In Class: Week 3 Tuesday

Run update21 to Create a grab this week's files:

      $ update21
      $ cd cs21/inclass
      $ cd w03-boolean       
      $ pwd
      /home/your_user_name/cs21/inclass/w03-boolean
      $ ls
			contains_a.py  grade.py  noWhammy.py  tempConvert.py
	

Topics

• bool type and values True and False
• Conditional Statements
• Simple decisions with if statements
• Two-way decisions with if-else statements
• Multi-way decisions with if-elif-else statements
• Relational operators ==, !=, <, <e, >, >e
• Logical operators and, or, not
• Accumulation pattern with booleans using flag variables

We are going to do some of the following:

Conditional statements

1. One example use of conditionals is a temperature converting app. It would be wasteful to write two separate programs - one for converting from Fahrenheit to Celsius and then another app from the opposite. Let us use conditionals to combine the two together in tempConvert.py
2. After learning about multi-way branching, open up grade.py and try using a multi-way decision statement (a series of if-elif statements) to convert a student's numeric test score into a letter grade assuming a standard curve
3. Next, we will combine accumulation patterns with boolean variables in the program contains_a.py. We will write an algorithm that checks to see if a work contains the letter 'a'. We will use a boolean variable to assume there are no a's, and only change the value to True if an 'a' is found. containsA is a flag variable because it's value only changes to indicate a condition has been met at some point. Once its value has changed, it cannot go back. Here, once we find an 'a', containA should never go back to being false.
4. If you finish contains_a.py, try changing the algorithm so that it takes if there is an 'a' OR an 'A'. Once that is done, can we modify our algorithm to search if there is a second 'a'? This requires us to store the index of the first 'a' and begin the search anew but starting the for loop from the stored index.
5. Together, we will implement noWhammy.py. We'll ask the user to enter numbers and check to see if they enter the whammy value (e.g., 0). First, we'll use a boolean flag variable to see if they've entered the value whammy value. Notice that the game continues even after hitting a whammy since the for loop isn't finished. We'll add a break statement to immediately stop the loop.