Create a two-dimensional array at runtime

Get two integers from the user, then create a two-dimensional array where the two dimensions have the sizes given by those numbers, and which can be accessed in the most natural way possible. Write some element of that array, and then oputput that element. Finally destroy the array if not done by the language itself.

Ada

with Ada.Text_Io; use Ada.Text_Io;
with Ada.Float_Text_Io; use Ada.Float_Text_Io;
with Ada.Integer_Text_Io; use Ada.Integer_Text_Io;

procedure Two_Dimensional_Arrays is
   type Matrix_Type is array(Positive range <>, Positive range <>) of Float;
   Dim_1 : Positive;
   Dim_2 : Positive;
begin
   Get(Item => Dim_1);
   Get(Item => Dim_2);
   -- Create an inner block with the correctly sized array
   declare
      Matrix : Matrix_Type(1..Dim_1, 1..Dim_2);
   begin
      Matrix(1, Dim_2) := 3.14159;
      Put(Item => Matrix(1, Dim_2), Fore => 1, Aft => 5, Exp => 0);
      New_Line;
   end;
   -- The variable Matrix is popped off the stack automatically
end Two_Dimensional_Arrays;

C

With language built-in facilities:

#include <iostream>
#include <istream>
#include <ostream>

int main()
{
  // read values
  int dim1, dim2;
  std::cin >> dim1 >> dim2;

  // create array
  double* array_data = new double[dim1*dim2];
  double** array = new double*[dim1];
  for (int i = 0; i < dim1;   i)
    array[i] = array_data   dim2*i;

  // write element
  array[0][0] = 3.5;

  // output element
  std::cout << array[0][0] << std::endl;

  // get rid of array
  delete[] array;
  delete[] array_data;
}

Using std::vector from the standard library:

#include <iostream>
#include <istream>
#include <ostream>
#include <vector>

int main()
{
  // read values
  int dim1, dim2;
  std::cin >> dim1 >> dim2;

  // create array
  std::vector<std::vector<double> > array(dim1, std::vector<double>(dim2));

  // write element
  array[0][0] = 3.5;

  // output element
  std::cout << array[0][0] << std::endl;

  // the array is automatically freed at the end of main()
}

Clean

import StdEnv

Start :: *World -> { {Real} }
Start world
    # (console, world) = stdio world
      (_, dim1, console) = freadi console
      (_, dim2, console) = freadi console
    = createArray dim1 (createArray dim2 1.0)

Common Lisp

(let ((d1 (read))
      (d2 (read)))
  (assert (and (typep d1 '(integer 1)) 
               (typep d2 '(integer 1))) 
          (d1 d2))
  (let ((array (make-array (list d1 d2) :initial-element nil))
        (p1 0)
        (p2 (floor d2 2)))
    (setf (aref array p1 p2) t)
    (print (aref array p1 p2))))

The assert will allow the user to reenter the dimensions if they are not positive integers.

Java

import java.io.*;

public class twoDimArray {
  public static void main(String[] args) {
     try {
        BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
        
        int nbr1 = Integer.parseInt(in.readLine());
        int nbr2 = Integer.parseInt(in.readLine());
        
        Double[][] array = new Double[nbr1][nbr2];
        array[0][0] = 42.0;
        System.out.println("The number at place [0 0] is "   array[0][0]);
        
     } catch(IOException e) { }
  }
}

Perl

Interpreter: Perl 5.x

Predefining an array (or multi-dimension array) size is unnecessary, Perl dynamically resizes the array to meet the requirements. Of course I'm assuming that the user is entering array size 0 based.

sub make_array($ $){
  # get array sizes from provided params, but force numeric value
  my $x = ($_[0] =~ /^\d $/) ? shift : 0;
  my $y = ($_[0] =~ /^\d $/) ? shift : 0;
  
  # define array, then add multi-dimensional elements
  my @array;
  $array[0][0] = 'X '; # first by first element
  $array[5][7] = 'X ' if (5 <= $y and 7 <= $x); # sixth by eighth element, if the max size is big enough
  $array[12][15] = 'X ' if (12 <= $y and 15 <= $x); # thirteeth by sixteenth element, if the max size is big enough
  
  # loop through the elements expected to exist base on input, and display the elements contents in a grid
  foreach my $dy (0 .. $y){
    foreach my $dx (0 .. $x){
      (defined $array[$dy][$dx]) ? (print $array[$dy][$dx]) : (print '. ');
    }
    print "\n";
  }
}

Python

Interpreter: Python 2.5

 width = int(raw_input("Width of array: "))
 height = int(raw_input("Height of Array: "))
 array = [[0] * width for i in range(height)]
 array[0][0] = 3.5

Note: Some people may instinctively try to write array as [[0] * with] * height, but the * operator creates n references to [[0] * width]

IDL

The following is only for demonstration. No real program should just assume that the user input is valid, integer, large enough etc.

read, x, prompt='Enter x size:'
read, y, prompt='Enter y size:'
d = fltarr(x,y) 

d[3,4] = 5.6
print,d[3,4]
;==> outputs  5.6

delvar, d