Variable scope ppt in vb6

Defining Variables and it's type, its scope and common error that a user make while declaring a variable.

1. MY PRESENTATION TOPIC SCOPE OF VARIABLE MADE BY – Aman Hooda

2. VARIABLES VARIABLES ARE USED VISUAL BASICS TO STORE VALUES DURING A PROGRAM EXECUTION . WHEN NAMING YOUR VARIABLES FEW RULES MUST BE FOLLOWED . MUST BEGIN WITH A LETTER CAN HAVE UP TO 255 CHARACTERS. PLEASE, JUST BECAUSE IT IS ALLOWED, DON'T USE 255 CHARACTERS. MUST BE UNIQUE INSIDE OF THE PROCEDURE OR THE MODULE IT IS USED IN IT CAN CONTAIN LETTER, NUMBERS, UNDERSCORE(_). IT MUST NOT CONTAIN SPACES. TO DECLARE A VARIABLE, USE THE DIM STATEMENT FOLLOWED BY THE VARIABLE’S NAME AND TYPE , EXAMPLE – DIM A AS INTEGER. DIM ‘NAME’ AS STRING.

3. TYPES OF VARIABLES Types of Variables : Visual Basic recognizes the following six types of variables : Numeric : The different numeric data types provided are : (a) Integers (b) Single, or floating point numbers with limited precision (c) Double, or floating point numbers with extreme precision String : This data type stores only text and string variables are declared with the String type. Boolean : This data type stores True/False values. Date : Date and time values are double-precision numbers: the integer part represents the date and the fractional part represents the time. Object : An object variable refers to one of Visual Basic’s many objects, and you can use an object variable to access the actual object. Variant : This is the most flexible data type because it can accommodate all other types.

4. Variable Suffixes Variable Type Suffix Integer % Long & Single ! Double # Currency @ String $ Byte None Boolean None Variable Type Suffix Date None Object None Variant None

5. VARIABLE DECLERATION IS OF 2 TYPES IMPLICIT DECLERATION : To implicitly type a variable, use the corresponding suffix shown above in the data type table. For example, TextValue $ = "This is a string“ ‘creates a string variable. Amount% = 300 ‘creates an integer variable. IMPLICIT EXPLICIT

6. VARIABLE SCOPE THE SCOPE OF AN ELEMENT DEPENDS ON WHERE USER DECLARE IT : PROCEDURE SCOPE: AN ELEMENT DECLARED WITHIN A PROCEDURE IS NOT AVAILABLE OUTSIDE THAT PROCEDURE. ONLY THE PROCEDURE THAT CONTAINS THE DECLARATION CAN USE IT. VARIABLES AT THIS LEVEL ARE ALSO KNOWN AS  LOCAL VARIABLES . DECLARING VARIABLE WITH THE  DIM STATEMENT , WITH OR WITHOUT THE  STATIC KEYWORD. EXAMPLE: DIM CUBE AS INTEGER DIM MYDOUBLE AS DOUBLE PROCEDURE LEVEL VARIABLES DECLARED IN THIS MANNER, DO NOT RETAIN THERE VALUES ONCES A PROCEDURE TERMINATES. TO MAKE THE PROCEDURE LEVEL VARIABLE RETAIN THERE VALUES UPON EXISTING THE PROCEDURE, REPLACE THE WORD DIM WITH STATIC . EXAMPLE: STATIC CUBE AS INTEGER STATIC MYDOUBLE AS DOUBLE

7. EXAMPLE PROCEDURE SCOPE WITH AND WITHOUT STATIC

8. CONTINUED. MODULE SCOPE : FORM LEVEL VARIABLE DECLARES VARIABLES AT THE TOP OF THE FORM. DECLARE ELEMENTS AT THIS LEVEL BY PLACING THE DECLARATION STATEMENT OUTSIDE OF ANY PROCEDURE OR BLOCK BUT WITHIN THE MODULE, CLASS, OR STRUCTURE. IN THIS VARIABLES RETAIN THERE VALUES AND ARE AVAILIABLE TO ALL THE VARIABLE WITHIN THAT FORM. FORM LEVEL VARIABLES HAVE A LIFE AS LONG AS THE FORM / MODULE EXISTS. VARIABLE ARE DECLARED USING THE PUBLIC OR THE PRIVATE OR THE DIM KEYWORD. EXAMPLE: DIM LOGINPASSWORD AS STRING PRIVATE CUSTOMERNAME AS STRING

9. EXAMPLE: MODULE / FORM SCOPE

10. CONTINUED. GLOBAL SCOPE WHEN A VARIABLE IS DECLARED AS  GLOBAL  IT IS VISIBLE TO ALL PROCEDURES AND MODULES THAT COMPRISE THE APPLICATION. GLOBAL VARIABLES CANNOT BE USED AT FORM LOAD.

11. KEY POINTS TO REMEMBER DIFFERS FROM VISUAL BASIC 6.0 AND EARLIER VERSIONS, IN WHICH VARIABLES WHOSE TYPES WERE NOT EXPLICITLY DECLARED WERE CREATED AS VARIANTS. ONE CANNOT USE POTECTED TYPE VARIABLES IN FORM LOAD, AS INHERITANCE AND POLYMORPHISM IS NOT SUPPORTED BY VB 6. OPTION EXPLICIT IS SET OFF (BY DEFAULT, IT IS SET ON). VISUAL BASIC 6 IS EVENT BASED PROGRAMMING LANGUAGE RATHER THAN EVENT DRIVEN PROGRAMMING. CONTINUED.

12. ERROR: CONTINUED.

13. THANK YOU STAY HAPPY AND STAY SAFE EVERYONE