Programming in QBasic

Transcription

1 Programming in QBasic Second lecture Constants In QBASIC: Constants In QBASIC division into three types: 1. Numeric Constants: there are two types of numeric constants: Real: the numbers used may be written in decimal form such as(6.9, ,0.095, ) Integer: Whole numbers may be written without the decimal point such as (89,-132,7698) Exponential Form: this form requires a number fallowed by the letter E, such as (2.8E05,0.57E-03,0.07E-9, and 29.8E7). 2. String Constants: a string consists of a sequence of characters enclosed in double quote marks. strings usually consist of names or address or cities such as "Computer", "Baghdad". Variables In QBASIC In QBASIC, variables are also of two types: 1. Numeric variable :Numeric variable can assume numeric value and is represented by an alphabet or an alphabet followed by another alphabet or digit. For example A, C, A2, ABC, A6etc, represent numeric variables. 2. String variable : A string variable is represented by an alphabet followed by dollar ($) sign. It should be kept in mind that while constructing the string variable, dollar ($) should be the last character. For example B1$, NAME$, BOOK1$, etc are valid string variables. Arithmetic Expression: Expressions are used in QBASIC in order to perform calculations. QBASIC can handle arithmetic expression involving the five arithmetic operators + (addition), - (subtraction), * (multiplication, / (division) and ^ (exponentiation). it is necessary to know that the QBASIC compiler using the following order of precedence in performing arithmetic operations:

2 In addition to this hierarchy of operations, the following rules must be kept in mind in arithmetic expression: Two operations must not appear together. For example, C+-D, A/-C, etc are not permitted. String constants and string variables should not be used in arithmetic expressions. For example P+P$ is wrong. When brackets are used, they must be used in pairs, i.e. every left bracket must be matched with a right bracket. Denominator of an expression should not be zero. Example (1): Write following expressions in appropriate formula in QBASIC language: Y=a.b-r.s+r 2 Expression Z = [(X + Y) + (X Y) ] A=s.r-y.z+x/5 A=PQ/CB R = ( )( ) Solve Y=a*b-r*s+r^2 Z=((X+Y))^2+(x/Y)^3)^(3/2) A=s*r-y*z+x/5 A=P*Q/(C*B) R=(s+b)*(a+d)/b Example (2): Suppose( a=5. b=4,c=2,i=2,j=1) Execute the following expressions in order of precedence: Expression Solve a+b+c/ /12= j/(i+c) 1/(2+2)=1/4=0.25 (j*(a^2-10))/2 (1*(5^2-10))/2=7.5

3 Library Functions Each basic interpreter has within it the capability of calculating certain special functions, sometimes called library functions. these functions are indicated by three letters naming the function, followed by argument enclosed in parentheses. the argument may be either a number, a variable, or a an expression. in the following table library functions as might be found in most basic interpreters. Function Description of function Exp(x) Log(x) ABS(x) SGN(x) The value of ex The natural logarithm of x,ln(x) Absolute value of x, x. =(-1 or 0 or 1) for (x<0 or x=0 or x>0). SQR(x) Square root of x. INT(x) The largest integer not exceeding x. RND(x) Create random number value between 0 and 1. Sin(x) Cos(x) Tan(x) Atn(x) Mod Div Sin of x, x in radians Cosine of x, x in radians Tangent of x, x in radians Arctangent of x, x in radians Modulus-Rest of division. Ex:10mod3=1 Integer division. Ex:10div3=3 Example: convert following mathematical expression in appropriate formula QBASIC :

4 Mathematical Expression Solve in QBASIC Y = 1 e 1 + e Y = 1 exp(x) /(1 + exp(x)) C = A B + C=A/SQR(B)+EXP(A+B)/ABS(A+B) A + B Y = cos(x) 2 sin (X) Y=cos(x*3.14/180)/2-sin(x*3.14/180)^2 e H.W: Write the following expressions in QBASIC language: Z= (A+B) 3 (a+ )n-3 e x+y sin(a+ ) T=t(l-d).y-t.(l-d)y P=(x+y)(x-y)/x 2 T= ( ).S Y=sin(x).cos(x)/cos 2 (x) W=3.e x. 1 + e Flow Charts A flowchart is a schematic representation of algorithm or the program flow using some set of standard symbols. The various basic symbols used are shown in the following Figure: Start of Program Program flow direction Output and Input operation

5 Arithmetic operation connecter Decision box Reparative symbol Program Statements in QBASIC: A statement (for the QBASIC) is a set of instructions written by using keywords or commands of QBASIC. Every programming language uses keywords as a statement with certain syntax. The keywords have specific meaning in the QBASIC programming. The statements are the first stored in the memory and executed only when the RUN command is given. 1- Rem Statement: Rem is a special keyword known as remark. Sometimes when a programmer write long program, he or she will like to leave notes inside their program so that they can remember why they did certain things. So to leave a note that explains certain things, use remark. QBASIC knows that when it sees Rem it does not have to do what you wrote after it on that line. The symbol ( ) also used as alternative to (Rem).

6 Example: Rem Program to compute area Program to compute area 2- Cls Statement: The simple CLS statement clears everything off of the screen and puts the cursor at the top left corner of the screen. Example: CLS 3- Let Statement: LET variable = expression The LET statement assigns a variable a value. variable is the name of any type of variable. expression is an arithmetic expression or a string expression. Examples: Let C=A+B*C Let J=J+1 Let C=SQR(A*A+B^2) Let A$="computer" 4- Print Statement: Print expression(, or;) expression Where expression is any number, any string of words, any variable, or any combination of numbers and variables in an algebraic expression. Commas or semicolons must be used to separate expressions. Comma provides a TAB space, but semicolon provides only one space. Example: PRINT "Computer is an electronic machine" PRINT "IT's amazing." PRINT 1000 PRINT " The number is: "; Statement: END statement is used to show the end of a program. Any statement written after END will not be executed. Example: write a program to compute the following function: A=X 2 +Y 2, Q=i 2 -yx-x/i, if (x=6,y=8,i=9)

7 Solution: Let x=6 Let y=8 Let i=9 Let A=x^2+y^2 Let Q=i^2-b*x-x/i Print A,Q Example: write a program to find the area and circumference of square. if length of the side (s=5). Start Solution: REM Program for compute square area and circumference S=5 S=5 A=s^2 C=4*s Print "the area=";a Print "the circumference=";c A=s^2 C=4*s Print A,C