Section 1.13 - IT 140_ Introduction to Scripting _ zyBooks

 Students: Section 1.13 is a part of 1 assignment: 1-3 zyBooks Participation Activities Includes: PA 1.13 Variables and assignments Remembering a value Here's a variation on a common school child riddle. CHALLENGE ACTIVITY 1.13.1: People on bus. For each step, keep track of the current number of people by typing in the num_people box (it's editable). 553398.3976864.qx3zqy7 By the way, the real riddle's ending question is actually, "What is the bus driver's name?" The subject usually says, "How should I know?" The riddler then says, "I started with YOU are driving a bus." The box above serves the same purpose as a variable in a program, introduced below. Variables and assignments In a program, a variable is a named item, such as x or num_people, used to hold a value. An assignment statement assigns a variable with a value, such as x = 5. That statement means x is assigned with 5, and x keeps that value during subsequent statements, until x is assigned again. An assignment statement's left side must be a variable. The right side can be an expression, so a statement may be x = 5, y = x, or z = x + 2. The 5, x, and x + 2 are each an expression that evaluates to a value. PARTICIPATION ACTIVITY 1.13.1: Variables and assignments. = is not equals In programming, = is an assignment of a left-side variable with a right-side value. = is NOT equality as in mathematics. Thus, x = 5 is read as "x is assigned with 5," and not as "x equals 5." When one sees x = 5, one might think of a value being put into a box. PARTICIPATION ACTIVITY 1.13.2: Valid assignment statements. Indicate which assignment statements are valid. 1) x = 1 Valid Invalid 2) x = y Valid Invalid 3) x = y + 2 Valid Invalid 4) x + 1 = 3 Valid Invalid Start You are driving a bus. The bus starts with 5 people. num_people: 5 2 3 4 5 Check Next Feedback? x = 5 x y y = x z = x + 2 x = 3 z x + y = 5 x * y = 6 Algebra x = 2 y = 3 Programming 5 5 7 3 Captions  Feedback? 1 Start 2x speed

5) x + y = y + x Valid Invalid PARTICIPATION ACTIVITY 1.13.3: Variables and assignment statements. Given variables x, y, and z. 1) x = 9 y = x + 1 What is y? 2) x = 9 y = x + 1 What is x? 3) x = 9 y = x + 1 x = 5 What is y? PARTICIPATION ACTIVITY 1.13.4: Trace the variable value. Select the correct value for x, y, and z after the following statements execute. Assignments with variable on left and right Because in programming = means assignment, a variable may appear on both the left and right as in x = x + 1. If x was originally 6, x is assigned with 6 + 1, or 7. The statement overwrites the original 6 in x. Increasing a variable's value by 1, as in x = x + 1, is common and known as incrementing the variable. PARTICIPATION ACTIVITY 1.13.5: A variable may appear on the left and right of an assignment statement. PARTICIPATION ACTIVITY 1.13.6: Variable on both sides. Feedback? Check Show answer Check Show answer Check Show answer Feedback? Start int x = 2; int y = 7; int z = 8; x = 8; y = 5; z = 9; x = 1; x is 2 8 1 y is 0 7 5 z is 3 8 9 2 3 4 Check Next Feedback? Put "A person with measles may cause " to output x = 1 x = x * 20 x = x * 20 Put x to output Put "people to be infected in two weeks." to output x A person with measles may cause Put newline to output 400 people to be infected in two weeks. 1 20 400 1. A variable may appear on both sides of an assignment statement. After x = 1, then x = x * 20 assigns x with 1 * 20 or 20, overwriting x's previous 1. 2. Another x = x * 20 assigns x with 20 * 20 or 400, which overwrites x's previous 20. 3. Only the latest value is held in x. Captions  Feedback? 1 Start 2x speed

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