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: \\[ \begin{aligned} \text { if } \quad( \text { score } &=30) \\ \text { grade } &=' \mathrm{A}^{\prime} \end{aligned} \\] always evaluates to true. e. The expression: \\[ \left(\mathrm{ch}>=\mathrm{i} \mathrm{A}^{\prime} \& \& \mathrm{ch}<=\mathrm{r}^{\prime}\right) \\] evaluates to false if either \(\mathrm{ch}<\) ' \(\mathrm{A}\) ' or \(\mathrm{ch}>=\) ' \(\mathrm{Z}\) '. f. Suppose the input is \(5 .\) The output of the code: \\[ \begin{array}{l} \text { cin }>>\text { num; } \\ \text { if }(\text { num }>5) \end{array} \\] 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: False, e: False, f: True, g: True, h: False, i: False, j: True.

Step-by-step solution

Evaluate Statement a

The statement is: "The result of a logical expression cannot be assigned to an int variable." In C++, a logical expression results in either 'true' (1) or 'false' (0), which are both integer values. Thus, you can assign a logical expression to an int variable. This statement is False.

Evaluate Statement b

The statement is: "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." Placing a semicolon right after the condition in an if statement makes it an empty statement, which means it executes nothing when the condition is true. It does not mean the condition is always true, just that the program will execute the next statement in sequence regardless of the condition's truth. This statement is False.

Evaluate Statement c

The statement is: "Every if statement must have a corresponding else." In C++, an if statement does not need to have a corresponding else statement. The else part is optional. This statement is False.

Evaluate Statement d

The statement is: "The expression in the if statement: \( \text{ if } ( \text{ score } =30) \text{ grade } =' \mathrm{A} \) always evaluates to true." The statement is incorrect because the expression is an assignment \(\operatorname{score} = 30\), not a conditional \(\operatorname{==}\). It will assign 30 to score and then evaluate if 30 is non-zero, so it acts like it evaluates to true due to the assignment. This statement is False for conditional intent.

Evaluate Statement e

The statement is: "The expression: \(\mathrm{ch}>=\mathrm{A}\ &&\ \mathrm{ch}<=\mathrm{Z}\) evaluates to false if either \(\mathrm{ch}<\mathrm{A}\) or \(\mathrm{ch}>\mathrm{Z}\)." This statement means it's true if between A and Z, inclusive, otherwise false. The expression evaluates to false if either condition outside the range is true. This statement is False (based on OR condition description).

Evaluate Statement f

The statement is: "Suppose the input is 5. The output of the code: \[\text{cin }>>\text{ num;}\]\[\text{if }(\text{ num } >5)\]cout \(<<\) num; num \(=0\)else cout \(<<\) "Num is zero" \(<<\) \text{endl } is: Num is zero." Since 5 is not greater than 5, the code correctly outputs 'Num is zero'. This statement is True.

Evaluate Statement g

The statement is: "The expression in a switch statement should evaluate to a value of the simple data type." In C++, the expression in a switch statement should indeed evaluate to an integer or enumeration constant expression. This statement is True.

Evaluate Statement h

The statement is: "The expression !\((x>0)\) is true only if \(x\) is a negative number." The expression \(x > 0\) is true only for positive numbers. The negation \(!)\) makes it true for zero and negative numbers. Thus, it is true for \(x\leq 0\). This statement is False.

Evaluate Statement i

The statement is: "In C++, both \(!\) and \(!=\) are logical operators." The operator \(!\) is a logical NOT operator, while \(!=\) is an equality operator, checking if two values are not equal. This statement is False.

Evaluate Statement j

The statement is: "The order in which statements execute in a program is called the flow of control." This is a correct definition. This statement is True.

Key concepts

Logical Expressions

Logical expressions in C++ are crucial for decision making. These expressions evaluate to either `true` or `false`. They typically use relational and logical operators like `==`, `!=`, `&&`, and `||`. For instance, comparing two integers with `a == b` results in a boolean value. However, it's important to remember that in C++, `true` is represented by the integer `1` and `false` by `0`. Therefore, logical expressions can be assigned to an integer variable without any issue. This characteristic enables flexible control in programming, allowing integers to store boolean results for further processing. Understanding logical expressions' behavior is vital for writing effective conditional statements.

One-way Selection

One-way selection in C++ is implemented using `if` statements. It allows the program to decide whether to execute a block of code based on a condition. The basic syntax is `if (condition) { /* code to be executed if condition is true */ }`. If the condition evaluates to true, the code runs; otherwise, it's skipped. A common mistake in one-way selection is placing a semicolon right after the condition in an `if` statement. This semicolon turns the intended conditional block into an empty statement, resulting in unintentional behavior as the program continues executing subsequent statements regardless of the condition. It's important to ensure correct syntax to avoid logic errors.

Switch Statement

A `switch` statement offers an alternative to multiple `if` statements. It's used to execute different parts of code based on the value of a particular expression. The expression used in a `switch` statement should be of a simple data type, such as `int` or `char`. Each `case` within the switch represents a potential value of the expression and is followed by a block of code to execute if the expression matches. Remember to use `break` to prevent fall-through, where execution continues into the next case. The `default` case can handle any expressions that don't match any other case, providing comprehensive control of flow within decision-making structures.

Flow of Control

In programming, the flow of control determines the order in which statements are executed in a program. This involves directing the program's execution sequence using constructs like loops, conditionals, and functions. Understanding flow of control is essential for writing efficient and logical code. By controlling the flow, developers can manage how the program responds to different inputs and scenarios. It includes using `if` and `else` for branching, loops like `for` and `while` for iteration, and constructs like `switch` for multi-way branching. Mastering these constructs allows programmers to design programs that react dynamically and execute intended operations correctly.