Loops, Subprograms - Programming Languages - Lecture Slides, Slides of Programming Languages

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Loops

• Simple Loop – unconditional infinite loop
• While loop
• For Loop

Simple Loop

loop -- Loop body goes here end loop ;

loop -- Loop body goes here if condition then exit ; end if ; end loop ;

loop -- Loop body goes here exit when condition ; end loop ;

Exit statement

• exit ;

• exit when condition;

• Can only be used in a loop

• You can use labels:

Outer : loop Inner : loop … exit Inner when Done; end loop Inner; end loop Outer;

Block Statement

• Block statement can be used anywhere

declare -- declare section optional declarations begin statements exception -- exception section optional handlers end ;

Declaring and Handling Exceptions

• Declaring an exception Error, Disaster : exception ;
• Raising an exception raise Disaster; -- strips stack frames till a handler is found
• Handling an exception exception when Disaster => statements

More on Exception Handling

• Anywhere we have begin-end, we can do:

begin statements exception when exception1 => statements ; when exception2 => statements ; end ;

Subprograms

Procedure My_procedure(x, y : IN OUT integer) is … function aux_func(a : Integer) return integer is Temp : float; begin … return integer(temp) * a; -- retrun temp * a is not allowed end aux_func; … begin … aux_func(x); … end My_procedure;

Type Name No return type

Parameter List – IN, OUT, IN OUT

Default mode is ‘IN’

You have to convert/cast^ Return type ‘Temp’ to an integer

Packages

• Packages are the primary structure used

for encapsulation in Ada

• Packages are used to group data and

subprograms

• Packages can be hierarchical, allowing a

structured and extensible relationship for

data and code

• All the standard Ada libraries are defined

within packages

package STACK is procedure PUSH (x : INTEGER); function POP return INTEGER; end STACK;

Package Specification

package body STACK isMAX: constant := 100; S : array (1..MAX) of INTEGER;TOP : INTEGER range 0..MAX; procedure PUSH (x : INTEGER) isbegin TOP := TOP + 1;S(TOP) := x; end PUSH; function POP return integer isTOP := TOP - 1; end POP;return S(TOP + 1); begin TOP := 0; end STACK;

Package Body

exception is raised and need^ If value of TOP>100, an to be handled