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第一场,叶小凡赢得非常漂亮。这难免遭到了场外一些大弟子的嫉妒。
“哼,不过才赢了第一场,有什么好神气的。”
“就是,就是啊。不管怎么说,运算符毕竟还是属于比较基础的功夫。我看哪,这个叶小凡只是运气好,正好对这一块比较熟悉罢了。”
第一场结束,16进8,叶小凡成功晋级。第二场的题目,是一道计算题。用JavaScript计算1+2+…+100的值。就在对面还在埋头苦算的时候,叶小凡已经完成了代码。
var sum = 0; for(var i = 1;i < 101;i++){ sum = sum + i; } console.log(sum);
在对手震惊的目光中,叶小凡不慌不忙地开始解释。
“计算1+2+…+100的值,直接一个一个加肯定不行,太慢了,效率太低。因此我想到了用循环。for循环是一个不错的选择。for循环的格式,圆括号里面有三个表达式,当需要进行for循环的时候,就先执行表达式一。也就是var
I = 1。然后执行表达式2,I <
101。表达式2是一个判断条件,和if语句判断有异曲同工之处。当表达式2的结果为布尔类型的true时,就认为符合进入循环的条件,于是接下来就回去执行{}中的内容。”
sum = sum + i;
“在{}里面,就是一个累加的操作,把每一次循环的i加到变量sum上去。当执行完这些代码后,才会去执行表达式3,也就是i++,这句话的意义是让i变量自增一个单位,好让i一直在慢慢变大,直到不符合进入循环的条件为止。”
听到这里,林元青微微点了点头。叶小凡继续说道,“我想这道题的考核要点就是对循环技术的了解程度。其实,这样一道题目也可以用while循环来做。”说着,叶小凡又重新打了一段代码:
var sum = 0; var i = 0; while(i < 101){ sum += i; i++; } console.log(sum);
“while循环和for循环的不同之处,在于while循环只有一个判断的表达式,就好比刚才for循环中的表达式2。至于for循环的表达式3,已经放到{}中去了。表达式一则放到while循环之前去了。就有点类似于这样。”说完,叶小凡又写到,过程没有滞缓,完全行云流水,好像已经烂熟于心似的。
var sum = 0; var i = 0; for(;i < 101;){ sum += i; i++; } console.log(sum);
“嗯,做的不错,这一场,自然还是叶小凡胜了。”林元青宣布比赛结果。
“啥?又赢了,这也太轻松了吧。”叶小凡心中暗惊,也难怪,叶小凡平时都是在叶老的指点下,这种难度的题目实在是有点小儿科了。
叶小凡二连胜,八进四!