(5 // 3) # Floor division
        print(5 ** 3) # Exponentiation
        print(5 % 3) # Modulus
      </input>
    </sage>
    <problem>
      <pre>
        1
        125
        2
      </pre>
    </problem>
    <investigation>
      <idx><h>Code examples</h><h>arithmetic operations</h></idx>
      <p></p>
      <p>
        You can look them up on the Internet to see how they work.
      </p>
    </investigation>

    <p>
      And you should always keep in mind <xref ref="def-dtype-interaction"/>.
    </p>
    
  </subsection>

  <subsection xml:id="subsec-op-assignment">
    <title>Assignment Operators</title>

    <p>
      You've seen <c>=</c> being used very frequently. This is the most important <term>assignment operator</term> that you need to understand.
    </p>

    <definition xml:id="def-op-assignment">
      <idx><h>Definitions</h><h>of assignment operations</h></idx>
      <statement>
        <p>
          An <term>assignment operator</term> is used to declare or update a variable.
        </p>
        <p>
          The value of a variable changes <em>if and only if</em> an assignment operator is used.
        </p>
      </statement>
    </definition>
    
    <note>
      <idx><h>Notes</h><h>on equality</h></idx>
      <p>
        In programming, the assignment operator <c>=</c> should never be associated with equality.
      </p>
    </note>

    <p>For example (using CodeLens is recommended):</p>

    <program language="python" interactive="activecode">
      <input>
        a = 5
        print(a)

        a + 1
        print(a)

        a = a + 1
        print(a)
      </input>
    </program>
    <problem>
      <pre>
        5
        5
        6
      </pre>
    </problem>
    <investigation>
      <idx><h>Code examples</h><h>declaration</h></idx>
      <idx><h>Code examples</h><h>assignment</h></idx>
      <idx><h>Code examples</h><h>updating variables</h></idx>
      <p></p>
      <p>
        Firstly, we declare <c>a</c> and give it the value <c>5</c>.
      </p>
      <p>
        In line 4, we have <c>a + 1</c>, but when we access the value of <c>a</c> in line 5, we still get <c>5</c>.
      </p>
      <p>
        In line 7, we <em>update</em> the variable with <c>a = a + 1</c>. Therefore, in line 8 <c>a</c> has a value of <c>6</c>.
      </p>
    </investigation>
    
    <p>
      <idx><h>Notes</h><h>on assignment operators</h></idx>
      Theoretically, <c>=</c> is the only assignment operator you need to know. But we also have others that serve as shorthands:
    </p>

    <aside>
      <title>Try It Out</title>
      
      <p>
        Try using these.
      </p>
    </aside>

    <p>
      <dl>
        <li>
          <title><c>x += 5</c></title>
          <p>
            Is equivalent to <c>x = x + 5</c> 
          </p>
        </li>
        <li>
          <title><c>x -= 5</c></title>
          <p>
            Is equivalent to <c>x = x - 5</c> 
          </p>
        </li>
        <li>
          <title><c>x *= 5</c></title>
          <p>
            Is equivalent to <c>x = x * 5</c> 
          </p>
        </li>
        <li>
          <title><c>x /= 5</c></title>
          <p>
            Is equivalent to <c>x = x / 5</c> 
          </p>
        </li>
      </dl>
    </p>
    
  </subsection>

  <subsection xml:id="subsec-op-relational">
    <title>Relational Operators</title>

    <p>
      <term>Relational operators</term> are mostly used in conditional statements, so they will be described in more detail in <xref ref="sec-conditional" text="type-local"/>.
    </p>

    <aside>
      <title>Topic(s) you might be interested in</title>
      <p>
        <ul>
          <li>
            <p>
              <idx><h>Links</h><h>Python = vs ==</h></idx>
              <url href="https://www.google.com/search?q=Python+=+vs+==" visual="google.com/search?q=Python+=+vs+==">"Python = vs =="</url>
            </p>
          </li>
        </ul>
      </p> 
    </aside>

    <p>
      <idx><h>Overviews</h><h>of relational operators</h></idx>
      As an overview:

      <dl>
        <li>
          <title><c>x == y</c></title>
          <p>
            Returns <c>True</c> if x equals y
          </p>
          <p>
            Returns <c>False</c> if x does <em>not</em> equal y
          </p>
        </li>
        <li>
          <title><c>x != y</c></title>
          <p>
            Opposite to <c>x == y</c>
          </p>
        </li>
        <li>
          <title><c>x &lt; y</c></title>
          <p>
            Returns <c>True</c> if x is less than y
          </p>
          <p>
            Returns <c>False</c> if x is greater than or equal to y
          </p>
        </li>
        <li>
          <title><c>x &gt; y </c></title>
          <p>
            Returns <c>True</c> if x is greater than y
          </p>
          <p>
            Returns <c>False</c> if x is less than or equal to y
          </p>
        </li>
        <li>
          <title><c>x &lt;= y </c></title>
          <p>
            Opposite to <c>x &gt; y</c> 
          </p>
        </li>
        <li>
          <title><c>x &gt;= y</c></title>
          <p>
            Opposite to <c>x &lt; y</c> 
          </p>
        </li>
      </dl>
    </p>
    
  </subsection>

  <subsection xml:id="subsec-op-logical">
    <title>Logical Operators</title>
    
    <p>
      <term>Logical operators</term> are mostly used in conditional statements, so they will be described in more detail in <xref ref="sec-conditional" text="type-local"/>.
    </p>

    <p>
      <idx><h>Overviews</h><h>of logical operators</h></idx>
      As an overview:
      <dl>
        <li>
          <title><c>x and y</c></title>
          <p>
            Returns <c>True</c> if both statements are <c>True</c>
          </p>
          <p>
            Returns <c>False</c> if at least one statement is <c>False</c>
          </p>
        </li>
        <li>
          <title><c>x or y</c></title>
          <p>
            Returns <c>True</c> if at least one statement is <c>True</c>
          </p>
          <p>
            Returns <c>False</c> if both statements are <c>False</c>
          </p>
        </li>
        <li>
          <title><c>not x</c></title>
          <p>
            Reverses the Boolean
          </p>
          <p>
            Returns <c>True</c> if x is equal to <c>False</c> and vice-versa.
          </p>
        </li>
      </dl>
    </p>
    
  </subsection>

  <conclusion>
    <p>
      <cd>
      </cd>
    </p>

    <exploration>
      <title>Basic Programming <mdash /> Part 8: Operators</title>
      <idx><h>Videos</h><h>part 08</h></idx>
    
      <p>
        Coming soon.
      </p>
      
      <video youtubeplaylist="PLBLdRr-v59vwnKvmvLtcgmAnsb2K1Ta_M" />
      
    </exploration>

  </conclusion>

</section>