FSX said:How difficult is it to convert "Algorithms + Data structures = Programs
by N. Wirth"'s examples to C?
osmium said:I have done that a few times and don't remember any particular difficulty.
FSX said:Great! Can you post or send them? It would be great since I know almost
nothing about pascal and I have that book lying on a shelf...
osmium said:Sorry. They were embedded in bigger works and I have no idea where they are
now. It was several years ago.
FSX said:So expect some questions at least... =) Do you think it's a good idea to post
questions about pascal conversion to C here? Thanks in advance...
Questions about conversion of code from another language to C, or vice
versa are equally appropriate here or in a group devoted to the other
language, such as comp.lang.pascal. However, for best results I'd
recommend cross-posting the question to both groups.
Richard Heathfield said:FSX said:
(snip)
But generally it isn't that hard, honest!
FSX said:How difficult is it to convert "Algorithms + Data structures = Programs
by N. Wirth"'s examples to C?
FSX said:
Hello,How difficult is it to convert "Algorithms + Data structures =
Programs by N. Wirth"'s examples to C?
Not too bad.
Let's take a frinstance. In my copy it's on p15 (copy-typed, so
please forgive any unwitting unPascalisms - and I may have changed
the spacing a bit):
program power(output);
{ decimal representation of negative powers of 2}
const n = 10;
type digit = 0..9;
var i, k, r: integer;
d: array[1..n] of digit;
begin for k := 1 to n do
begin write('.'); r := 0;
for i := 1 to k - 1 do
begin r := 10 * r + d; d := r div 2;
r := r - 2 * d; write(chr(d+ord('0')))
end;
d[k] := 5; writeln('5');
end
end .
Here's the C version, which is as close a translation as I can
reasonably manage without taking ages over it:
/* program: power
*
* decimal representation of negative powers of 2
*
* translated into C from [Wirth 1976] - the translation
* is as precise as I can make it (in a reasonably short
* time), so it will reflect Wirth's style rather than mine.
* I have, however, translated 1-based indexing into
* 0-based indexing.
*
*/
#include <stdio.h>
#define n 10 /* why not const? because no VLAs in C90! */
int main(void)
{
int i, k, r;
int d[n];
for(k = 0; k < n; k++)
{
putchar('.');
r = 0;
for(i = 0; i < k; i++)
{
r = 10 * r + d;
d = r / 2;
r = r - 2 * d;
putchar(d + '0');
}
d[k] = 5;
puts("5");
}
return 0;
}
And here's the output:
.5
.25
.125
.0625
.03125
.015625
.0078125
.00390625
.001953125
.0009765625
which is identical to Wirth's output.
I think the main gotchas in translating this book's code examples
into C are:
1) sets (for which C has no direct equivalent);
2) indexing (1-based makes for some strange contortions - the C
version will generally be simpler);
3) pointers - the p^ syntax is a little strange until you get used
to it.
But generally it isn't that hard, honest!
r = 10 * r + d;
Anand said:(...)/* program: power
*
* decimal representation of negative powers of 2
*
* translated into C from [Wirth 1976] - the translation
* is as precise as I can make it (in a reasonably short
* time), so it will reflect Wirth's style rather than mine.
* I have, however, translated 1-based indexing into
* 0-based indexing.
*
*/
#include <stdio.h>
#define n 10 /* why not const? because no VLAs in C90! */
int main(void)
{
int i, k, r;
int d[n];
for(k = 0; k < n; k++)
{
putchar('.');
r = 0;
for(i = 0; i < k; i++)
{
r = 10 * r + d;
d = r / 2;
r = r - 2 * d;
putchar(d + '0');
}
d[k] = 5;
puts("5");
}
return 0;
}
Don't know what Pascal's initialisation semantics are, but isn't this
line of code -r = 10 * r + d;
- using uninitialised elements of the array 'd'?- Anand
As far as I can see no, because when they enter that loop the 1st time
at least 1 value will be filled in. During the first run of the first
for loop the inner for loop is not executed.
FSX said:Hello,
How difficult is it to convert "Algorithms + Data structures = Programs
by N. Wirth"'s examples to C?
Cheers,
FSX
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