The difference between ceil() and round() and its application scenarios

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In PHP, you often encounter scenarios that need to be "rounded" when processing floating point numbers. At this time, ceil() and round() are the two most common functions. Although they all involve floating-point numbers to integer conversions, their behavior is very different from the applicable scenarios. This article will introduce the differences between these two functions in depth and analyze their suitable usage scenarios.

1. ceil() function: round up

ceil() is the abbreviation of English ceiling (ceiling). As the name suggests, its function is to round a number upwards. Regardless of the fractional part, as long as it is not an integer, ceil() will add it and return the nearest larger integer.

Example of usage:

<code> echo ceil(4.2); // Output 5 echo ceil(-4.2); // Output -4 </code>

As you can see, ceil() is "adding one" for positive numbers, while for negative numbers, it is rounded in the direction of "zero", that is, "get smaller".

Application scenarios:

1. Calculate the total number of pages in paging logic <br> When you know the total number of records and the number of pieces displayed per page, you usually need to use ceil() to calculate the total number of pages.

   <code> $total_items = 105; $items_per_page = 10; $total_pages = ceil($total_items / $items_per_page); // The result is 11 </code>

2. Prices are rounded up to avoid losses <br> For example, when setting the minimum payment amount on an e-commerce website, it may be necessary to round up the discounted price.

   <code> $discounted_price = 19.2; $final_price = ceil($discounted_price); // The result is 20 </code>

2. round() function: rounding

round() is a function that rounds a number, which can make the number more "human". By default, it rounds the decimal point, or you can specify the number of reserved decimal places through the second parameter.

Example of usage:

<code> echo round(4.2); // Output 4 echo round(4.5); // Output 5 echo round(-4.5); // Output -4 </code>

It is worth noting that PHP's round() uses the "banker rounding method", also known as the "even-number rounding method". When processing decimals at the end of .5 , it will decide whether to abandon or carry according to whether the previous digit is an even number.

<code> echo round(2.5); // Output 2 echo round(3.5); // Output 4 </code>

This avoids errors when a large number of numbers accumulate.

Application scenarios:

1. Display user-friendly values <br> For example, if you want to display product ratings:

   <code> $average_rating = 4.666; echo round($average_rating, 1); // Output 4.7 </code>

2. Numerical balance in financial and accounting systems <br> The banker rounding method can reduce cumulative errors and is therefore often used in financial statistics.

   <code> $price = 2.5; $rounded = round($price); // The result is 2 </code>

3. Chart data processing <br> In the chart, proper rounding can make the data more intuitive and understandable.

   <code> $percentage = (45 / 123) * 100; echo round($percentage, 2); // Output 36.59 </code>

3. Summarize the differences and select suggestions

When choosing to use ceil() or round() , the key is whether you want to ensure that the result is not less than the original value (using ceil() ), or you want the result to be closer to the "average" representation of the original value (using round() ).

For example, you are developing an e-commerce backend management system, using such a paging function in inventory paging display:

<code> function getTotalPages($total_items, $items_per_page) { return ceil($total_items / $items_per_page); } </code>

And if you are dealing with a user satisfaction rating system, you might do this:

<code> function formatRating($rating) { return round($rating, 1); } </code>