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Chapter 4: Problem 13

How does a dual alternative decision structure work?

Short Answer

Expert verified
Answer: A dual-alternative decision structure, also known as the if-else statement, is a basic concept in programming used to determine which set of actions should be taken based on whether a condition is true or false. It consists of a condition and two blocks of code: one to execute if the condition is true and another if the condition is false. The flow of control in the program first evaluates the condition, and if it is true, it executes the block of code following the if statement. If the condition is false, it executes the block of code following the else statement. This structure helps in making a program more flexible and adaptive to different situations by controlling the flow of the program and enabling it to make decisions based on logical conditions.

Step by step solution

01

Understand the structure of a dual-alternative decision

A dual-alternative decision structure, or an if-else statement, consists of: - a condition (a statement that evaluates to either true or false) - a block of code (instructions to perform) if the condition is true - another block of code if the condition is false The general format looks like this: ``` if (condition) { // Code to execute if the condition is true } else { // Code to execute if the condition is false } ```
02

Examine a specific example

Consider an example of a program that checks if a student has an average score above a passing threshold (let's say the passing threshold is 70). ```Python average_score = 85 if (average_score >= 70): print("You passed!") else: print("You failed!") ```
03

Understand the flow of control

To understand how the dual-alternative decision structure works, let's break down the flow of control in the example: 1. The program evaluates the condition: (average_score >= 70). Since the value of average_score is 85, this condition is true. 2. Because the condition is true, the program executes the block of code following the if statement: print("You passed!"). 3. The else block of code is skipped, as the condition of the if statement is true. 4. The flow of control continues after the else block. If the average_score was below 70, the condition would be false, and the program would execute the block of code following the else statement.
04

Use cases for a dual-alternative decision structure

Dual-alternative decision structures are widely used in various programming scenarios where the program needs to perform different actions based on different conditions. Some common use cases include: - Checking user input (whether it is valid or not) - Comparing values (for sorting or decision making) - Testing conditions for loops The main goal of using a dual-alternative decision structure is to make a program more flexible and adaptive to different situations. It helps control the flow of a program and enables it to make decisions based on logical conditions.

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Most popular questions from this chapter

The following truth table shows various combinations of the values true and false connected by a logical operator. Complete the table by circling T or \(\mathrm{F}\) to indicate whether the result of such a combination is true or false. $$\begin{array}{lcc} \text { Logical Expression } & \text { Result (circle T or F) } \\ \text { True AND False } & \mathrm{T} & \mathrm{F} \\ \text { True AND True } & \mathrm{T} & \mathrm{F} \\ \text { False AND True } & \mathrm{T} & \mathrm{F} \\ \text { False AND False } & \mathrm{T} & \mathrm{F} \\ \text { True OR False } & \mathrm{T} & \mathrm{F} \\ \text { True or True } & \mathrm{T} & \mathrm{F} \\ \text { False or True } & \mathrm{T} & \mathrm{F} \\ \text { False or False } & \mathrm{T} & \mathrm{F} \\ \text { Not True } & \mathrm{T} & \mathrm{F} \\ \text { NOT False } & \mathrm{T} & \mathrm{F} \end{array}$$

If the following pseudocode were an actual program, what would it display? Declare String s1 = "New York" Declare String s2 = "Boston" If s1 > s2 Then Display s2 Display s1 Else Display s1 Display s2 End If

Convert the following pseudocode to an If-Then-Else If statement: If number == 1 Then Display "One" Else If number == 2 Then Display "Two" Else If number == 3 Then Display "Three" Else Display "Unknown" End If End If End If

What values can you store in a Boolean variable?

What is a single alternative decision structure?
See all solutions

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