What's going on with the initial value being skipped in a Python loop?

Analysis of the reason why Python loops skip initial value

In Python programming, the initial value of a loop statement is sometimes accidentally skipped, which is often confusing. This article will analyze a typical case and explain its root cause.

Problem description

Consider the following Python code snippet:

 i = 10
While i <p> This code is intended to print all numbers between 10 and 100 that can be divisible by 5. However, the initial value of 10 is missing from the running result. Why does this happen?</p><h4 id="Problem-analysis"> Problem analysis</h4><p> The key lies in the position of the <code>i = 1</code> statement. It is before the <code>if</code> statement. This means that at the beginning of each cycle, the value of <code>i</code> will be incremented by 1 first, and then the conditional judgment will be made.</p><p> First loop:</p><ol>
<li> The value of <code>i</code> is 10.</li>
<li> <code>i = 1</code> executes, <code>i</code> becomes 11.</li>
<li> <code>if i % 5 != 0:</code> The condition is true (11 cannot be divisible by 5), the <code>continue</code> statement is executed, and <code>print(i)</code> is skipped.</li>
</ol><p> Therefore, the initial value 10 never enters the judgment condition of the <code>if</code> statement, and it is not printed.</p><h4 id="Solution"> Solution</h4><p> In order to include the initial value 10, you can adjust the code structure and place the auto-increment statement after the <code>if</code> statement:</p><pre class="brush:php;toolbar:false"> i = 10
While i <p> Alternatively, print the initial value before the loop starts:</p><pre class="brush:php;toolbar:false"> i = 10
print(i) # Print initial value while i <p> Both modifications ensure that the initial value 10 is printed correctly.</p><h4 id="in-conclusion"> in conclusion</h4><p> The phenomenon that the initial value in a loop statement is skipped usually because the code logic causes the initial value to be modified before the conditional judgment. Carefully checking the order of modification of variables in the loop body is the key to avoiding such problems. Correct code structure and variable processing methods can ensure the expected behavior of the program.</p>

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