Lecture 3 - Exercises

3A - Operators and Operator Precedence

1. Evaluate each of the following expressions. Be sure to properly indicate the type of the value, for example by including a decimal point if the result is a float or enclosing it in double quotes if it’s a str.
   1. 9 / 3
   2. 9 // 3
   3. 10 // 3
   4. 10 % 3
   5. 3 % 10
   6. 2 ** 3
   7. "abc" + "def"
   8. "baa " * 2
2. Evaluate each of the following expressions. As before, be sure to be precise about the type of the resulting value.
   1. (9 % ( 6 // 2))
   2. 9 % 6 // 2
   3. 2 ** 2 ** 4
   4. ("na" * 8 + " ") * 2 + "Batman!"
   5. 1 + 2 ** 3 / 4 * 5 - (6 % 7)

3B - Program Execution and Return Values

3. For each of the following, say whether it is a statement or an expression:

   1. a = 4
   2. a + 4
   3. int(6.4) + 2

4. Suppose we run the following program, and the user types 6 and presses enter. What happens?

   user_num = input("Enter a number: ")
   result = 5 % (3 ** (user_num // 4))

5. Suppose we run the following program, and the user types 6 and presses enter. What value gets stored in result?

   user_num = int(input("Enter a number: "))
   result = 5 % (3 ** (user_num // 4))

6. What does the following expression evaluate to? float(str(int(2.6 / 2))*2)

Problems

1. Write a program that prompts the user for three numbers in a row, then prints the sum of all three numbers. The program should work if the user enters decimal numbers, but can throw an error if the user enters something that isn’t a number. An example run of the program might look like this, where the numbers after each prompt are typed by the user:

Enter the first number: 4
Enter the second number: 2.4
Enter the third number: 8.6
Your numbers total 15.0

2. Write a program to help a user calculate percentages. First prompt the user for an amount, then prompt the user for a percentage. Finally, print the percentage of the amount. The amounts and percents should handle floating-point values, but your program may throw an error if the user enters something that’s not a number. A sample run of the program might look like this:

   Enter an amount: 900
   Enter a percentage: 50.0
   50.0 percent of 900 is 450.0

3. Modify your program from #1 to print the full equation for the sum; for example, the last line of the example above would read

   4.0+2.4+8.6=15.0

   The catch: you have to print the equation without spaces between the numbers.