Monday, January 28, 2008

Scheme For Enlightenment Part Five - Comparative Languages

The dreaded Scheme factorial example is written in C.

I'm coming most recently from the C world. What does it look like in C? C programmers usually think in loops, so something like this comes out.

int factorial(int x) {
register int product = 1;

do {
product *= x;
} while (--x);
return product;

The variable product is the factorial being built. In each loop, it is multiplied by the current x. The variable x is decremented by one. When the loop counts down to zero, the result is returned.

It's wickedly fast. And it works for positive arguments all the way up to 13. On 32 bit machines, factorial(14) is larger than an integer. Also, we didn't bother to check for zero (or less), so it loops for a long time before getting the wrong answer in these cases.

The fact that it is six or seven lines instead of three or four does not bother me. All of the lines are reasonably easy to read. Besides, C is free format. All the lines can be jammed together, even if it looks strange.

int factorial(int x) { int f = 1; do f *= x; while (--x); return f; }

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