问题

以下是翻译后的内容，只包括代码部分：

我想知道是否可以为具有以下条件的计算器输入创建正则表达式，显示从```0```开始：

 - 第一个字符可以是```+```或```-```符号（可选）
 - 如果第一个输入是```.```，它应附加到```0```后面
 - 如果第一个输入是数字，则应占据```0```的位置
 - 数字只能有一个```.```。
 - 在数字之后，可以有运算符```+-/*```。
 - 运算符```/*```可以后跟```+-```。
 - 如果输入是运算符，并且最后一个字符是运算符，则它应占据最后一个字符的位置

允许的输入示例：

``` -0.548*-7+54 ```

错误的输入示例：

```*354*/56-+45```

我可以通过```regex```和```条件语句```的混合来实现这一点（我正在使用React）：

```javascript
const displayPattern = /([+-]?)(\d+)(\.?)(\d*)([*/]?)([+-]?)/g;
const isOperator = /[-+*/]/;
const isNumber = /\d/;
const isSign = /[-+]/;
const lastChar = state.slice(-1);

if (value.includes("AC")) {
  setState("0");
} else if (state.length === 1) {
  if (isNumber.test(value)) {
    if (state === "0") {
      setState(value);
    } else {
      setState(prevVal => prevVal + value);
    }
  } else if (value === ".") {
    setState(prevVal => prevVal + value);
  } else if (isSign.test(value)) {
    setState(value);
  }
} else {
  if (isOperator.test(lastChar) && isOperator.test(value)) {
    if (isSign.test(lastChar)) {
      setState(prevVal => prevVal.slice(0, -1) + value);
    } else {
      !isSign.test(value) && setState(prevVal => prevVal.slice(0, -1) + value);
    }
  }
  setState(
    prevVal =>
      (prevVal + value).match(displayPattern) &&
      (prevVal + value).match(displayPattern).join("")
  );
}

<details>
<summary>英文:</summary>
I was wondering if it is possible to make a regex for a calculator input with these conditions, the display starts with a ```0```:
- the fist char can be an ```+``` or ```-``` sign (optional)
- if the first input is a ```.``` it should be appended to the ```0```
- if the first input is a number it should take the place of the ```0```
- the number can have only one ```.```
- after a number I can have an operator ```+-/*```
- the operator ```/*``` can be followed by an ```+-```
- if the input is an operator and the last char is a operator it should take the place of the last char
Allowed input example:
``` -0.548*-7+54 ```
Wrong input example:
```*354*/56-+45```
I could do that with a mix of ```regex``` and ```conditionals``` (I&#39;m using React):

const displayPattern = /([+-]?)(\d+)(.?)(\d*)([/]?)([+-]?)/g;
const isOperator = /[-+/]/;
const isNumber = /\d/;
const isSign = /[-+]/;
const lastChar = state.slice(-1);

if (value.includes("AC")) {
setState("0");
} else if (state.length === 1) {
if (isNumber.test(value)) {
if (state === "0") {
setState(value);
} else {
setState(preVal => preVal + value);
}
} else if (value === ".") {
setState(preVal => preVal + value);
} else if (isSign.test(value)) {
setState(value);
}
} else {
if (isOperator.test(lastChar) && isOperator.test(value)) {
if (isSign.test(lastChar)) {
setState(prevVal => prevVal.slice(0, -1) + value);
} else {
!isSign.test(value) && setState(prevVal => prevVal.slice(0, -1) + value);
}
}
setState(
preVal =>
(preVal + value).match(displayPattern) &&
(preVal + value).match(displayPattern).join("")
);
}

</details>
# 答案1
**得分**: 2
以下是翻译好的部分：
像这样的代码可以工作：
^[+-]?\d*\.*\d+(?:[+*\/-][+-]?\d*\.*\d+)*$
- `^` - 字符串开始锚点
- `[+-]?` - 可选择以正负号开头
- `\d*\.*\d+` - 可选择数字，后跟可选择小数，后跟必须数字。这允许我们考虑整数或小数。
- `(?:[+*\/-][+-]?\d*\.*\d+)*` - 以必须的前置运算符重复可选择的前两个项目的模式
- `$` - 字符串结束锚点
https://regex101.com/r/srl7vj/1
<details>
<summary>英文:</summary>
Something like this would work:
^[+-]?\d*\.*\d+(?:[+*\/-][+-]?\d*\.*\d+)*$
- `^` - start string anchor
- `[+-]?` - start with an optional positive or negative sign
- `\d*\.*\d+` - optional digit, followed by optional decimal, followed by required digit. This allows us to account for whole numbers or decimals.
- `(?:[+*\/-][+-]?\d*\.*\d+)*` - repeating optional pattern of previous two bullet points with a required preceding operator
- `$` - end string anchor
https://regex101.com/r/srl7vj/1
</details>