[Tip] Wean yourself off of parallel arrays

[wtd]

So you want to keep multiple pieces of information about a collection of things.

code:

var student_first_names : array 1 .. 10 of string var student_last_names : array 1 .. 10 of string var student_years : array 1 .. 10 of int var student_grades : array 1 .. 10 of int

This seems relatively obvious, but now you have four separate arrays to keep synchronized. Imagine passing all of that into a function or procedure, for instance.

Now, let's consider the alternative.

code:

type student : record     first_name : string     last_name : string     year : int     grade : int end record var students : array 1 .. 10 of student

Or even better, perhaps.

code:

type name_type : record     first : string     last : string end record type student_type : record     name : name_type     last_name : string     year : int     grade : int end record var students : array 1 .. 10 of student_type

code:

procedure print_student_with_name (lffn : string, lfln : string, fn : array 1 .. 10 of string, ln : array 1 .. 10 of string, y : array 1 .. 10 of int, g : array 1 .. 10 of int)     for i : 1 .. 10         if fn (i) = lffn and ln (i) = lfln then             put ln (i), ', ', fn (i), ' - year: ', y (i), '; grade: ', g (i)         end if     end for end print_student_with_name

vs.

code:

procedure print_student_with_name (lffn : string, lfln : string, students : var 1 .. 10 of student_type)     for i : 1 .. 10         if students (i).name.first = lffn and students (i).name.last = lfln then             put students (i).name.last, ', ', students (i).name.first, ' - year: ', students (i).year, '; grade: ', students (i).grade         end if     end for end print_student_with_name

Or maybe...

code:

procedure print_student_info (fn : string, ln : string, year : int, grade : int)     put ln, ', ', fn, ' - year: ', year, '; grade: ', grade end print_student_info procedure print_student_with_name (lffn : string, lfln : string, fn : array 1 .. 10 of string, ln : array 1 .. 10 of string, y : array 1 .. 10 of int, g : array 1 .. 10 of int)     for i : 1 .. 10         if fn (i) = lffn and ln (i) = lfln then             print_student_info (fn (i), ln (i), y (i), g (i))         end if     end for end print_student_with_name

vs.

code:

procedure print_student_info (student : student_type)     put  student.name.last, ', ', student.name.first, ' - year: ', student.year, '; grade: ', student.grade end print_student_info procedure print_student_with_name (lffn : string, lfln : string, students : array 1 .. 10 of student_type)     for i : 1 .. 10         if students (i).name.first = lffn and students (i).name.last = lfln then             print_student_info (students (i))         end if     end for end print_student_with_name

Edit by Clayton: Just a minor correction in the last example. Good job wtd!

[Mackie]

Great tip! +10 bits.

[wtd]

A prime example of the nastiness inflicted by using parallel arrays: http://compsci.ca/v3/viewtopic.php?t=17930