Logic Tests Series (3) - SUBT 逻辑测试系列之三 - SUBT

justyy (82)in #cn • 7 years ago (edited)

@justyy 's series of Logits Tests:

We have implemented the DECR function in last series using the only four keywords in this tiny programming language. This post, you will need to implement the SUBT function which takes two parameters and subtract one from the other i.e. X-=Y

In C++, you can probably implement this using a LOOP.

void subt(unsigned int &x, unsigned int y) {
  for (int i = 0; i < y; i ++) {
     x --;
  }
}

We take one from X variable Y times and the variable X is a reference variable in C++. If we translate this into this language, here it comes:

SUBT(X, Y) {
   LOOP(Y) {
       DECR(X)  // DECR has been implemented, so we can use it.
  }
}

As you see, complex functions are built upon simple instructions namely ASGN, LOOP, INCR and ZERO. We are going to explore more in the next coming series, please be patient!

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@justyy 的逻辑测试系列:

上次添加了 DECR 函数来把一个变量减一，我们这次来定义一个 SUBT 函数来实现把减法运算，也就是 X-=Y

如果我们用 C++ 来实现，大概是这样的:

void subt(unsigned int &x, unsigned int y) {
  for (int i = 0; i < y; i ++) {
     x --;
  }
}

这里 x 变量是引用，也就是直接在函数里能修改其值，退出函数后x能有变化。我们翻译成这门语言是：

SUBT(X, Y) {
   LOOP(Y) {
       DECR(X)  // DECR 在上期已经定义过了，这里拿来一用。
  }
}

复杂的函数是一点一点建立起来的，虽然这门语言只有 INCR, ZERO, ASGN, LOOP 这四个关键字，但是我们可以通过组合实现最基本的功能，进而完成更复杂的功能，让我们拭目以待。

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// Later, it may be reposted to my blogs: justyy.com, helloacm.com and codingforspeed.com 稍后同步到我的中文博客和英文计算机博客。

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