result
calc('0.23*-0.03+(4*0.2)')
=>0.7931
the code
//加|减|乘|除 浮点运算
const floatMulti = (a, b) => {
let m = 0, s1 = a.toString(), s2 = b.toString(), s1l = s1.split('.')[1], s2l = s2.split('.')[1]
m = (s1l ? s1l.length : 0) + (s2l ? s2l.length : 0)
return Number(s1.replace('.', '')) * Number(s2.replace('.', '')) / Math.pow(10, m)
}
const floatSub = (a, b) => {
let m = 0, s1 = a.toString(), s2 = b.toString(), s1l = s1.split('.')[1], s2l = s2.split('.')[1]
m = Math.max((s1l ? s1l.length : 0) ,(s2l ? s2l.length : 0))
return(Number(s1)*Math.pow(10, m) - Number(s2)*Math.pow(10, m)) / Math.pow(10, m)
}
const floatAdd = (a, b) => {
let m = 0, s1 = a.toString(), s2 = b.toString(), s1l = s1.split('.')[1], s2l = s2.split('.')[1]
m = Math.max((s1l ? s1l.length : 0) ,(s2l ? s2l.length : 0))
return (Number(s1)*Math.pow(10, m) + Number(s2)*Math.pow(10, m)) / Math.pow(10, m)
}
const floatDev = (a, b) => {
let m = 0, s1 = a.toString(), s2 = b.toString(), s1l = s1.split('.')[1], s2l = s2.split('.')[1]
m = (s1l ? s1l.length : 0) + (s2l ? s2l.length : 0)
return (Number(s1.replace('.', '')) / Number(s2.replace('.', ''))) / Math.pow(10, m)
}
/*
* 浮点运算式
* */
export const calc = (() => {
//一般的算数表达式即为中缀表达式
// let str = "1+((2 + 3 ) * 4 ) - 5 ";
//运算符权重
const sdw = {
'+': 1, '-': 1, '*': 2, '/': 2 };
//循环安全数
let saveCircle = 137;
/**
*判断是 运算符|操作数|括号
* 【-】字符前面有任何其他运算符则本身被当作数字一部分
*@return 1:操作数 2:括号 0:运算符
*/
const typeChk = (d) => /^-*[\.\d]+$/.test(d) ? 1 : (/[\(\)]/.test(d) ? 2 : 0)
/*
* 操作符操作方法
* */
const handle = {
'+': floatAdd, '-': floatSub, '*': floatMulti, '/': floatDev }
/**
* 处理输入
* 1) 替换中英括号
* 2) 去除空格
* 3) 小数点前后非数字,则去除
* 3) 小数点之前为空,后面为数字则默认前面添加0
* 4) 返回字符分割
*/
const dealStr = (str) => str
//替换左右括号
.replace(/(/, '(')
.replace(/)/, ')')
//替换空字符
.replace(/[^\d\.\(\)\+\*\/-]/g, '')
//替换-
// .replace(/(\d)-/g,'$1+-')
// .replace(/--/g,'+')
// .replace(/-\(/g,'-1*(')
// .replace(/-/g,'+-1*')
.match(/(((?<=[^\d])-[\.\d]+)+)|(^-[\.\d]+)|([\d\.]+)|([\(\)\+\*\/-])/g)
//中缀表达式转前缀表达式并计算
return (str) => {
let operand = [];//操作数栈
let operator = [];//操作符栈
//去空格(主要是避免数字被空格拆分),分割成数组
let arr = dealStr(str);
// log(arr)
//按照规则入栈
let type;
for (let i = arr.length - 1, curr; (curr = arr[i]) != null; i--) {
type = typeChk(curr);
if (type === 1) {
operand.push(+curr)
} else if (type === 0) {
let si = 0, stackTop;
while (true && si++ < saveCircle) {
stackTop = operator[operator.length - 1];
if (stackTop == null || stackTop === ')') {
operator.push(curr);
break;
} else if (sdw[curr] >= sdw[stackTop]) {
operator.push(curr);
break;
} else {
operand.push(operator.pop())
}
}
} else {
if (curr === ')') {
operator.push(curr)
}else{
let s, si = 0;
while (s !== ')' && si++ < saveCircle) {
s = operator.pop();
if (s === ')') break
operand.push(s)
}
}
}
}
//将操作符栈中剩下的弹出压入操作数栈
// operand = [...operand, ...operator.reverse()];// num => ["5", "4", "3", "2", "+", "×", "1", "+", "-"]
//"1+((2 + 3 ) × 4 ) - 5 "
let prevStack = [...operator, ...operand.reverse()];// ["-", "+", "1", "×", "+", "2", "3", "4", "5"]
//计算
let resultStack = [], left, right;
for (let i = prevStack.length - 1, curr; (curr = prevStack[i]) != null; i--) {
if (typeChk(curr)) {
//是操作数
resultStack.push(curr)
} else {
//是操作符
left = resultStack.pop();
right = resultStack.pop();
// console.log(left,right,curr)
resultStack.push(handle[curr](left, right))
}
}
// log(prevStack);
//log(resultStack);
return resultStack.length != 1 ? '表达式有误' : resultStack[0]
}
})()