使用 for loop,break,and continue 查找字母 "x" 在句子中出现的次数

Question

多年未编码后，我刚刚回到 JAVASCRIPT 并尝试刷新我对如何使用 "FOR"、"BREAK"、"CONTINUE" 循环的记忆。

我想要实现的是找到一个特定字母在句子中出现了多少次 console.log 它，所以基本上

1. 我创建了一个包含我的句子

的新变量“mywords”

var mywords="this is the for loop wiTh break and continue.".toLowerCase();

2. 比变量“myletter” 比包含要查找的字母的值

var myletter ='t';

3. 和一个变量“howmanytime” 计算字母在句子中出现的次数

var howmanytime = 0;

4. 接下来我创建了一个for循环来计算句子的长度，不断循环并将+ 1添加到“howmanytime " 使用 i++ 直到 i 等于句子长度

for (var i=0; i <= mywords.length;i++){
if (mywords[i]===myletter){
    howmanytime ++;
}

*所以现在 howmanytime 的值是 4，我知道字母 t 在句子中出现了 4 次

5. 接下来，我在我的 for 循环中创建了 if 语句，检查该字母是否出现超过 4 次或更少，以防它出现超过 4 次显示在 console.log 句子中出现的字母数 + "more than 3" if so than break 如果小于则循环4比只显示"less than 3"

if (howmanytime >= 4) {
console.log('more than 3');
console.log('the letter ' + myletter.toUpperCase() + ' appearing ' + howmanytime + ' times in the senetnce');    
break;    

}else if (howmanytime <=4 ){    

console.log('less than 3');
continue;
 }

现在的问题： 我无法弄清楚为什么当一个字母少于 4 次时会显示 "e" 在控制台日志中 "less than 3 times" 没有我想要的任何其他文本

但是当它超过 4 次时让我们回到字母 "t" 它正在显示 "more than 3" 和 "less than 3"

为什么 "less than 3" 也出现了？

我的完整代码

var mywords = "this is the for loop wiTh break and continue.".toLowerCase();

var howmanytime = 0;
var myletter = 'e';

for (var i = 0; i <= mywords.length; i++) {
  if (mywords[i] === myletter) {
    howmanytime++;
  }

  if (howmanytime >= 4) {
    console.log('more than 3');
    console.log('the letter ' + myletter.toUpperCase() + ' appearing ' + howmanytime + ' times in the senetnce');
    break;
  } else if (howmanytime <= 4) {
    console.log('less than 3');
    continue;
  }
}

Answer 1

这是一个稍微有用的代码版本，它指示正在发生的事情

var mywords = "this is the for loop wiTh break and continue.".toLowerCase();

var howmanytime = 0;
var myletter = 't';

for (var i = 0; i <= mywords.length; i++) {
  if (mywords[i] === myletter) {
    howmanytime++;
    console.log('Found ' + howmanytime + ' times the letter ' + myletter);
  }

  if (howmanytime >= 4) {
    console.log('more than 3');
    console.log('the letter ' + myletter.toUpperCase() + ' appearing ' + howmanytime + ' times in the sentence');
    break;
  }
}

/* NOTE! Outside of the loop */
if (howmanytime < 4) {
    console.log('less than 3');
}

Answer 2

I can't figurate out why when a letter is less than 4 times for example "e" it's displayed in a console log "less than 3 times" without any other text which is what I want

因为您在 if 块 if (howmanytime >= 4) 中显示的其他文本。对于字母 "e"，它永远不会为真，因此不会记录其他文本。

but when it's more than 4 times lets go back to letter "t" it's displaying "more than 3" and "less than 3" why the "less than 3" is appearing as well?

因为最初的 howmanytime 是 0 随着字母 "t" 出现在字符串中而继续增加。它在循环开始时不是 4 或超过 4。

如果你想在最后显示全部，只需将 if 语句移出循环体。

var mywords = "this is the for loop wiTh break and continue.".toLowerCase();

var howmanytime = 0;
var myletter = 'e';

for (var i = 0; i <= mywords.length; i++) {
  if (mywords[i] === myletter) {
    howmanytime++;
    if(howmanytime >= 4) break;
  }  
}

if (howmanytime >= 4) {
    console.log('more than 3');
  }
  
else if (howmanytime <= 4) {
    console.log('less than 3');
  }
console.log('the letter ' + myletter.toUpperCase() + ' appearing ' + howmanytime + ' times in the senetnce');

Answer 3

howmanytime >= 4 将为集合 [4,5,6,7,8,9...]

true

howmanytime <= 4 将为集合 [4,3,2,1,0,-1...]

true

如果你想看看 howmanytime 是否至少 3 你应该做 howmanytime >= 3 而 else 应该是 howmanytime < 3

请查看下面的交互示例：

function checkLetter(mywords, myletter) {
  var howmanytime = 0;
  for (var i = 0; i <= mywords.length; i++) {
    if (mywords[i] === myletter) {
      howmanytime++;
    }

    if (howmanytime >= 3) {
      break;
    } else if (howmanytime < 3) {
      continue;
    }
  }

  if (howmanytime >= 3) {
    console.log('more than 3');
    console.log('the letter ' + myletter.toUpperCase() + ' appearing ' + howmanytime + ' times in the senetnce');
  } else {
    console.log('less than 3');
  }
}

var mywords = "this is the for loop wiTh break and continue.".toLowerCase();

document.querySelectorAll("button").forEach(function(dom) {
  dom.addEventListener("click", function() {
    console.clear();
    checkLetter(mywords, dom.getAttribute("letter"));
  });
});

<button letter="a">Check 'A'</button>
<button letter="e">Check 'E'</button>
<button letter="t">Check 'T'</button>

一些注意事项：

JavaScript 的命名约定是 camel-case，这意味着您应该将变量命名为 myWords 而不是 mywords。
else if (howmanytime < 3) 部分是不必要的。在这种情况下，一个简单的 else 可以完成相同的任务。

Answer 4

您可以交换条件并省略 else 部分，方法是对第一部分使用 continue，对第二个条件使用 break。

var mywords = "this is the for loop wiTh break and continueeee.".toLowerCase(),
    howmanytime = 0,
    myletter = 'e',
    i;

for (i = 0; i < mywords.length; i++) { // go only until smaller length,
    if (mywords[i] === myletter) {     // the last is length - 1
        howmanytime++;
        if (howmanytime < 3) {
            console.log('less than 3');
            continue;
        }
        if (howmanytime >= 4) {
            console.log('more than 3');
            console.log('the letter ' + myletter.toUpperCase() + ' appearing ' + howmanytime + ' times in the sentence');
            break;
        } 
    }
}

使用 for loop,break,and continue 查找字母 "x" 在句子中出现的次数

Finding how Many time the letter "x" is appear in the sentence using for loop,break,and continue

javascript

for-loop

continue

break