JavaScript Prime编号查询

Question

这是我的代码：

  var num = parseInt(105);
  // debugger
  if (num < 1) {
    console.log("=> 0 or minus value is not a prime number", num);


  } else if (num == 2) {
    console.log("=> 2 is a prime number", num);


  } else if (num > 2) {

    for (i = 2; i < num; i++) {
      if (num % i == 0) {
        console.log("this is a not prime number as it is devided by zero");
        break


      } else {
        console.log("this is a prime number")

      }
    }
  }

在此代码中，为什么当我将任何奇数数字放置在我已经磨损的任何奇数时，请显示输出，以停止循环中断。

Answer 1

如果该数字不能由特定的i排除，那么您的其他条件将被执行。更改num为5您会看到这是一个素数打印几次。

您可以创建一个函数（如下所示），在其中我们首先检查所有i s，然后打印这是一个Prime Number。

function isPrime(num) {
  if (num < 1) {
    console.log("=> 0 or negative values are not prime numbers", num);
  } else if (num === 2) {
    console.log("=> 2 is a prime number", num);
  } else if (num > 2) {
    for (let i = 2; i < num; i++) {
      if (num % i === 0) {
        console.log(`this is a not prime number as it is divisible by ${i}`);
        return;
      }
    }
  }
  console.log("this is a prime number");
}

isPrime(105);

或者，您可以将结果存储在变量中，并且在循环打印的末尾，如果未设置该变量，则是素数。

const num = 105;
if (num < 1) {
  console.log("=> 0 or negative values are not prime numbers", num);
} else if (num === 2) {
  console.log("=> 2 is a prime number", num);
} else if (num > 2) {
  let isPrime;
  for (let i = 2; i < num; i++) {
    if (num % i === 0) {
      console.log(`this is a not prime number as it is divisible by ${i}`);
      isPrime = false;
      break;
    }
  }
  if (isPrime !== false) {
    console.log("this is a prime number");
  }
}