CS 112: Intro to Comp Prog

Transcription

1 CS 112: Intro to Comp Prog Importing modules Branching Loops Program Planning Arithmetic Program Lab Assignment #2 Upcoming

2 Importing modules module: a file that contains external code that is related There are many different modules that have been created and are available to be used by your code. Importing loads the code and allows your program to access specific functions Example module: random Function: randrange(<bound>) #gets a number between 0 and (<bound> - 1)

3 if-structure if <condition>: <statements to perform when condition is true> <tabbing signifies which statements are contained> <within the if-block> <code not tabbed is always run> Example: num = int(raw_input("enter a number")) if (num % 2) == 0: print str(num)+" is even!" print "It is a good number"

4 if-else structure if <condition>: else: <statements to perform when condition is true> <...> <statements to perform when condition is false> <...> <code not tabbed is always run> Example: num = int(raw_input("enter a number")) if (num % 2) == 0: print str(num)+" is even!" else: print str(num)+" is odd!"

5 Conditions Conditions are expressions that evaluate to True or False Comparison Operators are used to create these expressions == equal to!= not equal to > greater than >= greater than or equal to < less than <= less than or equal to Examples: (10 / 2) == 5 True HELLO == hello False

6 Conditions Values in variables can also be directly evaluated to True or False Numeric: 0 == False, everything else is true String: == False, everything else is true Condition expressions can be combined/modified using Logical Operators not #negate the boolean value (false -> true) and #both sides of operator must be true or #at least one side of operator must be true There exists several parallels with if-statements and logical operators, and many times, solutions can be found through a variety of means.

7 Conditions if (num % 2)!= 0: print str(num)+" is odd! #Equivalent to: if not ((num % 2) == 0): print str(num)+" is odd!" if (num % 2) == 0 and (num % 3) == 0: print str(num)+" is divisible by 6!" #Equivalent to: if (num % 2) == 0: if (num % 3) == 0: print str(num)+" is divisible by 6!"

8 Conditions if userinput == "yes" or userinput == "YES": print "I am glad you feel that way" #Equivalent to: if userinput == "yes": print "I am glad you feel that way" if userinput == "YES": print "I am glad you feel that way"

9 if-elif-...-else structure if <condition1>: <statements to perform when condition1 is true> <...> elif <condition2>: <statements to perform when condition2 is true> <...> <...many elif statements may follow> else: <statements to perform when all above conditions> <are false> <...> <code not tabbed is always run>

10 if-elif-...-else structure Example: print "1. Print \"Hello\"" print "2. Print \"Good-bye\"" print "3. Print \"Zzzzzz\"" num = int(raw_input("enter your choice")) if num == 1: print "Hello" elif num == 2: print "Good-bye" elif num == 3: print "Zzzzzz" else: print "Not a valid choice"

11 while structure while <condition>: <statements to perform when condition is true> <tabbing signifies which statements are contained> <within the while-block. Once tabbed statements are> <executed program goes back to top to check> <condition again...repeat until false> <code not tabbed is always run, and is where code> <resumes when loop finishes, careful of infinite loops> Example: num = 0 while not num: num = int(raw_input("enter a non-zero number")) print "Hurray you chose: "+ str(num)

12 break continue Sometimes you may want to alter the way your loop runs from inside the loop rather than waiting for a single iteration of the loop to finish. We can do this with two commands: break - this will stop the loop and jump the program to run the code after the loop body (i.e. the tabbed code) continue - this will skip all lines of code inside the loop, jumping the program back to check the condition of the loop

13 A Top-Down Approach We can use a Top-Down approach to designing our program, these approach helps us keep the goal of the program in mind and not lose the forest for the trees Top-Down means looking from the big picture and breaking it down Example: An iron crowbar -> iron elements -> atoms -> protons, neutron, electrons ->... Thus we can identify a broad set of steps needed to accomplish our goal. These steps can be broken down into smaller stages and eventually into code

14 Program Planning Below is a series of steps you should go through either in your head or on paper to help you code your program. 1) Identify the Main Steps (Parts)...later make these into functions 2) Identify the Variables (Information) needed for each part or the entire program 3) Begin writing pseudo-code for each of steps 4) Revision (may take several revisions) 5) Convert pseudo-code into Python 6) Debug your code

15 Program Planning Write a program that will ask the user for two decimal numbers, then list a set of operations for them to choose (1 sum, 2 difference, 3 product, 4 quotient, 5 Quit). Display the solution to their choice. After the solution is printed redisplay the menu for them to choose another option until they choose 5, if they type any number other than 1-5 display an error message and continue to display the menu again. Terminal is as shown:

16 Identify the Main Steps Entering the two numbers Displaying the menu Entering a choice Branching for choice Repeating Menu

17 Identify the Variables Number 1 - num1 Number 2 - num2 User's Choice - choice Could have decided to have variables for each arithmetic operation, but will do the calculations in-line.

18 Pseudo-code Get user values for the two decimal numbers Create an infinite loop only to be stopped if 5 entered Print menu Get the user's choice of what operation to perform If choice is 1 print num1 + num2 If choice is 2 print num1 - num2 If choice is 3 print num1 * num2 If choice is 4 print num1 / num2 If choice is 5 stop the loop If choice is anything other than 1 5 restart loop ************************************************************** Take the time to convert the above pseudo-code into python code.

19 Arithmetic Prog Solution # Getting user values for the two numbers num1 = float(raw_input("enter Number 1: ")) num2 = float(raw_input("enter Number 2: ")) while 1: # Creating an infinite loop only to be stopped if 5 entered # Printing menu in single line with escape characters print "\n1-sum\n2-difference\n3-product\n4-quotient\n5-quit" # Getting the user's choice of what operation to perform choice = int(raw_input("choose your operation by typing the number(1-5): ")) if choice == 1: # Performing the proper actions based on the input 1-4 print "\nsum is " + str(num1 + num2) elif choice == 2: print "\ndifference is " + str(num1 - num2) elif choice == 3: print "\nproduct is " + str(num1 * num2) elif choice == 4: print "\nquotient is " + str(num1 / num2) elif choice == 5: else: break # Quitting # Restarting Loop print "\nbad Choice! Restarting..." continue

20 Arithmetic Prog Solution # Modify the condition of the loop to eliminate breaks and continues num1 = float(raw_input("enter Number 1: ")) num2 = float(raw_input("enter Number 2: ")) choice = 0 while choice!= 5: # Creating the choice variable so that it can be used by the condition # Creating an infinite loop only to be stopped if 5 entered print "\n1-sum\n2-difference\n3-product\n4-quotient\n5-quit" choice = int(raw_input("choose your operation by typing the number(1-5): ")) if choice == 1: # Performing the proper actions based on the input 1-4 print "\nsum is " + str(num1 + num2) elif choice == 2: print "\ndifference is " + str(num1 - num2) elif choice == 3: print "\nproduct is " + str(num1 * num2) elif choice == 4: print "\nquotient is " + str(num1 / num2) elif choice == 5: print "\nquitting..." else: # Restarting Loop print "\nbad Choice! Restarting..."