CSC115 Introduction to Computer Programming

1. CSC115 Introduction to Computer Programming Zhen Jiang Dept. of Computer Science West Chester University West Chester, PA 19383 zjiang@wcupa.edu

2. Table of Contents • Review of Basic I/O • Condition and Decision Making • Format/Syntax and Execution • Boolean Expression • Development • Multiple selection • Nested if • Code alignment and end of block • == and is

3. Review • Output • Number • String • Combination (by using + and str) • Input • Type • Conversion (float and int) • Processing • Feel it in the test

4. Condition and Decision Making • A deterministic output by a given input • Big-or-small? • Random.randint(1,6), store and not show • Guess 123 small or 456 big • Won or lost?

5. No Yes Condition Action 1 Action 2 Action 3

6. Yes No Boolean Expression Action 1 If controlled Action 2 else controlled Action 3

7. Syntax and Execution • If block if condition : action 1 (statements 1) else : action 2 (statements 2) # a blank line to separate action 3 (statement 3)

8. Boolean Expression • Simple condition • Format <Value> <relational operators> <Value> • Number value relational operators ==, !=, <, >, <=, >= !!! Number one error: “a=2” instead of “a==2” • String value relational operators left for later discussion • Complex condition • And, or, not • Truth table

9. Truth table • Precedence order • http://www.mathcs.emory.edu/~valerie/courses/fall10/155/resources/op_precedence.html

10. Relational operators have lower precedence than math operators. (7 - 1) * 5 + 3 > 7* 5 6 * 5 + 3 > 35 30 + 3 > 35 33 > 35 False Relational operators cannot be chained (unlike math operators) 2 <= x <= 10 error!

11. Development Process • Identify two exclusive options • Implement each handling in different action parts • Identify the situation (values) for option selection • Make a condition so that all the situation value for option part 1 will lead to this condition true. • Verify all the situation value for option part 2 will lead to this condition false, otherwise, revise the above condition!

13. Multiple selection • Nested if (chained condition) • Example: letter grade

14. Nested if for multiple section problem If then case 1 Else if then case 2 else … end if End if

16. Conditional and alternative execution if condition : action 1 (statements 1) # no else! action 3 (statement 3)

18. Are they different, how much? x = int(input("enter Int: "))y = 0if x > 3 : y = 1if x < 10 : y = 2else : y =3print(y) x = int(input("enter Int: "))y = 0if x > 3 : y = 1if x < 10 : y = 2else : y =3print(y)

19. Try 0, 4, 11 and see the results! 0 3 4 2 11 1 0 2 4 2 11 3

20. Indeed x = int(input("enter Int: "))y = 0if x > 3 : y = 1 if x < 10 : y = 2else : y =3print(y) x = int(input("enter Int: "))y = 0if x > 3 : y = 1if x < 10 : y = 2else : y =3print(y)

21. My point • One line in wrong place • Could cause the program 99.99% different • Location/alignment maters! • Blank line is useful • Structural procedure • Ask yourself where (the next program segment line) the computer execution goes • Before that, check if you can find the “if” for each “else”

22. Try enter “3” and “3”: a = int(input("first string: "))b = int(input ("second string: "))if a == b :print("same content")else:print("not the same content")if a is b :print ("same string")else:print ("not the same string")

23. Try this program and enter “3” and “3”. a = input("first string: ")b = input("second string: ")if a == b :print("same content")else:print("not the same content")if a is b :print ("same string")else:print ("not the same string")

24. Same code, try “a3” and “a3”. a = input("first string: ")b = input("second string: ")if a == b :print("same content")else:print("not the same content")if a is b :print ("same string")else:print ("not the same string")