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2022-02-15 01:14:58 -05:00
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2020-01-15 23:07:02 -05:00
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<h2>Counting Loop</h2>
<p>Looking at the following example code</p>
<pre><code class="language-java">int i;
for (i = 0; i &lt; 3; i++) { //begin for
System.out.println("i = " + i); //body
} //end for
System.out.println("After loop, i = " + i);</code></pre>
<p><code>i = 0</code> is the initializing statement</p>
<p><code>i &lt; 3</code> is the conditional, that is when the loop ends</p>
<p><code>i++</code> is the increment/decrement</p>
<p><code>i++</code> is synonymous with <code>i = i + 1</code></p>
<p>The initialization statement only occurs once at the beginning of the loop. </p>
<h3>Execution Example</h3>
<p>Let us go through this for loop example</p>
<ul>
<li>Let us set <code>i = 0</code></li>
<li>Is <code>i &lt; 3</code>? Yes execute the body
<ul>
<li>The body executes an output of <code>"i = 0"</code></li>
</ul></li>
<li>Now we increment <code>i ++</code>, i is now 1</li>
<li>Is <code>i &lt; 3</code>? Yes, 1 is less than 3. Execute body
<ul>
<li>The computer prints out <code>"i = 1"</code></li>
</ul></li>
<li>Increment <code>i++</code> i is now 2</li>
<li>Is <code>i &lt; 3</code>? Yes 2 is less than 3. Execute body
<ul>
<li>The computer prints out <code>"i = 2"</code></li>
</ul></li>
<li>Increment <code>i++</code>, i is now 3</li>
<li>Is <code>i &lt; 3</code>? No 3 is not less than 3
<ul>
<li>Don't execute body of loop</li>
</ul></li>
</ul>
<p>Exit loop. Print <code>"After loop, i = 3"</code></p>
<h3>Condensing Syntax</h3>
<p>You can also do the declaration in the initialization statement</p>
<pre><code class="language-java">for (int i = 0; i &lt; 3; i++) {
System.out.println("i = " + i);
}</code></pre>
<p>This now runs like above without the <code>"After loop, i = 3"</code> print. You cannot access the variable <code>i</code> outside the for loop since in this example, it belongs to the for loop's scope.</p>
<h2>Logic Expressions</h2>
<h3>And Statements</h3>
<p>With the AND operator <code>&amp;&amp;</code> both the left and right side needs to be true for the expression to be true.</p>
<pre><code class="language-java">true &amp;&amp; true // true
true &amp;&amp; false // false
false &amp;&amp; true // false
false &amp;&amp; false // false</code></pre>
<h3>Or Statements</h3>
<p>With the OR operator <code>||</code> either the left or right side needs to be true for the expression to be true.</p>
<pre><code class="language-java">true || true // true
true || false // true
false || true // true
false || false // false</code></pre>
<h3>Examples</h3>
<p><strong>Example</strong>: Print out the number <code>n</code> if it is between 10 and 20 (inclusive)</p>
<pre><code class="language-java">if (n &gt;= 10 &amp;&amp; n &lt;= 20) {
System.out.println(n);
}</code></pre>
<p><strong>Example</strong>: Print out the <code>age</code> if it is not of young adult age. Young adult range is from 18 to 39 (inclusive)</p>
<pre><code class="language-java">if (!(age &gt;= 18 &amp;&amp; age &lt;= 39)) {
System.out.println(age);
}</code></pre>
<p>Or you can use De Morgan's Law (for the curious)</p>
<pre><code class="language-java">if (age &lt; 18 || age &gt; 39) {
System.out.println(age);
}</code></pre>
<h2>For Loops (Cont.)</h2>
<h3>Backwards counting</h3>
<p>You can use the loop to count backwards</p>
<pre><code class="language-java">for (int i = 10; i &gt; -1; i--) {
System.out.println(i);
}</code></pre>
<p>This prints the following</p>
<pre><code class="language-java">10
9
8
7
6
5
4
3
2
0</code></pre>
<h3>Rows-Columns</h3>
<p>You can make rows and columns of asterisks</p>
<pre><code class="language-java">for (int j = 0; j &lt; someNumber; j++) { // Corresponds to rows
for (int i = 0; i &lt; someNumber2; i++) { // Corresponds to columns
System.out.print("*");
}
System.out.println(""); // Goes to the next row
}</code></pre>
<p>If <code>someNumber</code> equals <code>someNumber2</code>, then we have the same amount of rows as columns.</p>
<p>Let <code>someNumber</code> equal to 2 and <code>someNumber2</code> equal to 2</p>
<p>Output:</p>
<pre><code>**
**</code></pre>
<h3>Right Triangles</h3>
<p>You can make a right triangle of Tilda with the following code</p>
<pre><code class="language-java">for (int i = 1; i &lt;= num; i++) { // Corresponds to the row
for (int j = 0; j &lt; i; j++) { // Corresponds to the column and stops at the current row number
System.out.print("~");
}
System.out.println(""); // Moves to next row
}</code></pre>
<h5>What are for-loops used for? <em>Reusing code</em></h5>
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