ice1341 programming languages spring 2005 lecture #14 lecture #14 in-young ko iko.at. icu.ac.kr...

ICE1341 ICE1341 Programming LanguagesProgramming Languages

Spring 2005Spring 2005

Lecture #14Lecture #14

In-Young Koiko .AT. icu.ac.kr

Information and Communications University (ICU)

Spring 2005 2 ICE 1341 – Programming Languages © In-Young Ko, Information and Communications University

Chapter 8 – Statement-Level Control Chapter 8 – Statement-Level Control StructuresStructures Selection StatementsSelection Statements Iterative StatementsIterative Statements

Last LectureLast Lecture


This LectureThis Lecture

Chapter 8 – Statement-Level Control Chapter 8 – Statement-Level Control StructuresStructures Unconditional BranchingUnconditional Branching Guarded CommandsGuarded Commands

FORTRAN ProgrammingFORTRAN Programming


Counter-Controlled LoopsCounter-Controlled Loops

Design IssuesDesign Issues::1. What are the 1. What are the typetype and and scopescope of the of the loop variableloop variable??

2. What is the 2. What is the valuevalue of the loop variable at of the loop variable at loop terminationloop termination??

3. Should it be legal for the loop variable or 3. Should it be legal for the loop variable or loop parameters loop parameters to be changed in the loop bodyto be changed in the loop body, and if so, does the , and if so, does the change affect loop control?change affect loop control?

4. Should the 4. Should the loop parameters be evaluatedloop parameters be evaluated only once, or only once, or once for every iteration?once for every iteration?

DO 20 N DO 20 N = 1, 100, 3= 1, 100, 320 SUM = SUM + N20 SUM = SUM + N

Loop VariableLoop Variable Initial ValueInitial Value

Terminal ValueTerminal Value

StepsizeStepsize

Lo

op

L

oo

p

Param

etersP

arameters


FORTRAN ‘DO’ LoopFORTRAN ‘DO’ Loop

Syntax: Syntax: DODO label var = start, finish [, stepsize] label var = start, finish [, stepsize]

StepsizeStepsize can be any value but zero can be any value but zero ParametersParameters can be expressions can be expressions

Design ChoicesDesign Choices::1. 1. Loop variableLoop variable must be must be integerinteger

2. 2. Loop variableLoop variable always has its always has its last valuelast value

3. The 3. The loop variable cannot be changedloop variable cannot be changed in the loop, but in the loop, but the the parameters canparameters can

4. 4. Loop parametersLoop parameters are evaluated only are evaluated only onceonce

* AW Lecture Notes


ALGOL 60 ‘For’ LoopALGOL 60 ‘For’ Loop Syntax: Syntax: forfor var := <list_of_stuff> var := <list_of_stuff> dodo statement statement

where <list_of_stuff> can have:where <list_of_stuff> can have: list of list of expressionexpressionss expressionexpression stepstep expressionexpression untiluntil expressionexpression expressionexpression whilewhile boolean_expressionboolean_expression

e.g., e.g., for index := 1 step 2 until 50,for index := 1 step 2 until 50, 60, 70, 80,60, 70, 80, index + 1 until 100 doindex + 1 until 100 do

(index = (index = 1, 3, 5, 7, ..., 49,1, 3, 5, 7, ..., 49,60, 70, 80, 81, 82, 83, ..., 100)60, 70, 80, 81, 82, 83, ..., 100)

ParametersParameters are evaluated with are evaluated with every iterationevery iteration, , making it very making it very complex and difficult to readcomplex and difficult to read

* AW Lecture Notes


‘‘For’ Loops in C-based LanguagesFor’ Loops in C-based Languages

Syntax: Syntax: forfor ([expr_1] ; [expr_2] ; [expr_3]) statement ([expr_1] ; [expr_2] ; [expr_3]) statement The expressions can be The expressions can be statement sequencesstatement sequences, with , with

the statements separated by commas or the statements separated by commas or nullnull

e.g., e.g., for (int i=0, j=10; for (int i=0, j=10; j==ij==i; ; i++, j--i++, j--)) printf(“%d, %d”, i, j);printf(“%d, %d”, i, j);

for (;;) …for (;;) … In In JavaJava, the , the control expressioncontrol expression must be must be BooleanBoolean

Design ChoicesDesign Choices::1, 2. There is 1, 2. There is no explicit loop variableno explicit loop variable

3. 3. Everything can be changedEverything can be changed in the loop in the loop

4. expr_1 is evaluated 4. expr_1 is evaluated onceonce,, others are evaluated with others are evaluated with each iterationeach iteration

Flexible!Flexible!


Other Counter-Controlled LoopsOther Counter-Controlled Loops

PascalPascalforfor variable := initial ( variable := initial (toto | | downtodownto) final ) final dodo

AdaAdaforfor var var inin [ [reversereverse] ] discrete_rangediscrete_range looploop ......end loopend loop The The loop variable is implicitly declared and loop variable is implicitly declared and

undeclaredundeclared as the loop begins and terminates as the loop begins and terminates

e.g., e.g., CountCount : Float := 1.35; : Float := 1.35; for for CountCount in 1..10 loop in 1..10 loop

Sum := Sum + Sum := Sum + CountCount;; end loopend loop

Count is an integer Count is an integer loop variableloop variable

Count is a float variableCount is a float variable


Logically Controlled LoopsLogically Controlled Loops

Posttest version executes the loop body Posttest version executes the loop body at least at least onceoncee.g., At the above examples, what happens if n is already e.g., At the above examples, what happens if n is already

greater than 100 before reaching to the loop?greater than 100 before reaching to the loop? PascalPascal – – whilewhile … … dodo, , repeatrepeat … … untiluntil AdaAda and and PerlPerl support support only pretest versionsonly pretest versions FORTRAN 77FORTRAN 77 and and 9090 support support neither versionneither version

whilewhile (n <= 100) { (n <= 100) {sum += n;sum += n;n += 3;n += 3;

}}

dodo { {sum += n;sum += n;n += 3;n += 3;

} } whilewhile (n <= 100) (n <= 100)

PretestPretest PosttestPosttest

Spring 2005 10

ICE 1341 – Programming Languages © In-Young Ko, Information and Communications University

User-Located Loop ControlUser-Located Loop Control

Design IssuesDesign Issues::

1. Should the 1. Should the conditionalconditional be part of be part of the exit?the exit?C-basedC-based – unconditional – unconditionalAdaAda – conditional ( – conditional (exit when …exit when …))

2. Can control be transferable out 2. Can control be transferable out of of more than one loopmore than one loop??JavaJava, , C#C#, , PerlPerl – – YesYes

whilewhile (n <= 100) { (n <= 100) {sum += n;sum += n;if (sum == m) if (sum == m) continuecontinue;;n += 3;n += 3;

}}

whilewhile (n <= 100) { (n <= 100) {sum += n;sum += n;if (sum == m) if (sum == m) breakbreak;;n += 3;n += 3;

}}

outout::forfor (int i=0; i<k; i++) { (int i=0; i<k; i++) {

whilewhile (n <= 100) { (n <= 100) { sum += n;sum += n; if (sum == m)if (sum == m) break break outout;; n += 3;n += 3;

}}}} JavaJava

Spring 2005 11


Iteration Based on Data Structures &Iteration Based on Data Structures &Unconditional BranchingUnconditional Branching

IBDS: Use order and number of IBDS: Use order and number of elements of elements of some data structuressome data structures to control iteration to control iteration

Unconditional Branching (Goto)Unconditional Branching (Goto) Problem: Problem: readabilityreadability – – Spaghetti LogicSpaghetti Logic Some languages do not have them: e.g., Java, Some languages do not have them: e.g., Java,

Modular-2Modular-2 Loop exit statementsLoop exit statements are restricted and somewhat are restricted and somewhat

camouflaged goto’scamouflaged goto’s

String[] String[] wdayswdays = { “Mon”, “Tue”, “Wed”, “Thu”, “Fri” }; = { “Mon”, “Tue”, “Wed”, “Thu”, “Fri” };……foreachforeach (String name (String name inin wdayswdays))

Console.WriteLine(“Work Day: {0}”, name);Console.WriteLine(“Work Day: {0}”, name); C#C#

Spring 2005 12


Guarded CommandsGuarded Commands (Dijstra, 1975) (Dijstra, 1975)

If more than one are true, If more than one are true, choose one choose one nondeterministicallynondeterministically

Runtime errorRuntime error when non of the when non of the conditions is trueconditions is true

ifif i = 0 -> sum := sum + i i = 0 -> sum := sum + i[][] i > j -> sum := sum + j i > j -> sum := sum + j[][] j > I -> sum := sum + I j > I -> sum := sum + Ififi

Allow Allow verificationverification during program development during program development Can be used to represent Can be used to represent concurrencyconcurrency

dodo q1 > q2 -> temp := q1; q1 := q2; q2 := temp; q1 > q2 -> temp := q1; q1 := q2; q2 := temp;[][] q2 > q3 -> temp := q2; q2 := q3; q3 := temp; q2 > q3 -> temp := q2; q2 := q3; q3 := temp;[][] q3 > q4 -> temp := q3; q3 := q4; q4 := temp; q3 > q4 -> temp := q3; q3 := q4; q4 := temp;odod If more than one are true, choose one nondeterministically; If more than one are true, choose one nondeterministically;

then then start loop againstart loop again; If none are true, ; If none are true, exit loopexit loop

Spring 2005 13


FORTRAN FORTRAN ((ForFormula mula TranTranslating System)slating System)

Designed to efficiently translate mathematical Designed to efficiently translate mathematical formulas into formulas into IBM 704IBM 704 machine code machine code

IBM 704IBM 704 (1954) (1954)““The first mass-produced The first mass-produced

computer with computer with core core memorymemory and and floating-floating-

point arithmeticpoint arithmetic”” Photo: Lawrence Livermore National Laboratory

Spring 2005 14


FORTRAN Coding FormatFORTRAN Coding Format

FORTRAN programs FORTRAN programs were written in a were written in a coding form with a coding form with a strict formatting rulestrict formatting rule

Continuation (6) Continuation (6)

FORTRAN Statement (7-72)FORTRAN Statement (7-72)

Identification Sequence (73-80)Identification Sequence (73-80)

Statement Number (1-5)Statement Number (1-5)

J.W. Perry Cole, ANSI FORTRAN IV,

wcb

Spring 2005 15


Punched CardsPunched Cards

Coded FORTRAN programs Coded FORTRAN programs were converted onto were converted onto

punched cards for loading punched cards for loading

Photos: http://www.tno.nl/instit/fel/museum/computer/en/punchcards.html

Spring 2005 16


Early FORTRAN VersionsEarly FORTRAN Versions

FORTRAN I (1957)FORTRAN I (1957) NamesNames could have up to could have up to six characterssix characters (IBM 704 has (IBM 704 has

a 6-bit BCD character set and 36-bit word)a 6-bit BCD character set and 36-bit word) Post-test counting loopPost-test counting loop ( (DODO), ), Formatted I/OFormatted I/O, , User-User-

defined subprogramsdefined subprograms, , Three-way selection Three-way selection statementstatement (arithmetic (arithmetic IFIF))

No data typing statements (No data typing statements (Implicit Type DeclarationImplicit Type Declaration – Variables whose names begin with I, J, K, L, M, – Variables whose names begin with I, J, K, L, M, and N are integer types, all others are floating point)and N are integer types, all others are floating point)

FORTRAN II (1958)FORTRAN II (1958) Independent compilationIndependent compilation of subroutines of subroutines

* AW Lecture Notes

Spring 2005 17


Later FORTRAN VersionsLater FORTRAN Versions

FORTRAN IV (1960-62) – ANSI standard in 1966FORTRAN IV (1960-62) – ANSI standard in 1966 Explicit type declarationsExplicit type declarations Logical selection statementLogical selection statement Subprogram names could be parametersSubprogram names could be parameters

FORTRAN 77 (1978)FORTRAN 77 (1978) Character stringCharacter string handling handling Logical loop control statementLogical loop control statement IF-THEN-ELSEIF-THEN-ELSE statement statement

FORTRAN 90 (1990)FORTRAN 90 (1990) Free coding formatFree coding format Modules, Dynamic arrays, Pointers, Recursion, Modules, Dynamic arrays, Pointers, Recursion, CASECASE

statementstatement* AW Lecture Notes

Spring 2005 18


A Sample FORTRAN ProgramA Sample FORTRAN Program

C *** This is a sample FORTRAN IV programC *** This is a sample FORTRAN IV program

PROGRAM SAMPLEPROGRAM SAMPLE

READ (5, 990) A, BREAD (5, 990) A, B

990990 FORMAT (F5.2, F5.2)FORMAT (F5.2, F5.2)

SUM = A + BSUM = A + B

WRITE (6, 81) A, B, SUMWRITE (6, 81) A, B, SUM

8181 FORMAT (1X, F5.2, 3X, F5.2, 3X, F6.2)FORMAT (1X, F5.2, 3X, F5.2, 3X, F6.2)

STOPSTOP

ENDEND

J.W. Perry Cole, ANSI FORTRAN IV, wcb

Spring 2005 19


FORTRAN Data Types (1)FORTRAN Data Types (1)

IntegerInteger Implicit TypingImplicit Typing: Variables whose names begin with I~N: Variables whose names begin with I~N Explicit DeclarationExplicit Declaration

e.g., e.g., INTEGER A, TOTALINTEGER A, TOTAL Real Real – Single precision floating point number– Single precision floating point number

Implicit TypingImplicit Typing: Variables whose names begin with : Variables whose names begin with other than A~H or O-Zother than A~H or O-Z

Explicit DeclarationExplicit Declaration

e.g., e.g., REAL J, RREAL J, R Double precisionDouble precision floating point number floating point number

e.g., e.g., DOUBLE PRECISION A, XDOUBLE PRECISION A, X

Spring 2005 20


FORTRAN Data Types (2)FORTRAN Data Types (2)

Complex Complex e.g., e.g., COMPLEX A, B, CCOMPLEX A, B, C

A = (3.5, -7.24)A = (3.5, -7.24) B = (-8.21, 5.67)B = (-8.21, 5.67) C = A + BC = A + B

CharacterCharactere.g., e.g., CHARACTER C, NAME*20, ADDR*30CHARACTER C, NAME*20, ADDR*30 CHARACTER*20 STR1, STR2CHARACTER*20 STR1, STR2

Character constants: e.g., Character constants: e.g., ‘C’‘C’,, ‘Go ICU’ ‘Go ICU’ Hollerith StringsHollerith Strings:: e.g., 1HC, 5HGoICU e.g., 1HC, 5HGoICU

LogicalLogical (Boolean) (Boolean)e.g., e.g., LOGICAL X, Y, FLAGLOGICAL X, Y, FLAG

Logical constants: Logical constants: .TRUE..TRUE. or or .FALSE..FALSE.

Spring 2005 21


Variable Initializations and ArraysVariable Initializations and Arrays

Variable InitializationsVariable Initializations

e.g., e.g., DATA A/1.0/, L/2/, B,C/4.0, 5.0/DATA A/1.0/, L/2/, B,C/4.0, 5.0/

DATA ARYX(3)/1.333/, DATA ARYX(3)/1.333/, T(1),T(2),T(3)/3*0.0/T(1),T(2),T(3)/3*0.0/

DATA C(1)/1HS/, C(2)/1HD/, TAG/3HYesDATA C(1)/1HS/, C(2)/1HD/, TAG/3HYes ArraysArrays

e.g., e.g., DIMENSION A(5), B(10,7), N(3,5,20)DIMENSION A(5), B(10,7), N(3,5,20)

INTEGER X(7,5)INTEGER X(7,5)

REAL MATRIX(-6:4, 7, -5:10), KREAL MATRIX(-6:4, 7, -5:10), K

DIMENSION K(20)DIMENSION K(20)J.W. Perry Cole, ANSI FORTRAN IV, wcb

Spring 2005 22


FORTRAN OperatorsFORTRAN Operators

Arithmetic Operators: Arithmetic Operators: ++, , --, , **, , //, , **** (exponentiation) (exponentiation) Mixed mode expressions – evaluated in integer mode Mixed mode expressions – evaluated in integer mode if all if all

operands are integeroperands are integer, evaluated in real mode otherwise, evaluated in real mode otherwisee.g., e.g., 86.3 * K + R / 16.5 ** J86.3 * K + R / 16.5 ** J All are evaluated in All are evaluated in

realreal

Relational Operators: Relational Operators: .LT..LT.,,.LE.LE.,.,.GT..GT.,,.GE..GE.,,.EQ..EQ.,,.NE..NE.e.g., e.g., IF (RESULT .LT. 0.0) STOPIF (RESULT .LT. 0.0) STOP

Logical Operators: Logical Operators: .AND..AND., , .OR..OR., , .NOT..NOT.e.g., e.g., IF (N .EQ. 1 .OR. .NOT. R .LT. 0.0) GOTO 75IF (N .EQ. 1 .OR. .NOT. R .LT. 0.0) GOTO 75

Multiple Assignment StatementsMultiple Assignment Statementse.g., e.g., A = I = V = W = .2 * R + XA = I = V = W = .2 * R + X A truncated value will be assigned to A and IA truncated value will be assigned to A and I

Spring 2005 23


Program Flow ControlProgram Flow Control

GotoGoto GOTO (10, 20, 30) KCOUNTGOTO (10, 20, 30) KCOUNT

Logical IFLogical IF IF (K .LT. 1) K = K + 1IF (K .LT. 1) K = K + 1

Arithmetic IFArithmetic IF IF (A / T – S) 10, 20, 30IF (A / T – S) 10, 20, 30

Block IFBlock IF IF (M .GT. 15) THEN M = M / 3IF (M .GT. 15) THEN M = M / 3ELSE M = M * 3ELSE M = M * 3ENDIFENDIF

Do loopsDo loops DO 10 I = 1, N, 2DO 10 I = 1, N, 2 SUM = SUM + ISUM = SUM + I

10 CONTINUE10 CONTINUE

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