Question

include using namespace std; const int NUM = 10; const double X = 20.5; int main() { in… # What is printed by the following program? Suppose the input is: 20 15 #include using namespace std; const int NUM = 10; const double X = 20.5; int main() { int a, b; double z; char grade; a = 25; cout << "a = " << a << endl; cout << "Enter two integers: "; cin >> a >> b; cout << endl; cout << "The numbers you entered are " << a << " and " << b << endl; z = X + 2 * a - b; cout << "z = " << z << endl; grade = 'A'; cout << "Your grade is " << grade << endl; a = 2 * NUM + z; cout << "The value of a = " << a << endl; return 0; }

Short answer

It will print: a = 25 Enter two integers: The numbers you entered are 20 and 15 z = 45.5 Your grade is A The value of a = 65

Step-by-step solution

Initialize and Print Initial Value of 'a'

When the program starts, the integer 'a' is immediately assigned the value 25. The value of 'a' is then printed using the command `cout << "a = " << a << endl;`. Thus, the first output line will be `a = 25`.

Prompt for Input of Two Integers

The program then prompts the user to enter two integers with the message `Enter two integers: `. When the user inputs `20 15`, these values are read by using `cin >> a >> b;` where `a` is set to 20 and `b` to 15. The program then confirms the input with the message `The numbers you entered are 20 and 15`.

Calculate and Output Variable 'z'

The program calculates 'z' using the formula `z = X + 2 * a - b;`. Here, `X = 20.5`, `a = 20`, and `b = 15`. Plug these into the formula:\[ z = 20.5 + 2 \times 20 - 15 = 45.5 \]The program outputs `z = 45.5`.

Output Grade

The character variable `grade` is assigned the value 'A'. The program outputs `Your grade is A`.

Calculate New Value of 'a' and Output

Finally, 'a' is reassigned with the result of the expression `a = 2 * NUM + z;`. With `NUM = 10` and the previously calculated `z = 45.5`, the expression becomes:\[ a = 2 \times 10 + 45.5 = 65.5 \]Since 'a' is an integer, it will be truncated to `65`. The program outputs `The value of a = 65`.

Key concepts

Variables and Data Types

In C++ programming, variables are used as storage locations to hold data that your program may manipulate. Each variable in C++ has a specific data type, which determines the size and layout of the variable's memory. It also defines the possible values that can be stored and the operations that can be performed on the values.

Common data types include:

• int: Used for integers. For example, variable `a` in the code is of type `int` and can hold whole numbers like 25, 20, or 15.
• double: Used for floating-point numbers. Variable `X` is a `double` that can store decimal values like 20.5.
• char: Used for single characters. The variable `grade` stores the character `'A'`.

Understanding these distinctions helps in selecting the appropriate data type for your variables, ensuring that they store data correctly and perform the expected operations without errors. Choosing the wrong data type might result in loss of information or errors in calculations. When you need precision with numbers involving decimals, use `double`. For most integer needs, `int` is appropriate.

Standard Input and Output

In C++, standard input and output operations are commonly performed using commands from the `iostream` library, which provides functionalities to read and write data to and from the console.

Here's how they work:

• `cin`: This is used to take input from the user. In the exercise, `cin >> a >> b;` reads two integers entered by the user from the keyboard and stores them in variables `a` and `b` respectively.
• `cout`: Utilized to output data to the console. For instance, `cout << "a = " << a << endl;` prints the value of `a`, along with a descriptive string, to the screen.

The use of `<<` and `>>` in `cout` and `cin` is analogous to showing data to and taking data from the user, respectively. The `endl` statement can be used to insert a new line in the output, making the display more readable.

Basic Arithmetic Operations

Arithmetic operations are fundamental to programming in C++. They allow you to perform calculations on variables and express logic within your code.

Some common operations include:

• Addition `+`: Combines values. For example, `X + 2 * a` adds the result of `2 * a` to `X`.
• Subtraction `-`: Finds the difference between values. The operation `X + 2 * a - b` subtracts `b` from `X + 2 * a`.
• Multiplication `*`: Computes the product of values. Here, `2 * a` multiplies the integer `a` by 2.
• Truncation (in implicit conversion): When a `double` result is assigned to an `int`, it loses its decimal portion. For example, `a = 2 * NUM + z;` results in a double, but once assigned to an integer variable `a`, the decimal part is removed, yielding 65 instead of 65.5.

Understanding how these basic arithmetic operations work and combining them effectively is crucial when creating complex calculations and algorithms in your programs. Proper usage ensures that your program performs accurately and as intended.