Question

Suppose \(x\) and \(y\) are variables each of which contains a number. Write a code fragment that sets \(y\) to \(x\) if \(x\) is positive and to 0 otherwise.

Short answer

Set \( y = x \) if \( x > 0 \), else set \( y = 0 \).

Step-by-step solution

Analyze the Problem

We need to set the value of the variable \( y \) based on the condition of the value of \( x \). If \( x \) is positive, \( y \) should equal \( x \). If \( x \) is not positive (i.e., negative or zero), then \( y \) should be set to 0.

Select Code Language

Decide the programming language in which you will write the code. For this example, let's use Python.

Write the Code Fragment

Now, we'll write a simple conditional structure in Python to meet the problem's requirements. Use an if-else statement to check the condition. ```python if x > 0: y = x else: y = 0 ```

Explanation of the Code

In the given code, we first check whether \( x \) is greater than 0 using the statement `if x > 0`. If this condition is true, \( y \) is set to \( x \). Otherwise, as handled by the `else` block, \( y \) is set to 0.

Key concepts

Conditional Statements in Python

Conditional statements in Python are decision-making tools that allow a program to choose between different paths based on the evaluation of certain conditions. These are very intuitive and are mostly used to execute certain parts of the code only when particular conditions are met. The most basic form of a conditional statement in Python is the `if` statement. In the context of the provided code, the `if` statement checks if the value of the variable \(x\) is greater than zero.

• If this condition is true, the code within the `if` block is executed. This means that \(y\) is set to the value of \(x\).
• If the condition is false, the code within the `else` block is carried out, which sets \(y\) to 0.

Understanding the flow of conditional statements like `if` and `else` helps you direct the control flow of your programs, enabling them to make intelligent decisions automatically. In larger programs, you might use more complex structures like `elif` which represents "else if," allowing further checks after an initial `if` statement.

Working with Variables

Variables in Python are symbolic names associated with values. They act like containers that hold data and can be manipulated during the execution of a program. In Python, you do not need to declare a variable with a specific type, as Python is dynamically typed. This means that it assigns data types during runtime automatically.In the provided exercise, there are two variables, \(x\) and \(y\). Both are placeholders for numeric values. Initially, \(x\) contains the number used to determine the value of \(y\). Based on the conditional statement in the code, \(y\) will be reassigned to either the value of \(x\) or zero.

• Variables provide a way to hold data, making your program flexible and dynamic.
• They can be manipulated and changed during the program, leading to different outcomes based on logic programmed.

Remember, when creating variables, give them meaningful names so their purpose is immediately clear within the context of your code.

Understanding Control Structures

Control structures are fundamental components in programming that determine the control flow—the sequence in which individual statements, instructions, or function calls are executed or evaluated. In Python, the most basic control structures are sequential, selection (conditional statements), and repetition (loops). The code snippet in the original exercise uses the selection control structure, specifically through the `if-else` statement. This allows the program to decide which path to take when different conditions are met or not met.

• Selection: Use conditional statements to decide whether a block of code will be executed.
• Sequential: The standard control structure where statements are executed one after another in order.
• Repetition: Repeating a set of statements multiple times typically using loops like `for` or `while`.

By mastering control structures, you can craft conditions that handle numerous scenarios automatically, thus making your programs more efficient and adaptable.