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    <ul> <li><p><code>while ( condition ) { LoopBody() }</code><br/>executes <code>LoopBody()</code> zero or more times.</p> <p><code>condition</code> is checked <strong>prior</strong> to executing the loop body: so long as <code>condition</code> is <code>true</code>, the loop body is executed. </p></li> <li><p><code>do { LoopBody() } while ( condition )</code><br/>executes <code>LoopBody()</code> one or more times.</p> <p><code>condition</code> is checked <strong>after</strong> executing the loop body. It is the <strong>exact</strong> equivalent of</p> <pre><code>LoopBody() ; while ( condition ) { LoopBody() ; } </code></pre></li> </ul> <p>One should note that if the body of the loop never changes the condition, the loop while never terminate.</p> <p>Edited to note: <code>for</code> is for all intents and purposes a while loop. Your <code>for</code> loop:</p> <pre><code>for (int i = int.Parse(textBox3.Text); i &lt;= j; i++) { LoopBody() ; } </code></pre> <p>is roughly equivalent to:</p> <pre><code>int i = int.Parse(textBox3.Text) ; while ( i &lt;= j ) { LoopBody() ; i++ ; } </code></pre> <p>The "roughly bit is because the loop indexer is scoped to the <code>for</code> loop as if it were written</p> <p>{ // introduces a scope int i = int.Parse(textBox3.Text) ; while ( i &lt;= j ) { LoopBody() ; i++ ; } } // end of scope</p> <p>And that's not quite the same as the for loop, because were you to introduce a new <code>i</code> in the method, you'd get a compiler whine about duplicate variable names. A <code>for</code>-loop doesn't have that problem. The compiler is perfectly happy with something like this:</p> <pre><code>if ( condition-A ) { for ( int i = 0 ; i &lt; 10 ; ++i ) { DoSomethingUseful(i) ; } } else { for ( int i = 0 ; i &lt; 10 ; ++i ) { DoSomethingElseUseful(i) ; } } </code></pre> <p>whereas something like this would cause the compiler to whine:</p> <pre><code>if ( condition-A ) { int i = 0 ; while ( i &lt; 10 ) { DoSomethingUseful(i) ; ++i ; } } else { int i = 0 ; while ( i &lt; 10 ) { DoSomethingElseUseful(i) ; ++i ; } } </code></pre> <p>Hope this helps.</p> <p>Refactoring your code to use a <code>while</code> loop would give you something like this:</p> <pre><code>private void calculate_Click(object sender, EventArgs e) { int i = int.Parse( textBox3.Text ) ; int j = int.Parse( textBox2.Text ) ; int multiplyBy = int.Parse( multiplier.Text ) ; while ( i &lt;= j ) { int answer = multiplyBy * i ; string value = string.Format( "{0} times {1} = {2}" , i , mulitplyBy , answer ) ; listBox1.Items.Add( value ) ; ++i ; } return ; } </code></pre>
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    1. USNicholas Carey
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    1. CO"if the body of the loop never changes the condition, the loop while never terminate" --- it's not entirely correct. Not only the body can/must change the condition, but the condition can change naturally. Like time based comparisons or comparisons with random numbers
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    2. COI believe this answer is enough to get @user2856358 started applying `do/while `and `while` in the code on his own.
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