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

The program prints: 25, the integers 20 and 15, z as 45.5, grade A, and a as 65.

Step-by-step solution

Initial Value of 'a'

The program starts by declaring and initializing the integer variable 'a' to 25. It prints this value immediately. Output: ``` a = 25 ```

User Input for 'a' and 'b'

The program asks the user to input two integer values. According to the exercise, the given input values are 20 and 15, which are then stored in 'a' and 'b', respectively.

Output of Entered Numbers

The program prints the values entered by the user. In this case, it will output the values 20 and 15 for 'a' and 'b'. Output: ``` The numbers you entered are 20 and 15 ```

Calculation of 'z'

The program calculates the variable 'z' using the formula: \[ z = X + 2 \cdot a - b \]Substitute the values of 'X', 'a', and 'b':\[ z = 20.5 + 2 \cdot 20 - 15 \]\[ z = 20.5 + 40 - 15 \]\[ z = 45.5 \]The program then prints this value of 'z'.Output:```z = 45.5```

Output of 'grade'

The character variable 'grade' is initialized to 'A' and printed. Output: ``` Your grade is A ```

Calculation of New Value for 'a'

Finally, 'a' is recalculated using the formula:\[ a = 2 \cdot NUM + z \]Substitute the values of 'NUM' and 'z':\[ a = 2 \cdot 10 + 45.5 \]\[ a = 20 + 45.5 \]\[ a = 65.5 \]Since 'a' is an integer, the decimal part is truncated, leaving 'a' as 65. The program prints this final value of 'a'.Output:```The value of a = 65```

Key concepts

C++ Input/Output

In C++, input and output operations are performed using streams. To handle input and output, you need to include the `` header file, which provides facilities for manipulating streams. The Standard Library's `cin` and `cout` objects are used for reading from standard input (usually the keyboard) and writing to standard output (usually the console), respectively.

`cin` is used to get user input. In the provided exercise, `cin >> a >> b;` reads two integers entered by the user and stores them in the variables 'a' and 'b'. Always remember to prompt the user for input with a message like `"Enter two integers: "` so users know what to do next.

`cout` is used to display output. You can use it to print messages, variables, and expressions. For example, `cout << "a = " << a << endl;` prints the initial value of 'a'. Each part between the `<<` operators is sent to the standard output. Always include `endl` to move to the next line, making outputs clean and readable.

Variable Initialization

In C++, variables must be declared and can be initialized before use. A declaration tells the compiler the variable's data type and optionally assigns an initial value. In the exercise, variables are declared as different data types: `int a, b;` and `double z;`.

Initialization assigns an initial value to a variable when it is created. For example, `a = 25;` assigns the integer 25 to the variable 'a' right after it is declared. Initializing variables is crucial as it sets a starting point for their values, avoiding undefined behavior during arithmetic operations or output.

Constants like `const int NUM = 10;` are initialized once and cannot be changed throughout the program. Using constants improves code readability and reliability, especially when the value is used in multiple places.

Arithmetic Operations

Arithmetic operations in C++ are fundamental for performing calculations in programs. The basic operations include addition, subtraction, multiplication, and division, represented by the operators `+`, `-`, `*`, and `/` respectively.

In the exercise, the expression for calculating 'z' is `z = X + 2 * a - b;`, demonstrating these operations. Initially, 'a' and 'b' are read from the user input, and then used along with the constant 'X' to compute 'z'. The calculation steps are:

• Compute `2 * a`, which is the product of 2 and the value stored in 'a'.
• Add the result to 'X'.
• Subtract 'b' from this result.

These steps follow the usual rules of arithmetic operations, respecting the order of precedence: multiplication and division before addition and subtraction.
Another operation modifies 'a' with `a = 2 * NUM + z;`, showing a combination of multiplication and addition.

Character and Integer Data Types

C++ has a variety of data types to store different kinds of data. Two essential types are character (`char`) and integer (`int`).

A `char` variable stores a single character. In the exercise, `char grade = 'A';` assigns the letter 'A' to the variable 'grade'. Characters are enclosed in single quotes. They use 1 byte of memory and can store values from -128 to 127 or 0 to 255, depending on whether signed or unsigned.

An `int` variable holds integer values. They are often used because they store numbers without decimal places efficiently. In the provided program, integers 'a' and 'b' are manipulated with arithmetic operations. The output demonstrates an integer truncating any fraction to retain only the whole number, which is crucial when integer types mix with floating-point calculations.

Understanding these data types helps predict and control how data is processed and stored within a program, critical for producing correct results.