Why does dividing 8 by -3 in PHP result in 0?

Why is PHP8%-3 equal to 0?

In PHP programming, sometimes we encounter some strange and confusing problems. A particularly interesting question is, why does the expression 8%-3 in PHP equal 0?

To answer this question, first we need to understand the modular operation (remainder operation) in PHP. Modulo arithmetic is a mathematical operation used to calculate the remainder after dividing one number by another. In PHP, the percent sign (%) is used to represent modular arithmetic.

In mathematics, when one number is divided by another number and the remainder is 0, we say that the two numbers are divisible. In other words, if one number is divisible by another number, the result of the modulo operation between them will be 0.

Next, let’s take a look at why the result of PHP8%-3 is 0.

First of all, we need to understand PHP's processing rules for modular operations. Under normal circumstances, the result of modulo arithmetic should be a non-negative integer. But in PHP, the sign of the remainder is the same as the sign of the dividend. That is, if the dividend is positive, the remainder is also positive; if the dividend is negative, the remainder is also negative.

In this example, 8 is the dividend and -3 is the divisor. Since 8 is a positive number, the remainder should also be positive. But according to PHP's rules, the sign of the remainder is the same as the sign of the dividend, so the remainder is negative. This is why the result of 8%-3 is -1 instead of the normal 1.

Then the question is, why is the result of 8%-3 not -1, but 0?

In fact, this is because there is an exception to the modular operation in PHP. When the absolute value of the dividend is less than the absolute value of the divisor, the result of the modulo operation is equal to the dividend. In other words, the result of 8%-3 is equal to 8. This is why the result of 8%-3 is 0.

This situation can also be verified through mathematical calculations. We know that -3 divides 8 once, with a remainder of 2. According to PHP rules, the sign of the remainder is the same as the sign of the dividend, so the remainder is -2. But the special rules in PHP change the remainder to 0, so the result becomes 8%3=0.

Although this special rule is not mathematically strict, it helps us solve some special cases in PHP. In actual programming, we may encounter some problems that need to consider this special situation. By understanding this rule, we can better handle these problems and avoid errors.

To summarize, the reason why PHP8%-3 is 0 is because PHP has a special rule when dealing with modular operations. When the absolute value of the dividend is less than the absolute value of the divisor, the result of the modular operation is equal to the dividend. This special rule helps us solve some special cases, but is not mathematically rigorous. Understanding this rule can help us better handle these special situations and avoid errors.

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