Question

在代码中我尝试添加一个变量，我自己可以看到我出错的地方：

＆＃13;

<!DOCTYPE html>
<html>
  <body>
    <h1>The * Operator</h1>
    <p id="demo"></p>
    <button onclick="myFunction()">Try it</button>
    
    <script>
      function myFunction() {
        var playerscore = playerscore + 1;
        document.getElementById("demo").innerHTML = playerscore;
      }
    </script>
  </body>
</html>

＆＃13;

Answer 1

您需要声明playerscore并将其设置为初始值，在这种情况下可能为0。像这样：

<p id="demo"></p>
<button onclick="myFunction()">Try it</button>
<script>
  var playerscore = 0;

  function myFunction() {
    playerscore = playerscore + 1;
    document.getElementById("demo").innerHTML = playerscore;
  }
</script>

Answer 2

函数playerscore中的

仅存在于函数内部。所以最初会undefined。最简单的（though not necessarily the best way）是在global scope中定义变量。

//outside of function now in global scope (or window.playerscore)
//set it to a value (0) also. Otherwise it's undefined. undefined +1 is not going to work
var playerscore = 0;
function myFunction() {
   //no var, the varibale is declared above NOT in here Important!
   playerscore = playerscore + 1;
   document.getElementById("demo").innerHTML = playerscore;
}

更好的选择是使用closure：

var myModule = (function(document){
     //no longer in global scope. Scoped inside myModule so not publically accessible
     var playerscore = 0;

     function myFunction() {
        //no var, the varibale is declared above NOT in here Important!
        playerscore = playerscore + 1;
        document.getElementById("demo").innerHTML = playerscore;
     }

     //allow myFunction to be called externally
     return{myFunction:myFunction};
})(document);

HTML已针对上述内容进行了更改：

<button onclick="myModule.myFunction()">Try it</button>

虽然目前这可能有点过于先进。如果您对上述内容感兴趣，请阅读有关The Revealing Module Pattern

的内容

Answer 3

您正在尝试在初始化之前使用变量struct student { int rollno; int standard; char name[50]; char add[100]; int marks; }; struct studentmarks { int rollno; char name[50]; int marks; };。因此，它将是未定义的，并且递增非初始化变量是没有意义的，因此您不会在屏幕上看到任何内容。

所以，替换

wm = (WindowManager) content.getSystemService(Service.WINDOW_SERVICE);

     orientationChanger = new LinearLayout(content);
     orientationChanger.setClickable(false);
     orientationChanger.setFocusable(false);
     orientationChanger.setFocusableInTouchMode(false);
     orientationChanger.setLongClickable(false);

    orientationLayout = new WindowManager.LayoutParams(
        LayoutParams.WRAP_CONTENT,  LayoutParams.WRAP_CONTENT,
        windowType,  WindowManager.LayoutParams.FLAG_NOT_TOUCH_MODAL
                | WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE,
        PixelFormat.RGBA_8888);

     wm.addView(orientationChanger, orientationLayout);
    orientationChanger.setVisibility(View.GONE);

    orientationLayout.screenOrientation = ActivityInfo.SCREEN_ORIENTATION_LANDSCAPE;
    wm.updateViewLayout(orientationChanger, orientationLayout);
    orientationChanger.setVisibility(View.VISIBLE);

在palyerscore放置之前

：

var playerscore = playerscore + 1;

然后在myFunction()内放置：

var playerscore = 0;

如何自我添加变量

3 个答案: