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Article contents:== Input & output <table> <tr> <td></td> <td>CHICKEN</td> <td>C</td> <td>Python</td> <td>Perl</td> </tr> <tr> <td>Formatting and printing to stdout</td> <td><enscript highlight="scheme">(format #t "I want ~A ~A~%" count desc)</enscript></td> <td>printf("I want %d %s\n", count, desc);</td> <td><enscript highlight="python">print("I want {} {}\n".format(count, desc))</enscript></td> <td><enscript highlight="perl">say "I want $count $desc";</enscript></td> </tr> <tr> <td>Printing to stderr</td> <td><enscript highlight="scheme">(format (current-error-port) "Ooops~%")</enscript></td> <td>fprintf(stderr, "Ooops\n");</td> <td>...</td> <td><enscript highlight="perl">say STDERR 'Ooops';</enscript></td> </tr> <tr> <td>Reading a line from stdin</td> <td><enscript highlight="scheme">(read-line)</enscript></td> <td><enscript highlight="c">char buffer[1024]; fgets(buffer, sizeof(buffer), stdin);</enscript></td> <td>...</td> <td><enscript highlight="perl">&lt;STDIN&gt;</enscript></td> </tr> <tr> <td>Opening a file for input</td> <td><enscript highlight="scheme">(open-input-file path)</enscript></td> <td><enscript highlight="c">fopen(path, "r");</enscript></td> <td>...</td> <td><enscript highlight="perl">open my $fh, '&lt;', $path;</enscript></td> </tr> <tr> <td>Opening a file for output</td> <td><enscript highlight="scheme">(open-output-file path)</enscript></td> <td><enscript highlight="c">fopen(path, "w");</enscript></td> <td>...</td> <td><enscript highlight="perl">open my $fh, '&gt;', $path;</enscript></td> </tr> <tr> <td>Count lines in a file</td> <td><enscript highlight="scheme">(with-input-from-file path (lambda () (let loop ((count 0)) (if (eof-object? (read-line)) count (loop (+ count 1)))))))</enscript> </td> <td><enscript highlight="c">FILE *in = fopen(path, "r"); int c, count = 0; if (!in) handle_error(); while ((c = fgetc(in)) != EOF) if (c == '\n') lines ++; fclose(in); return count;</enscript></td> <td>...</td> <td><enscript highlight="perl"> open my $fh, '&lt;', $path; my $count = &gt;$fh&lt;; close $fh; </enscript</td> </tr> <tr> <td> Counting lines in a file if you don't want to keep an entire line in memory at any time: <td> <enscript highlight="scheme">(with-input-from-file path (lambda () (let loop ((count 0) (c (read-char))) (if (eof-object? c) count (loop (if (char=? c #\newline) (+ count 1) count) (read-char))))))</enscript> </td> <td>...</td> <td> <enscript highlight="python">f=open("file.txt", "rt") count=0 while True: c= f.read(1) if c == "": break if c == "\n": count = count + 1</enscript> </td> <td>...</td> </tr> <tr> <td>Write a file with some numbers In practice you'd probably collapse the calls to format and equivalent functions in a single call. </td> <td><enscript highlight="scheme">(with-output-to-file path (lambda () (format #t "~A~%" 1) (format #t "~A~%" 2) (format #t "~A~%" 3)))</enscript></td> <td><enscript highlight="c">FILE *out = fopen(path, "w"); if (!out) handle_error(); fprintf(out, "%d\n", 1); fprintf(out, "%d\n", 2); fprintf(out, "%d\n", 3); if (!fclose(out)) handle_error();</enscript></td> <td>...</td> <td><enscript highlight="perl"> open my $fh, '&gt;', $path; say $fh $_ foreach (1 .. 3); close $fh; </enscript></td></tr> </table> == Usage in a compiled program Some of the procedures listed here, e.g. {{(read-line)}} and {{(format ...)}}, are in the ''extras'' namespace, so if you are going to compile your program with {{csc}}, you'll need to add the following to your source file: (use extras) == Lists == Vectors <table> <tr> <td>Declaring a vector of numbers</td> <td>An anonymous vector is declared as: <enscript highlight="scheme">`#(1 2 ,x ,y 5)</enscript> To declare it as a global variable: <enscript highlight="scheme">(define *my-vector* `#(1 2 ,x ,y 5))</enscript> Or, to declare it locally for some body of code: <enscript highlight="scheme">(let ((vector `#(1 2 ,x ,y 5))) body-of-code ...)</enscript></td> <td> <enscript highlight="c">int vector[] = { 1, 2, x, y, 5 };</enscript> </td> </tr> <tr> <td>Obtaining the size of a vector</td> <td><enscript highlight="scheme">(vector-length my-vector)</enscript></td> <td>If the size of the vector is known at compile time: <enscript highlight="c">sizeof(my_vector)/sizeof(my_vector[0])</enscript> This often does not happen. If the vector is terminated with a special element (such as a NULL pointer or —as in the case of strings— a 0), you'll have to traverse it: <enscript highlight="c">int i; for (i = 0; my_vector[i] != SPECIAL_ELEMENT; i ++);</enscript></td> </tr> <tr> <td>Printing a vector</td> <td>If you don't care that much about the format used: <enscript highlight="scheme">(format "~A~%" vector)</enscript> If you need a newline after each element and can afford the vector to be converted to a list: <enscript highlight="scheme">(use format-modular) (format "~{~A~%~}" (vector->list vector))</enscript> Without converting the vector to list: <enscript highlight="scheme">(do ((i 0 (+ i 1))) ((= i (vector-length vector))) (format #t "~A~%" (vector-ref vector i)))</enscript> </td> <td> <enscript highlight="c">int i; for (i = 0; i < n; i ++) printf("%d\n", vector[i]);</enscript> </td> <td>...</td> </tr> </table> == Hash tables === Creating a hash table ==== CHICKEN <enscript highlight="scheme">(make-hash-table)</enscript> If you need to populate the hash table, you'll probably use {{alist->hash-table}}: <enscript highlight=scheme>(alist->hash-table '((1 . "uno") (2 . "dos")))</enscript> Note that the list can be created at runtime. ==== C++ STL <enscript highlight="cpp">map<int, string> my_hash; my_hash[1] = "uno"; my_hash[2] = "dos";</enscript> ==== Perl <enscript highlight="perl">my %hash = ( 1 => 'uno', 2 => 'dos' );</enscript> === Obtaining an element from a hash ==== CHICKEN <enscript highlight=scheme>(hash-table-ref/default my_hash 2 #f)</enscript> This will return {{#f}} (false) if the element is not defined. If you prefer to have an error thrown, you should use: <enscript highlight=scheme>(hash-table-ref my_hash 2)</enscript> ==== C++ STL <enscript highlight=cpp>my_hash[2]</enscript> ==== Python my_hash[2] ==== Perl <enscript highlight="perl">$my_hash{2}</enscript> === Printing the keys in the hash ==== CHICKEN If you can afford to have a list with the keys created, you should do this: <enscript highlight=scheme>(format #t "~{~A~%~}~%" (hash-table-keys my_hash))</enscript> Otherwise, do this: <enscript highlight=scheme>(hash-table-walk my-hash (lambda (key value) (format #f "~A~%" key)))</enscript> ==== C++ STL <enscript highlight="cpp">for(map<int, string>::iterator iter = my_hash.begin(); it != my_hash.end(); ++it ) cout << it->first << endl;</enscript> ==== Python print my_hash.keys() ==== Perl <enscript highlight=perl> say foreach keys %my_hash; </enscript> === Getting the number of items in a hash ==== CHICKEN <enscript highlight=scheme>(hash-table-size my-hash)</enscript> ==== Python <enscript highlight=python>len(my-hash)</enscript>Description of your changes:

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