Analysis of the reasons why 8%3 equals 0 in PHP

Analysis of the reason why 8%-3 is equal to 0 in PHP

In PHP, if we try to calculate 8%-3, we will get a result of 0 value. This may confuse some developers because in mathematics we expect that the result of evaluating this expression should be 2. However, in PHP, there are some special rules for using the remainder operator (%), which may lead to some unusual results.

First, let us understand the definition of the remainder operator in mathematics. The remainder operator is used to calculate the remainder after dividing one number by another number. In mathematics, this operator is intuitive for positive integers. For example, when calculating the remainder of 8 divided by 3, we get 2. This is because 8 is divisible by 3 twice, leaving a remainder of 2.

However, in PHP, this is not always the case. When the remainder operator is applied to a negative number, the result may be negative, zero, or positive, depending on the signs of the dividend and divisor. Specifically, when the dividend is a positive number and the divisor is a negative number, the calculation rules of the remainder operator are as follows:

1. If the dividend can be divided by the divisor, the result is a negative number.

   • For example, the result of 10 % -3 is -2. Since 10 is divisible by -3, the remainder is -2.

2. If the dividend does not divide the divisor, but the dividend is positive, the result is a positive number.

   • For example, the result of 8 % -3 is 2. Since 8 is not divisible by -3, the remainder is 2.

3. If the dividend does not divide the divisor, but the dividend is negative, the result is a negative number.

   • For example, -8 % -3 results in -2. Since -8 is not divisible by -3, the remainder is -2.

Next, let us analyze why the result of 8%-3 in PHP is 0. According to the above rules, we can know that 8 is a positive number and -3 is a negative number, so the result should be a positive number. However, during the specific calculation process, PHP performs some internal processing.

When calculating 8%-3, PHP will first calculate the largest integer n, so that n times -3 is less than or equal to 8. In this example, n=2 because 2 times -3 equals -6, which is less than or equal to 8. PHP then adds -6 to 8 to get the final result of 2. So, the result is 2 and not 0.

Then why does the result appear to be 0? This is because the remainder operator is also affected by the data type of the dividend. If the dividend is an integer, such as 8, the result is 2. However, if the dividend is a floating point number, such as 8.0, then the result becomes 0.

This is because when the dividend is a floating point number, the calculation inside PHP will convert it to an integer, that is, convert 8.0 to 8, and then perform the calculation according to the rules mentioned earlier. Since 8 does not divide -3, it evaluates to 0.

To sum up, the reason why the result of 8%-3 in PHP is 0 is the impact of PHP's processing rules and data types on negative numbers when calculating the remainder operation. Developers need to pay attention to these rules and data type conversion when writing code to avoid accidental and erroneous calculation results.

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