SFTW120-LectureNotes-15

# SFTW120-LectureNotes-15 - SFTW120 Programming Science...

This preview shows pages 1–4. Sign up to view the full content.

1 SFTW120 Programming Science Lecture Notes 15: Lisp: Selection Structures © Robert P. Biuk-Aghai SFTW120 - Programming Science 2 Lecture Notes 15 Lisp Selection Structures Lisp has 4 different selection structures: if – for choosing between two cases based on a test condition when – for conditionally evaluating a case based on a test form cond – for choosing between many cases based on a test condition case – for choosing between many cases based on a test condition (shorter than cond , but only works for symbols)

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
2 SFTW120 - Programming Science 3 Lecture Notes 15 if s When a selection between two cases is needed s Format of if statement: (if ( test-form ) ( then-form ) ( else-form )) s If test-form evaluates to non- NIL : evaluate then-form s If test-form evaluates to NIL : evaluate else- form SFTW120 - Programming Science 4 Lecture Notes 15 Example of if (if (leap year) (setq days-in-year 366) (setq days-in-year 365)) Sets the value of variable days-in-year to 366 if the function leap returns non- NIL for the given year , otherwise sets it to 365. The else-form is optional, e.g.: (if (leap year) (setq days-in-year 366)) Note: Assume that function leap has already been defined
3 SFTW120 - Programming Science 5 Lecture Notes 15 Grouping Multiple Expressions in if s Then-form and else-form can only have one expression each s To include more than one expression: group expressions using progn , e.g.: (if (leap year) (progn (setq days-in-year 366) (setq feb-days 29))

This preview has intentionally blurred sections. Sign up to view the full version.

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

## This note was uploaded on 05/04/2011 for the course SFST 120 taught by Professor Dr.robert during the Spring '11 term at University of Macau.

### Page1 / 10

SFTW120-LectureNotes-15 - SFTW120 Programming Science...

This preview shows document pages 1 - 4. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online