Javascript - 查找数字是正数还是负数
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Javascript - Find if number is positive or negative
提问by Pizzaman
I see other solutions to my question but none that help me.
我看到了我的问题的其他解决方案，但没有一个对我有帮助。
I want to create a function to find if a number is positive/negative. The function should take an integer argument and return true if the integer is positive and false if it is negative.
我想创建一个函数来查找数字是否为正/负。该函数应该接受一个整数参数，如果整数为正则返回真，如果为负则返回假。
Also, prompt the user again and again if anything other than a number is entered
此外，如果输入了数字以外的任何内容，请一遍又一遍地提示用户
Here's the code so far
这是到目前为止的代码
When I enter a number, it keeps alerting me it is true or false but won't let me enter another.
How do I control my loop so I can ask until -1is entered? It is not giving me a chance to enter -1
当我输入一个数字时，它会不断提醒我这是真的还是假的，但不会让我输入另一个。我如何控制我的循环，以便我可以询问直到-1输入？它没有给我输入 -1 的机会
function isPositive(num) {
var result;
if (num >= 0) {
result = true;
} else if (num < 0) {
result = false;
}
return result;
}
var num;
num = parseInt(prompt("Enter a number"));
while (num != -1) {
alert(isPositive(num));
if (isNaN(num)) {
alert("No number entered. Try again");
num = parseInt(prompt("Enter a number"));
isPositive(num);
while (num != -1) {
alert(isPositive(num));
}
}
}
回答by Niet the Dark Absol
There's a few things wrong with your code, so here's a rewrite with comments:
你的代码有一些问题，所以这里是一个带有注释的重写：
function isPositive(num) {
// if something is true return true; else return false is redundant.
return num >= 0;
}
// when you want to keep doing something until a condition is met,
// particularly with user input, consider a while(true) loop:
var num;
while (true) {
num = prompt("Enter a number");
// check for null here
if (num === null) {
alert("No number entered. Try again.");
continue; // return to the start of the loop
}
num = parseInt(num, 10); // second argument is NOT optional
if (isNaN(num)) {
alert("Invalid number entered. Try again.");
continue;
}
// once we have a valid result...
break;
}
// the loop will continue forever until the `break` is reached. Once here...
alert(isPositive(num));回答by Praveen Kumar Purushothaman
The number 0is neither positive, nor negative! :P
这个数字0既不是正数也不是负数！:P
function isPositive(num)
{
if(num < 0)
return false;
else
return true;
}
Or a simple way,
或者简单的方法，
function isPositive(num)
{
return (num > 0);
}
回答by treeseal7
Math.sign(number)
which returns either a 1, -1or 0
返回 a 1,-1或0
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Math/sign
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Math/sign
回答by DripDrop
You are testing if it isn't-1. Try this:
您正在测试它是否不是-1。试试这个：
if(num < 0){
...IS NEGATIVE...
}else{
...IS POSITIVE...
}
This checks if it is less than or greater than 0.
这将检查它是小于还是大于 0。
