CMP 131 Introduction to Computer Programming

1. CMP 131Introduction to Computer Programming Violetta Cavalli-Sforza Week 5, Lecture 2 (Tuesday)

2. TODAY • Input/Output and Formatting • Your questions on everything before the Quiz tomorrow

3. Input/Output (Read/Write) Procedures • Definitions: • Input Operation: • An instruction that reads data into memory. • Output Operation: • An instruction that displays information stored in memory. • Procedure: • A piece of code that is invoked from within the program and returns control to the program when finished • I/O Procedure: • Pascal procedure that performs I/O operation. • Procedure Call Statement: • An instruction that calls or activates a procedure.

4. Input/Output (Read/Write) Procedures • Data can be stored in memory in three different ways: • Associated as a constant • Assigned to a variable • Read into a variable • Reading is used if the data varies each time the program executes. • Input/output procedures are supplied as part of Pascal compiler. Their names are standard identifiers.

5. The Same Identifier has Different Meanings in Different Places • When a variable name occurs in a read/readln and a write/writeln statement, it has a different meaning: • write(MyVar) : MyVar is an expression The arguments to write are expressions (literals, constants, variables, combinations) whose value is retrieved for display • read(MyVar) : MyVar is interpreted as the address of a memory location to read into.You cannot have an expression as an argument to read • Similarly, when a variable name occurs in an assignment statement, it has a different value on the right hand side (RHS) of the := and on the left hand side of the := • On the RHS, it is (part of) an expression whose value is being retrieved • On the LHS, it is the address of a memory location where the RHS value will be stored.

6. Reading Data … • Procedures: read, readln • Read data from standard input device “input” (e.g. keyboard) • Syntax: read/readln(inloc1, inloc2, …, inlocN)inlocX is a location where to store the data • Examples: read(SqMeters); readln (Letter1, Letter2, Letter3); read (Age, FirstInitial) • Commas separate the variable names in input list

7. Reading Data … • Use write/writeln to display a prompt message when the user is required to enter data • Otherwise the program is waiting and you don’t know why or what to enter. • The order of data enter must correspond to the order of variables in the input list • Reading numeric data: • Insert one or more blanks between numeric data items • Reading character or string data: • Don't insert any blanks between consecutive data items unless the blank character is one of the data items being read

8. Read vs. Readline Procedure • Read: • Will read from input just as much as it needs for its arguments and leave the rest to be consumed later. • Extra characters on the data line after a read operation are not read until the next read or readln operation • Readln • Will read from input just as much as it needs for its arguments • It waits for a Return/Enter key character • Extra characters on the data line between what is needed and the end of line will be ignored after ReadLn is finished

9. PROGRAM ReadTest; VAR x,y: integer; BEGIN write('Type 2 integers separated by a space > '); read(x); writeln; writeln('Read x ',x); read(y); writeln; writeln('Read y ',y); writeln('Type ENTER to exit program.'); readln; END.

10. PROGRAM ReadLnTest; VAR x,y,z: integer; BEGIN writeln('Type 2 or more integers separated by a space.'); writeln('Terminate your input by pressing ENTER.'); readln(x,y); writeln('Read x ',x,' and y ',y); read(z); writeln('Read z ',z); END.

11. Writing/Displaying Data • Procedures: write, writeln • Write data to standard output device “output” (e.g. terminal) • Syntax: write/writeln(expr1, expr2, …, exprN)where exprX is an expression, whose value is to be written, with optional formatting information • Examples: writeln (Letter1, Letter2, Letter3); write (‘Age = ’, Age, ‘First Initial = ’,FirstInitial) write(SqMeters:10:2); • Commas separate the variable names in output list • Writes every argument in the output list in the order in which it is given.

12. write vs. writeln Procedure • writeln • used to display a line of program output, including a newline at the end; cursor advances to the next line after the output is displayed. • without any output list instructs the output device to advance by a blank line • write • Cursor doesn't advance to the next line after the output is displayed.

13. Self-Check • What is the output if the entered data are 5 7? writeln (‘Enter two integers>’); readln(M, N); M := M + 5; N := 3 + N; writeln (‘M = ‘, M); writeln (‘N = ‘, N); • What of the output of this code? write (‘My name is’); writeln (‘Doe, Jane’); writeln ; write(‘I live in ‘); write(‘Ann Arbor, MI’); writeln (‘and my zip code is ‘, 48109);

14. No Formatting with write/writeln • Integer values: take the space they need • Real values: Most Pascal compilers use scientific notation (floating-point notation) to display real values, but you can change that with formatting directives. • Character values display as themselves, without quotes • Boolean values display as FALSE and TRUE with no quotes • String literals, the characters inside the quotes are printed, but not the quotes themselves

15. PROGRAM TestOutputNoFormat; BEGIN writeln('An integer with no formatting : ', 45); writeln('A real with no formatting: ', 45.67); writeln('A character with no formatting: ', '#'); writeln('Boolean values, no formatting : ', false, ' and ', true); END.

16. Formatting Integer Output • Formatting Integer Values – b stands for blank space Value Format Printed Output 234 :4 b234 :5 bb234 :1 234 :Len bb234 (if Len=5) -234 :4 -234 :5 b-234 :1 -234

17. Formatting Integer Output • Add the symbol ‘:n’ to the integer output list item, where n specifies the number of digits to be displayed (field width). • The digits will be right-justified. • For negative numbers, the minus sign is included in the counts of digits displayed • The format specification ‘:1’ can always be used to display any integer values without leading blanks. • The field width specification may be a variable, or even an expression • The syntax for each integer item in an output list is: <integer expression>:<integer expression>

18. PROGRAM TestOutputIntFormat; VAR Dollars, Cents : integer; BEGIN Dollars := 5; Cents := 33; writeln('Your collection was worth '); writeln(Dollars : 1, ' dollars', ' and ', Cents :1, ' cents. '); writeln(Dollars : 2, ' dollars', ' and ', Cents :2, ' cents. '); writeln(Dollars : 3, ' dollars', ' and ', Cents :3, ' cents. '); writeln(Dollars : 4, ' dollars', ' and ', Cents :4, ' cents. '); writeln(Dollars : 5, ' dollars', ' and ', Cents :5, ' cents. '); Dollars := -2; Cents := 89; writeln('but is now worth '); writeln(Dollars : 1, ' dollars', ' and ', Cents :1, ' cents. '); writeln(Dollars : 2, ' dollars', ' and ', Cents :2, ' cents. '); writeln(Dollars : 3, ' dollars', ' and ', Cents :3, ' cents. '); writeln(Dollars : 4, ' dollars', ' and ', Cents :4, ' cents. '); writeln(Dollars : 5, ' dollars', ' and ', Cents :5, ' cents. '); END.

19. Formatting Real Output • Examples: b stands for blank space Value Format Printed Output 3.14159 :5:2 b3.14 :4:2 3.14 :3:2 3.14 :5:1 bb3.1 :8:5 b3.14159 :9 3.142E+00 -3.14159 :9 -3.14E+00 -124.3163 :4:2 -124.32

20. Formatting Real Output • Total field width & desired number of decimal places should be indicated. • Add “:n:d“ to the integer. • n = total field width • d = number of decimal digits. • Total field width should be large enough to accommodate all digits before and after the decimal point • Pascal will use the extra space it needs anyhow so your nicely formatted data may not look so well formatted after all. • Decimal point & sign for negative numbers are included in the count. • It is possible to use the form “:n“ for real numbers. In this case, the real value is printed in scientific notation using a total of n print positions.

21. Formatting Real Output • Eliminating Leading Blanks: • Choose a format that will display the smallest value expected without leading blanks.. • Examples: 29397 :1 is displayed as 29397 99397.567 :3:1 is displayed as 99397.6 • To display a real value without leading blanks, use format specification ‘:3:1’ for one decimal place or ‘:4:2’ for two decimal places. • If you use ‘:n’, the scientific notation will be displayed.

22. Formatting Character & String Output • Formatting Strings: • A string value is always printed right-justified in its field. • If the field width is too small to accommodate the string value, Pascal will take the space it needs. • Examples: bstands for blank space String Format Printed Value '*' :1 * :2 b* 'ACES' :1 ACES :2 ACES :3 ACES :4 ACES :5 bACES

23. PROGRAM TestOutputStringFormat; BEGIN writeln('ACES':1); writeln('ACES':2); writeln('ACES':3); writeln('ACES':4); writeln('ACES':5); writeln('ACES':6); END.

24. Self-Check • Show how the value -15.564 (stored in X) would be displayed using the following formats X :8:4 X:8:3 X:8:1 X:8:0 X:8 • Assuming X = 12.345 (type Real) and I = 100 (type Integer). What will the output of the following statements look like? writeln(‘X is ‘ :10, X :6:2, ‘I is ‘ :4, I :5); write(‘I is ‘ :10, I : 1); writeln(‘X is ‘ :10, X :2:1);