javascript - 在 if/else 语句后使用 for 循环

Question

这只是一个简单的乘法程序，使用如果/否则和for 循环。从提示中重新输入一个正数并将其分配给for 循环应该使用会破坏程序。我不知道为什么它是不正确的。 ？也许你可以告诉我使用 如果/ 否则和 for 循环。非常感谢任何帮助。

//Array variable and counter variable

var multi = new Array();

var Counter;

//Enter a number between 1 and 12 and hold in num variable

num = prompt("Enter a number between 1 and 12");

//Check if number is less than zero
//Reenter positive number

if (num < 0) {
    var num = prompt("Enter a number greater than zero");
} 
else {
    //Number entered by user multiplied by counter value
    for (Counter = 1; Counter <= 12; Counter++) {
        multi[Counter] = num * Counter;
    }
    //Loop to display number that is being multiplied each time 
    for (Counter = 1; Counter <= 12; Counter++) {
        document.write(Counter + " x " + num + "  = " + multi[Counter] + '<br/>');
    }
}

Answer 1

这可以在修复代码的同时进行简化。

输入负数导致代码失败的原因是您永远不会命中 else block ，因此永远不会运行其中的预期代码。

正如 melpomene 所建议的那样，do/while 循环在这里可以很好地为您服务。

您也不需要 2 个单独的 for 循环，它们可以压缩为一个。

var num;

do {

  // Enter a number between 1 and 12 and hold in num variable
  // Check if number is not between 1 and 12 and re-enter
  num = prompt("Enter a number between 1 and 12");

} while (num < 1 || num > 12);

// You can define your counter variable within the for loop
for (var counter = 1; counter <= 12; counter++) {

   document.write(counter + ' x ' + num + '  = ' + (num * counter) + '<br/>')

}