C编程语言（版本2）中的示例1

C编程语言（版本2）中的示例1-7(Example 1-7 from The C Programming Language(version 2))

我无法理解C语言中给出的示例1.7。 这个例子的主要目的是说明C中函数的使用。本书描述如下程序，“由于C没有像Fortran这样的指数运算符，所以我们通过编写一个函数来说明函数定义的机制功率（m，n）将整数m提升为正幂n，即幂（2,5）的值为32.这个函数不是一个实用的求幂例程，因为它只处理小整数的正幂，但对于插图来说已经足够了。“ 这是下面的C代码块：

#include <stdio.h> int power(int m, int n); /*function prototype */ int main() { /* test power function */ int i; for(i = 0; i < 10;++i) printf("%d %d %d\n",i,power(2,i),power(-3,i)); return 0; } /* power: raise base to the nth power;n >=0 */ int power(int base,int n) { int i , p; p = 1; for(i = 1;i <= n;++i) p = p * base; return p; }

我了解所有功能函数的代码块。 令我困惑的是循环。 我仍然在学C（显然，我在第一章），但我来自JavaScript。 所以当我看到这个循环时，我期望i需要被“绑定”到某个东西，以便它在我们的迭代中（类似于示例中的第一个for循环）。 但幂函数​​在p = p * base;后returns p p = p * base; 。 这与i没有任何关系。 对我来说，我认为，这个for循环的目的是什么？ 我注意到，如果我注释掉for循环并删除整数i那么打印出来的数字除了之前for循环中的数字之外不会增加。 对我而言，我期望int n需要增加。 不是i 。

在我看来，在for循环中， n仅用于与i进行比较。 如果i <= n为真，power函数中for循环的目的仅仅是为了执行p = p * base ？ 这不可能是真实的，因为如果那样的话，它最好只是一个if语句的服务器，并且不需要++i来递增。

我在这里错过了什么？

I am having trouble understanding the example 1.7 given in The C Programming Language. The main purpose of this example is to illustrate the use of functions in C. The book describes the following program as such, "Since C has no exponentiation operator like ** of Fortran, let us illustrate the mechanics of function definition by writing a function power(m,n) to raise an integer m to a positive power n. That is, the value of power(2,5) is 32. This function is not a practical exponentiation routine since it handles only positive powers of small integers, but it's good enough for illustration." This is the block of C code that follows:

#include <stdio.h> int power(int m, int n); /*function prototype */ int main() { /* test power function */ int i; for(i = 0; i < 10;++i) printf("%d %d %d\n",i,power(2,i),power(-3,i)); return 0; } /* power: raise base to the nth power;n >=0 */ int power(int base,int n) { int i , p; p = 1; for(i = 1;i <= n;++i) p = p * base; return p; }

I understand everything up to the power function's code block. What is confusing me is that for loop. I am still learning C(obviously, i'm in the first chapter) but I come from JavaScript. So when I see this for loop I expect the i to need to be 'bound' to something for it to be of us in iteration(similar to the first for loop in the example). But the power function returns p after p = p * base;. It's not returning anything to do with i. So to me, I think, what is the purpose of this for loop? I notice that if I comment out the for loop and remove the integer i then the numbers printed out do not increment except for the numbers within the previous for loop. To me, I expect the int n would need to increment. Not the i.

It appears to me that within the for loop that n is only being used as comparison to i. Is the purpose of the for loop in the power function only to execute p = p * base if i <= n is true? That can't be true because if that was then it would better be server with just an if statement and wouldn't need a ++i to increment.

What am I missing here?

最满意答案

power函数中的for循环反复地乘以（并更新） p 。 它做了n次 - i是柜台。 如果使用了if语句，那么您只能得到一个乘法。

The for-loop in the power function repeatedly multiplies (and updates) p by base. It does this n times -- i is the counter. If an if-statement were used, then you'd only get up to one multiplication.