1. Concepts of Programming Languages
Dr. Mohamed Yehia Dahab

2. Array Types
An array is an aggregate of homogeneous data elements in which an individual element is identified by its position in the aggregate, relative to the first element

3. Array Design Issues What types are legal for subscripts?
Are subscripting expressions in element references range checked?
When are subscript ranges bound?
When does allocation take place?
What is the maximum number of subscripts?
Can array objects be initialized?
Are any kind of slices allowed?

4. Array Indexing
Indexing (or subscripting) is a mapping from indices to elements
array_name (index_value_list)  an element
Index Syntax
FORTRAN, PL/I, Ada and matlab use parentheses
Ada explicitly uses parentheses to show uniformity between array references and function calls because both are mappings
Most other languages use brackets

5. Arrays Index (Subscript) Types
FORTRAN, C and Java: integer only
Ada and Pascal: any ordinal type (
program ideone;
type
Color = (Red, Orange, Black, White, Yellow, Green, Blue);
var
A1 : array [ ] of real;
A2 : array['A'..'Z'] of integer;
A3 : array[False .. True] of Color ;
A4 : array[Red .. Yellow] of integer;
 begin
A1[-5] := 3.1;
A2['C'] :=17;
A3 [True] := Red;
A4 [Yellow] := 55;
end.

6. Arrays Index (Subscript) Types (Cont’)
C, C++, Perl, and Fortran do not specify range checking (
#include <stdio.h>
int main(void) {
int Array[5];
Array[10] = 55;
printf("\n%d\n",Array[10]);
return 0; }

7. Arrays Index (Subscript) Types (Cont’)
Java, ML, matlab, and C# specify range checking
% Matlab Code
A=[ ];
display (A(1)) % display 55
display (A(0)) % index must be a positive integer or logical
display (A(4)) % display 9
display (A(5)) % Attempted to access A(5); index out of bounds because numel(A)=4
display (A(3>1)) % display 55
display (A(1>3)) % display []

8. Subscript Binding and Array Categories
Static: subscript ranges are statically bound and storage allocation is static (before run-time)
Advantage: efficiency (no dynamic allocation)
Fixed stack-dynamic: subscript ranges are statically bound, but the allocation is done at declaration time
Advantage: space efficiency

9. Subscript Binding and Array Categories (Cont’)
Stack-dynamic: subscript ranges are dynamically bound and the storage allocation is dynamic (done at run-time)
Advantage: flexibility (the size of an array need not be known until the array is to be used)
Fixed heap-dynamic: similar to fixed stack- dynamic: storage binding is dynamic but fixed after allocation (i.e., binding is done when requested and storage is allocated from heap, not stack)

10. Subscript Binding and Array Categories (continued)
Heap-dynamic: binding of subscript ranges and storage allocation is dynamic and can change any number of times
Advantage: flexibility (arrays can grow or shrink during program execution)

11. Subscript Binding and Array Categories (Cont’)
C and C++ arrays that include static modifier are static
C and C++ arrays without static modifier are fixed stack-dynamic
int Arr[20];
Ada arrays can be stack-dynamic
C and C++ provide fixed heap-dynamic arrays (using malloc/free or new/delete)
Perl and JavaScript support heap-dynamic arrays

12. C Language (Fixed Heap-dynamic)
Using malloc() function
Allocates requested size of bytes and returns a pointer first byte of allocated space
<pointer variable>=(<cast-type>*)malloc(<byte-size>);
Using free() function to dellocate the previously allocated space

13. Cuda C/C++ using cudaMalloc() (Fixed Heap-dynamic)
A void **  is just a pointer to a pointer to memory with an unspecified type
Host and device memory are separate entities
Device pointers point to GPU memory
Host pointers point to CPU memory
int size = 100 * sizeof (int);
int *d_a;
cudaMalloc((void **)&d_a, size); …
cudaFree(d_a);

14. C Language (Fixed Heap-dynamic) (Cont’)
#include <stdio.h>
#include <stdlib.h>
int main(){
int *ptr;
ptr=(int*)malloc(10*sizeof(int)); //memory allocated using malloc
if(ptr==NULL) {
printf("Error!");
exit(0); }
//using ptr
free(ptr);
return 0;

15. Java ArrayList (Heap-dynamic)
import java.util.*;
import java.io.*;
class TestArrayList {
public static void main (String[] args){
ArrayList A = new ArrayList();
A.add(30);
A.add(130);
A.add("3dfdf");
System.out.println(A.size());
System.out.println(A.get(1)); //zero based
System.out.println(A.get(2)); }
Heterogeneous Arrays

16. Java ArrayList (Heap-dynamic) (Cont’)
import java.util.*;
import java.io.*;
class TestGenericArrayList {
public static void main (String[] args){
ArrayList <Integer> intList = new ArrayList<Integer>();
ArrayList <String> stringList = new ArrayList<String>();
intList.add(30);
intList.add(10);
stringList.add("hggfhfg");
stringList.add("dgdfgdfgrtre");
System.out.println(intList.size());
System.out.println(stringList.get(1)); }

17. Array in Python A better analogy would be to the ArrayList class
Built-in functions and methods:
append()
remove()
len()
count(object)
+ for concatenation …
NumPy is an open-source add-on modules to Python that provide common mathematical and numerical routines in pre-compiled, fast functions

18. Array in Python (Cont’)
A.append(12)
A.insert(0,13)
print (A)
A[1] = 10
A = A * 3
R = range(4)
A = A + R
print (13 in A)
A.sort()
print (A[2:5])
A.append("erere")
[13, 12]
[13, 10, 13, 10, 13, 10]
[13, 10, 13, 10, 13, 10, 0, 1, 2, 3]
True
[0, 1, 2, 3, 10, 10, 10, 13, 13, 13]
[2, 3, 10]
Heterogeneous Arrays

19. Array Initialization
Some language allow initialization at the time of storage allocation
C, C++, Java, C# example
int list [] = {4, 5, 7, 83}
Character strings in C and C++
char name [] = “freddie”;
Arrays of strings in C and C++
char *names [] = {“Bob”, “Jake”, “Joe”];
Java initialization of String objects
String[] names = {“Bob”, “Jake”, “Joe”};

20. Arrays Operations
APL provides the most powerful array processing operations for vectors and matrixes as well as unary operators (for example, to reverse column elements)
Ada allows array assignment but also catenation
Fortran provides elemental operations because they are between pairs of array elements
For example, + operator between two arrays results in an array of the sums of the element pairs of the two arrays

21. Rectangular and Jagged Arrays
A rectangular array is a multi-dimensioned array in which all of the rows have the same number of elements and all columns have the same number of elements
A jagged matrix has rows with varying number of elements
Possible when multi-dimensioned arrays actually appear as arrays of arrays

22. Java is using Jagged arrays
Java Example
int array[][] = new int[3][];
array[0] = new int[3];
array[1] = new int[2];
array[2] = new int[5];
Java is using Jagged arrays
What about the following programming language:
Matlab
Pascal C
python

23. Slices
A slice is some substructure of an array; nothing more than a referencing mechanism
Slices are only useful in languages that have array operations

24. Slice Examples Fortran 95 Python Integer, Dimension (10) :: Vector
Integer, Dimension (3, 3) :: Mat
Integer, Dimension (3, 3, 4) :: Cube
Vector (3:6) is a four element array
Python
A[2:5] is a three element array

25. Slices Examples in Fortran 95