提问人：HuMaNBeinG69420 提问时间：4/15/2023 更新时间：4/16/2023 访问量：66
整数“x”的起始值应该是多少？
The start value of integer "x" should be how many?
问：
这是一个简单的函数：
function sequence(a,b,c,d){
var x = 0;
var y = 0;
for(var i = a; i<=b; i++){
y = eval(c);
x = eval(d);
}
return x;
}
A&B 必须是整数，C&D 必须是字符串
此代码获取 1 到 5 的总和：
sequence(1,5,"i","x+y")
结果：
15
此代码获取 1 到 5 的乘积：
sequence(1,5,"i","x*y")
结果：
0
问题出在“”处，“”的值应该是多少？var x = 0;x
sequence(1,5,"i","x+y") >>> 15
sequence(1,5,"i","x*y") >>> 0
sequence(1,5,"i","x-y") >>> -15
sequence(1,5,"i","x/y") >>> 0
sequence(1,5,"i","x**y") >>> 0
sequence(1,5,"i","x%y") >>> 0
答：
0赞
tatactic
4/16/2023
#1
我希望当你写这个块时，>>>后面的数字不是预期的结果，否则我不明白你的问题！
sequence(1,5,"i","x+y") >>> 15
sequence(1,5,"i","x*y") >>> 0
sequence(1,5,"i","x-y") >>> -15
sequence(1,5,"i","x/y") >>> 0
sequence(1,5,"i","x**y") >>> 0
sequence(1,5,"i","x%y") >>> 0
请注意，% 代表模而不是百分比，我不知道你对结果的期望是什么！
我不明白参数中的“i”代表什么。 使用某些值时，** 运算符存在问题。 我在下面的片段中评论了这一点。
警告：从字符串执行 JavaScript 存在巨大的安全风险。
当您使用 eval（） 时，不良行为者运行任意代码太容易了。
请参见 ： https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/eval
这是一个仅在 a<b 时有效的片段，我将在下面添加另一个如果 a>b 也有效的片段。
"use strict";
function operationFromAtoB(a,b,c){
// You don't have to declare x here
var y = "";
for (var i = a; i <= b; i++) {
if(i != b){
y += (i.toString() + c );
}else{
y += (i.toString())
}
}
var result = y + " = " + eval(y);
return result;
}
console.log(operationFromAtoB(1,5,"+"));
console.log(operationFromAtoB(1,5,"*"));
console.log(operationFromAtoB(1,5,"-"));
console.log(operationFromAtoB(1,5,"/"));
// Next line throws NaN or Infinity if out of range
console.log(operationFromAtoB(2,4,"**"));
// 1**2**3**4**5 = NaN
// 2**3**4**5 = Infinity
// 2**3**4 = 2.4178516392292583e+24
console.log(operationFromAtoB(1,5,"%"));这里有一个片段，如果 a<b 和 a>b 有效：
function operationFromAtoB(a,b,c){
var result = "";
var y = "";
if(a<b){
for (var i = a; i <= b; i++) {
if(i != b){
y += (i.toString() + c );
}else{
y += (i.toString())
}
}
}else{
for (var j = a; j >= b; j--) {
if(j != b){
y += (j.toString() + c );
}else{
y += (j.toString())
}
}
}
result = y + " = " + eval(y);
return result;
}
console.log("a<b !!!")
console.log(operationFromAtoB(1,5,"+"));
console.log(operationFromAtoB(1,5,"*"));
console.log(operationFromAtoB(1,5,"-"));
console.log(operationFromAtoB(1,5,"/"));
console.log("a>b !!!")
console.log(operationFromAtoB(5,1,"+"));
console.log(operationFromAtoB(5,1,"*"));
console.log(operationFromAtoB(5,1,"-"));
console.log(operationFromAtoB(5,1,"/"));
评论
reduce。必须传入初始值，因为没有一个适合所有用途的单个初始值。sequence(1,5,"i","x*y")