# BcMath\Number::mul

(PHP 8 >= 8.4.0)

BcMath\Number::mul — Multiplies an arbitrary precision number

### 说明

public BcMath\Number::mul(BcMath\Number|string|int `$num`, ?int `$scale` = `null`): BcMath\Number

Multiplies $this by `num`.

### 参数

`num`
  The multiplier.
`scale`
  BcMath\Number::scale explicitly specified for calculation results. If `null`, the BcMath\Number::scale of the calculation result will be set automatically.

### 返回值

Returns the result of multiplication as a new BcMath\Number object.

When the BcMath\Number::scale of the result object is automatically set, the sum of the BcMath\Number::scales of the two values used for multiplication is used.

That is, if the BcMath\Number::scales of two values are `2` and `5` respectively, the BcMath\Number::scale of the result will be `7`.

### 错误／异常

This method throws a ValueError in the following cases:

- `num` is string and not a well-formed BCMath numeric string
- `scale` is outside the valid range
- BcMath\Number::scale of the result object is outside the valid range

### 示例

示例 #1 BcMath\Number::mul() example when `scale` is not specified

`<?php
$number = new BcMath\Number('1.234');
$ret1 = $number->mul(new BcMath\Number('2.3456'));
$ret2 = $number->mul('-3.4');
$ret3 = $number->mul(7);
var_dump($number, $ret1, $ret2, $ret3);
?>`

以上示例会输出：

    object(BcMath\Number)#1 (2) {
      ["value"]=>
      string(5) "1.234"
      ["scale"]=>
      int(3)
    }
    object(BcMath\Number)#3 (2) {
      ["value"]=>
      string(9) "2.8944704"
      ["scale"]=>
      int(7)
    }
    object(BcMath\Number)#2 (2) {
      ["value"]=>
      string(7) "-4.1956"
      ["scale"]=>
      int(4)
    }
    object(BcMath\Number)#4 (2) {
      ["value"]=>
      string(5) "8.638"
      ["scale"]=>
      int(3)
    }

示例 #2 BcMath\Number::mul() example of explicitly specifying `scale`

`<?php
$number = new BcMath\Number('1.234');
$ret1 = $number->mul(new BcMath\Number('2.3456'), 1);
$ret2 = $number->mul('-3.4', 10);
$ret3 = $number->mul(7, 0);
var_dump($number, $ret1, $ret2, $ret3);
?>`

以上示例会输出：

    object(BcMath\Number)#1 (2) {
      ["value"]=>
      string(5) "1.234"
      ["scale"]=>
      int(3)
    }
    object(BcMath\Number)#3 (2) {
      ["value"]=>
      string(3) "2.8"
      ["scale"]=>
      int(1)
    }
    object(BcMath\Number)#2 (2) {
      ["value"]=>
      string(13) "-4.1956000000"
      ["scale"]=>
      int(10)
    }
    object(BcMath\Number)#4 (2) {
      ["value"]=>
      string(1) "8"
      ["scale"]=>
      int(0)
    }

### 参见

- bcmul() - 两个任意精度数字乘法计算
- BcMath\Number::div() - Divides by an arbitrary precision number
- BcMath\Number::pow() - Raises an arbitrary precision number
- BcMath\Number::powmod() - Raises an arbitrary precision number, reduced by a specified modulus

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