chap03 - QBASIC Chapter 3 QBASIC Chapter 3 Calculations,...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: QBASIC Chapter 3 QBASIC Chapter 3 Calculations, Strings, and An Introduction Calculations, to the Top-Down Approach to Created by Richard D. Taylor Illustrated by Saundra J. Taylor Introduction Introduction ­ Focus of the chapter ­Constants, variables, expressions, functions, Constants, rounding and truncation techniques rounding ­Type of data that can be assigned to variables ­Presents top-down, or modular approach to Presents solving problems solving Constants Constants ­ Numeric Constants - one of three forms: ­Integer - a positive or negative whole number Integer with no decimal point with ­Fixed Point - a positive or negative real number Fixed with a decimal point with ­Exponential Form - A number written as an Exponential integer or fixed point constant followed by the letter D or E and an integer (D or E stand for 10 times the power) times Constants Constants ­ Numeric Constants in Exponential Form ­expressed as a value between 1 and 10 expressed multiplied by a power of 10 multiplied ­1.5 X 106 written as 1.5E6 or 1.5 D6 ­ Numeric Constants in Scientific Notation ­represents the fact that the decimal point was represents moved X places to the right moved ­0.000000001234 written as 1.234E-9 / 1.234D-9 Constants Constants ­ Type and Range of Numeric Constants ­Short Integer -32,768 to + 32,767 ­Long Integer -2,147,483,648 to +2,147,483,648 ­Single Precision -3.4DE+38 to 3.40E+38 with Single up to 7 digits of significance up ­Double Precision -1.8+3D8 to +1.790+3D8 with Double up to 15 digits of significance up Constants Constants ­ String Constants ­has as its value the string of all characters has between surrounding quotation marks between ­Length - 0 - 32,767 characters ­Null String 0r Empty String - a string with a Null length of zero length ­INPUT “Customer’s Name”; first.name ­PRINT first.name$: “’s neck size is”; Neck.size Variables Variables ­ Simple Variables - used to store single values ­ Subscripted Variable - used to store groups of Subscripted values values ­ Numeric Variable - assigned only a numeric Numeric value value ­ String Variable - assigned a string of characters Variables Variables ­ Selection of Variable Names ­can be up to 40 characters in length ­must begin with a letter, followed by up to 39 must characters (letters, digits, or periods) characters ­if a variable name ends with a $, it is labeled a string if variable variable ­Reserved words cannot be used, as LET, PRINT, Reserved and END and Variables Variables ­ Selection of Variable Names ­not case-sensitive ­make variable names as meaningful as possible The LET Statement The LET Statement ­ Form: LET numeric variable = numeric LET expression expression LET string variable = string LET expression expression ­ Purpose:Causes the evaluation of the Purpose:Causes expression, followed by the assignment of the resulting value to the variable to the left of the equal sign of The LET Statement The LET Statement ­ Examples: ­ LET Perimeter = 2 * Side l + 2 * Side2 ­ LET Q = (B + A) / 2 - Q + R ­ Count = Count + 1 ­ NOTE: the keyword LET is optional Expressions Expressions ­ Numeric Expressions ­consists of one or more numeric constants, consists numeric variables, and numeric function references, all of which are separated from each other by parentheses and arithmetic operators other ­ Modulo Operator ­returns the integer remainder of integer returns division division Expressions Expressions ­ String Expression ­consists of one or more string constants, string consists variables and string function references separated by the concatenation operator (+) separated ­ Concatenation Operator (+) ­which joins two strings into one Expressions Expressions ­ Formation of Numeric Expressions ­the definition of a numeric expression dictates the the manner in which a numeric expression is to be validly formed validly ­A = 2B A=2*B ­ Evaluation of Numeric Expressions ­reading from left to right, then exponentiations, then reading multiplication /division, and addition/subtraction multiplication Expressions Expressions ­ Parentheses may be used to change the order Parentheses of operation and are normally used to avoid ambiguity and to group terms in a numeric expression expression () Expressions Expressions ­ Construction of Error-Free Numeric Expression ­Do not attempt to divide by zero ­Do not attempt to determine the square root of a Do negative value negative ­Do not attempt to raise a negative value to a Do nonintegral value nonintegral ­Do not attempt to compute a value that is greater Do than the largest permissible value or less than the smallest permissible nonzero value for the PC smallest Expressions Expressions ­ Numeric Functions ­INT Function - returns the largest integer not INT greater than the argument ­Argument - a number or numeric expressions Argument surrounded by parentheses that immediately follow the word follow ­ SQR Function ­returns the square root of the positive argument Expressions Expressions ­ Rounding and Truncation - Steps to ­Hat.Size = Hat.Size + .005 ­Hat.Size = Hat.Size * 100 ­Hat.Size = INT(Hat.Size) ­Rounded.Hat.Size = Hat.size / 100 Expressions Expressions ­ String Expression ­joining of two strings into one string ­PRINT City$ + “,” + ST$ Expressions Expressions ­ Use of LEFT$, LEN, MID$, and RIGHT$ Use String Functions String ­LEFT$(X$, N) - returns the left most N characters LEFT$(X$, of the string argument X$ of ­MET(X$) - returns the number of characters in the MET(X$) value associated with the string argument X$ value NOTE: Where X$ is a string expression, and N NOTE: and P are numeric expressions and Expressions Expressions ­ Use of LEFT$, LEN, MID$, and RIGHT$ Use String Functions String ­MDI$(X$,P,N) - returns N characters of the string MDI$(X$,P,N) argument X$ beginning at P argument ­RIGHT$(N$,N) - returns the rightmost N characters RIGHT$(N$,N) of the string argument X$ of NOTE: Where X$ is a string expression, and N NOTE: and P are numeric expressions and The Top­Down (Modular) Approach and the The Top­Down (Modular) Approach and the GOSUB and RETURN Statements ­ Top-down Approach - to take the original Top-down problem and break it into smaller and more manageable sub-problems, each of which is easier to solve than the original one easier The Top­Down (Modular) Approach and the The Top­Down (Modular) Approach and the GOSUB and RETURN Statements ­ Four Major Steps ­Problem analysis ­Top-down design - a strategy that breaks large, Top-down complex problems into smaller less complex problems and then decomposes each of these into even smaller problems even The Top­Down (Modular) Approach and the The Top­Down (Modular) Approach and the GOSUB and RETURN Statements ­ Four Major Steps ­Top-down programming - a strategy that codes Top-down high-level modules as soon as they are designed and generally before the low-level modules have been designed been ­Top-down testing and debugging - a strategy that Top-down tests and debugs the high-level modules of a system before the low-level modules have been coded, possibly before they have been designed coded, The Top­Down (Modular) Approach and the The Top­Down (Modular) Approach and the GOSUB and RETURN Statements ­ Top-Down Design ­High-level design - identifies what tasks need to High-level be performed be ­Detailed design - addresses how the tasks should Detailed be performed be The Top­Down (Modular) Approach and the The Top­Down (Modular) Approach and the GOSUB and RETURN Statements ­ High-Level Design ­Identify the overall problem ­Identify the sub-problems, each sub-problem may Identify be further subdivided - this process continues until a level is reached where each problem identified is easily comprehended easily The Top­Down (Modular) Approach and the The Top­Down (Modular) Approach and the GOSUB and RETURN Statements ­ Top-Down Chart, Hierarchy Chart or Visual Top-Down Table of Contents (VTOC) - graphical representation of the top-down design approach representation ­ Top-down Chart differs from a program Top-down flowchart in that it does not show decisionflowchart making logic but it shows organization and making functionality functionality The Top­Down (Modular) Approach and the The Top­Down (Modular) Approach and the GOSUB and RETURN Statements ­ Peer Review Group - composed of programmers Peer and analysts for further review and refinement, also called structured walk-through also The Top­Down (Modular) Approach and the The Top­Down (Modular) Approach and the GOSUB and RETURN Statements ­ Detailed Design ­how the tasks in the top-down chart should be how performed performed ­ Implementing a Top-Down Design Using Implementing subroutines (Modules) subroutines ­Subroutine or Module - each task in the top-down Subroutine chart chart ­Main module - highest level module in a program Main (level 0) (level The Top­Down (Modular) Approach and the The Top­Down (Modular) Approach and the GOSUB and RETURN Statements ­ Form: GOSUB label - where label is a line GOSUB label or line number that designates the beginning of a subroutine beginning ­ Purpose: Causes control to transfer to the Causes subroutine represented by label ­ Causes the location of the next executable Causes statement following the GOSUB to be retained statement The Top­Down (Modular) Approach and the The Top­Down (Modular) Approach and the GOSUB and RETURN Statements ­ Examples: ­GOSUB A100.Initialization ­GOSUB B200.Compute.Cost NOTE: In Qbasic, if label is a line label, rather NOTE: than a line number, then it must be followed immediately by a colon immediately The Top­Down (Modular) Approach and the The Top­Down (Modular) Approach and the GOSUB and RETURN Statements ­ Form: RETURN ­ Purpose: Causes control to transfer from the Causes subroutine back to the first executable statement immediately following the GOSUB statement that referenced it that ­ Examples: ­RETURN NOTE: The RETURN statement may be followed by a label The Top­Down (Modular) Approach and the The Top­Down (Modular) Approach and the GOSUB and RETURN Statements ­ Recommended Style and Tips When Using the Recommended Top-Down Approach Top-Down ­Start each subroutine with a comment box - a Start comment box consists of three or more remark lines with asterisks surrounding a brief comment with ­End each subroutine with a blank line ­Indent by three spaces the statements between the Indent subroutine name and the RETURN statement subroutine The Top­Down (Modular) Approach and the The Top­Down (Modular) Approach and the GOSUB and RETURN Statements ­ Recommended Style and Tips When Using Recommended the Top-Down Approach the ­So that lower-level subroutines can be located So easily for debugging purposes, they should be placed below the subroutine which calls them and in the order in which they are numbered in The Top­Down (Modular) Approach and the The Top­Down (Modular) Approach and the GOSUB and RETURN Statements ­ More About Subroutines ­Last statement should always be the RETURN Last statement, otherwise diagnostic message RETURN diagnostic without GOSUB without ­ Nested Subroutines ­one subroutine calling another subroutine but each one must have their own RETURN must ­Control stack - maintain locations of return when Control RETURN statements are executed RETURN The Top­Down (Modular) Approach and the The Top­Down (Modular) Approach and the GOSUB and RETURN Statements ­ Stubs ­a skeleton version of the final subroutine--it does skeleton not contain details or fulfill program tasks, it simply exists as the target of a GOSUB statement exists Summary Slide Summary Slide ­ Introduction ­ Constants ­ Variables ­ The LET Statement ­ Expressions ­ The Top-Down (Modular) Approach and The the GOSUB and RETURN Statements the ...
View Full Document

This note was uploaded on 06/06/2011 for the course MIS 105 taught by Professor Grigoletti during the Spring '11 term at Moraine Valley Community College.

Ask a homework question - tutors are online