Question

Mark the following statements as true or false. a. The result of a logical expression cannot be assigned to an int variable. b. In a one-way selection, if a semicolon is placed after the expression in an if statement, the expression in the if statement is always true. c. Every if statement must have a corresponding else. d. The expression in the if statement: if \(\quad(\text { score }=30)\) grade \(=' \mathrm{A}^{\prime}\) always evaluates to true. e. The expression: \((\mathrm{ch}>=\text { 'A ' } \& \& \mathrm{ch}<=\text { ' } \mathrm{Z}\) ') f. Suppose the input is \(5 .\) The output of the code: cin \(>>\) num; if \((\text { num }>5)\) cout \(<<\) num \(;\) num \(=0\); else cout \(<<\) "Num is zero" \(<<\) endl is: Num is zero g. The expression in a switch statement should evaluate to a value of the simple data type. h. The expression ! \((x>0)\) is true only if \(x\) is a negative number. i. \(\quad\) In \(C++,\) both \(!\) and \(!=\) are logical operators. j. The order in which statements execute in a program is called the flow of control.

Short answer

a. False, b. False, c. False, d. True, e. True, f. True, g. True, h. False, i. True, j. True.

Step-by-step solution

Statement a

The result of a logical expression could be either true or false, representing boolean values. In C++, true and false are internally represented by integers 1 and 0, so the result of a logical expression can be assigned to an int variable. **False**.

Statement b

In a one-way selection, placing a semicolon after the expression in an if statement effectively ends the conditional block. It does not affect the condition itself, but it makes the subsequent code outside the conditional block always execute, regardless of the expression's result. **False**.

Statement c

It is not necessary for every if statement to have a corresponding else statement. An if statement can exist without an else to handle cases where no alternative action is needed. **False**.

Statement d

The expression in the if statement is using an assignment (single `=`) instead of a comparison (double `==`). This means `score` will be assigned the value 30, and the grade assignment will always be executed. **True**.

Statement e

This expression checks if a character `ch` is between 'A' and 'Z' inclusive, effectively determining if it's an uppercase letter. This is a valid logical condition, so assuming ch is a character, it correctly evaluates the check. **True**.

Statement f

The provided code reads an integer and compares it to 5. Since the input is exactly 5, the condition `(num > 5)` evaluates to false, so the else block is executed, outputting "Num is zero". **True**.

Statement g

In a switch statement, the expression should yield a value of an integral or enumeration type, which are considered simple data types in C++. **True**.

Statement h

The expression `!(x>0)` is true only when `x` is not greater than 0, which encompasses both zero and negative numbers. Thus, the original statement is incorrect. **False**.

Statement i

In C++, `!` is the logical NOT operator, and `!=` is the inequality comparison operator. Both are operators, but they serve different purposes. **True**.

Statement j

The order in which statements are executed in a program indeed constitutes the flow of control, which is a fundamental concept in programming execution. **True**.

Key concepts

Logical Expressions

Logical expressions in C++ are used to perform logical (Boolean) operations. These operations result in a Boolean value of either true or false. Common logical operators include AND (&&), OR (||), and NOT (!). These operators help in forming logical expressions that control the flow of a program through conditional statements.
In C++, logical expressions are often used within if statements and loops to determine which blocks of code should execute. Even though the result of a logical expression is a Boolean, it can be assigned to an int variable, where true is represented by 1 and false by 0.
Logical expressions are especially important for evaluating conditions because they decide the path that execution will take. For example, a logical expression like (a > b) will evaluate to true if a is greater than b, consequently executing a certain block of code.

If Statements

If statements in C++ are the cornerstone for implementing conditional logic. These statements allow a program to make decisions based on certain conditions. The basic syntax of an if statement follows "if (condition) { // code block }". If the condition within the parentheses is true, the code block within the curly braces executes.
There are different forms of if statements:

• One-way selection: Here, the code block executes only if the condition is true. If false, the program continues sequentially without executing the inside block.
• Two-way selection: Also known as if-else, where an else block executes if the condition is false, providing an alternative path.
• Nested if: Involves placing an if statement inside another if statement, allowing for complex decision-making.

An important aspect of using if statements is ensuring the correct placement of semicolons. A misplaced semicolon, like after "if (condition);", can inadvertently terminate the conditional block, leading to logical errors.

Switch Statements

Switch statements in C++ offer a way to select between multiple paths of execution. They evaluate a single expression and execute the block of code that matches the corresponding case value. This is particularly useful when a variable is compared against numerous potential values.
The basic structure of a switch statement is: "switch(expression) { case value1: // code block break; case value2: // code block break; ... default: // default block }". The expression in a switch must result in an integral or enumeration type.
Each case ends with a break statement to prevent fall-through, which occurs when multiple case blocks execute one after another if break is omitted. Switch statements are preferred over multiple if-else blocks when the same variable is tested against several constant values, improving code readability and execution efficiency.

Flow of Control

Flow of control refers to the order in which the instructions of a program are executed. In C++, this flow is primarily controlled by construct structures such as loops and decision-making statements.
Key constructs that influence flow of control include:

• Sequential: The default mode, where code is executed one statement after another.
• Selection: Controlled by if statements and switch statements, where code branches based on logical conditions.
• Iteration: Managed by loops like for, while, and do-while, allowing code to execute repeatedly based on conditions.

Flow of control determines how a program reacts to inputs and events, enabling it to perform tasks ranging from basic to complex based on conditional logic.