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| <!DOCTYPE html> | ||
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| <html> | ||
| <head> | ||
| <link rel="stylesheet" href="../../main.css"> | ||
| <link rel="stylesheet" href="../main.css"> | ||
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| <title>Computer Science Revision</title> | ||
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| <link rel="icon" type="image/png" href="../icons/logo.svg"/> | ||
| <meta property="og:image" content="../icons/logo.svg" /> | ||
| <meta property="og:image:width" content="256" /> | ||
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| <meta name="viewport" content="width=device-width, initial-scale=1.0"> | ||
| <meta name="description" content="1.02 - Pseudo-code | Computer Science Revision"> | ||
| </head> | ||
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| <body> | ||
| <h1>1.02 – Pseudo-code</h1> | ||
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| <a class="prev-link" href="../1-01-Computational-Thinking/">Previous: 1.01 - Computational Thinking</a> | ||
| <br /> <br /> | ||
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| <p class="definition"> | ||
| <img src="../icons/book.svg" class="icon" /> | ||
| <strong>Pseudo-code</strong> is a way of writing algorithms that reads like code written in actual programming languages. | ||
| </p> | ||
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| <p> | ||
| <b>Pseudo-code is not a real programming language.</b> | ||
| The idea is that pseudo-code clearly shows an algorithm's steps without worrying about the syntax (finer details) of any particular programming language. | ||
| </p> | ||
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| <p><br />There are three basic programming constructs which we use when writing pseudo-code:</p> | ||
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| <p class="definition"> | ||
| <img src="../icons/book.svg" class="icon" /> | ||
| <strong>Sequence</strong> is just a mattter of writing of writing down the steps in the correct order. | ||
| </p> | ||
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| <p class="definition"> | ||
| <img src="../icons/book.svg" class="icon" /> | ||
| <strong>Selection</strong> allows you to choose between multiple options. | ||
| </p> | ||
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| <p>Example 1 shows how an <code>IF</code> statement can be used in pseudo-code.</p> | ||
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| <p class="code"> | ||
| <img src="../icons/code.svg" class="icon" /> | ||
| Example 1 <br /> | ||
| <code> | ||
| age ← <el class="function">USERINPUT</el> <br /> | ||
| <el class="keyword">IF</el> age ≥ <el class="number">18</el> <el class="keyword">THEN</el> <br /> | ||
|   <el class="function">OUTPUT</el> <el class="string">"OK"</el> <br /> | ||
| <el class="keyword">ELSE</el> <br /> | ||
|   <el class="function">OUTPUT</el> <el class="string">"Too young"</el> <br /> | ||
| <el class="keyword">ENDIF</el> | ||
| </code> | ||
| </p> | ||
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| <p class="definition"> | ||
| <img src="../icons/book.svg" class="icon" /> | ||
| <strong>Iteration</strong> means looping. There are three different types of loops in pseudo-code. | ||
| </p> | ||
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| <p>Example 2 shows an algorithm containing a <code>FOR ... ENDFOR</code> loop. The algorithm asks the user for five numbers and outputs their sum.</p> | ||
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| <p class="code"> | ||
| <img src="../icons/code.svg" class="icon" /> | ||
| Example 2 <br /> | ||
| <code> | ||
| total ← <el class="number">0</el> <br /> | ||
| <el class="keyword">FOR</el> count ← <el class="number">1</el> <el class="keyword">TO</el> <el class="number">5</el> <br /> | ||
|   num ← <el class="function">USERINPUT</el> <br /> | ||
|   total ← total + num <br /> | ||
| <el class="keyword">ENDFOR</el> <br /> | ||
| <el class="function">OUTPUT</el> total | ||
| </code> | ||
| </p> | ||
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| <p>Example 3 shows an algorithm containing a <code>REPEAT ... UNTIL</code> loop. The algorithm counts up until the user stops it.</p> | ||
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| <p class="code"> | ||
| <img src="../icons/code.svg" class="icon" /> | ||
| Example 3 <br /> | ||
| <code> | ||
| count ← <el class="number">0</el> <br /> | ||
| <el class="keyword">REPEAT</el> <br /> | ||
|   count ← count + <el class="number">1</el> <br /> | ||
|   <el class="function">OUTPUT</el> count <br /> | ||
|   end ← <el class="function">USERINPUT</el> <br /> | ||
| <el class="keyword">UNTIL</el> end = <el class="string">"yes"</el> | ||
| </code> | ||
| </p> | ||
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| <p>Example 4 shows an algorithm containing a <code>WHILE ... ENDWHILE</code> loop. The algorithm keeps asking the user for a password until they get it correct.</p> | ||
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| <p class="code"> | ||
| <img src="../icons/code.svg" class="icon" /> | ||
| Example 4 <br /> | ||
| <code> | ||
| password ← <el class="function">USERINPUT</el> <br /> | ||
| <el class="keyword">WHILE</el> password ≠ <el class="string">"Password123"</el> <br /> | ||
|   <el class="function">OUTPUT</el> <el class="string">"Try again"</el> <br /> | ||
|   password ← <el class="function">USERINPUT</el> <br /> | ||
| <el class="keyword">ENDWHILE</el> <br /> | ||
| <el class="function">OUTPUT</el> <el class="string">"Correct password"</el> | ||
| </code> | ||
| </p> | ||
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| <p> | ||
| <code>REPEAT ... UNTIL</code> loops and <code>WHILE ... ENDWHILE</code> loops are very similar, but there are some key differences. | ||
| </p> | ||
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| <p> | ||
| Firstly, <code>REPEAT ... UNTIL</code> loops keep looping <em>until</em> the condition is true, | ||
| whereas <code>WHILE ... ENDWHILE</code> loops keep looping <em>while</em> the condition is true. | ||
| </p> | ||
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| <p> | ||
| Secondly, <code>REPEAT ... UNTIL</code> loops check the condition at the end, so will always run at least once, | ||
| but <code>WHILE ... ENDWHILE</code> loops check their condition at the start, so won't run if the condition starts off as false. | ||
| </p> | ||
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| <p><br />Example 5 shows an algorithm written in pseudo-code.</p> | ||
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| <p class="code"> | ||
| <img src="../icons/code.svg" class="icon" /> | ||
| Example 5 <br /> | ||
| <code> | ||
| total ← <el class="number">1</el> <br /> | ||
| <el class="keyword">FOR</el> num ← <el class="number">1</el> <el class="keyword">TO</el> <el class="number">10</el> <br /> | ||
|   <el class="keyword">IF</el> num MOD <el class="number">2</el> = <el class="number">0</el> <el class="keyword">THEN</el> <br /> | ||
|     total ← total * num <br /> | ||
|   <el class="keyword">ENDIF</el> <br /> | ||
| <el class="keyword">ENDFOR</el> <br /> | ||
| <el class="function">OUTPUT</el> total | ||
| </code> | ||
| </p> | ||
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| <p class="question"> | ||
| <img src="../icons/question.svg" class="icon" /> | ||
| What does the code in Example 5 do? | ||
| </p> | ||
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| <p><i>Hint: <code>num MOD 2</code> means the remainder from dividing <code>num</code> by <code>2</code>.</i><br /> </p> | ||
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| <p class="spoiler"> | ||
| <el class="default">Hover/tap to reveal</el> | ||
| <el class="answer">Multiplies all the even numbers from 1 to 10 and outputs the result.</el> | ||
| </p> | ||
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| <br /> | ||
| <br /> | ||
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| <div id="sub">© Rujul Nayak <el id="year">2024-</el></div> | ||
| <script src="../../year.js"></script> | ||
| </body> | ||
| </html> |
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