Question

Suppose that the input is \(25361816-1 .\) What is the output of the following code? int num; int sum; \(\operatorname{cin}>>\operatorname{sum}\) num \(=\) sum;

Short answer

The output of the code is 25361815.

Step-by-step solution

Analyze the Code

The code consists of a variable declaration, an input operation, and an assignment statement. The variable `sum` is supposed to take input from the user using `cin`, and then `num` is assigned the value of `sum`. Hence, the output of the code will be the value assigned to `num`, which is the same as the input given to `sum`.

Determine the Input Value

According to the problem statement, the input to the `sum` variable is given as `25361816-1`. This operation should be evaluated before being used as input.

Perform the Subtraction

Calculate the expression `25361816 - 1` to determine the exact input value. The result of this subtraction operation is `25361815`.

Assign the Value to 'num'

The code assigns the computed value of `sum`, which is `25361815`, to the variable `num`. Hence, `num` will hold the value `25361815`.

Key concepts

Variable Declaration

In C++, before using a variable, we must declare it. This tells the compiler to reserve space in memory for the variable and define what kind of data it will hold. For instance, the code `int num;` and `int sum;` are examples of variable declarations. The `int` keyword specifies that these variables are of type integer, meaning they can hold whole numbers.

Once a variable is declared, you can use it in your code. Generally, variable names should be descriptive of their purpose. This helps in understanding the code better and maintaining it in the future. Proper variable declaration is crucial as it prevents errors when the program is executed.

Input Operation

Input operations allow programs to receive data from external sources, typically from the user or other input devices. In C++, this is often done using the `cin` keyword in combination with the extraction operator `>>`. For example, `cin >> sum;` reads a value from the standard input and stores it in the variable `sum`.

It's important to ensure that the input is of the correct type as expected by the program. If the user inputs a data type not compatible with the variable, it may cause unexpected behavior or an error. Input operations connect programs with real-world data, making them dynamic and interactive.

Assignment Statement

An assignment statement in C++ assigns the value of an expression to a variable. This is done using the assignment operator `=`. For example, `num = sum;` assigns the current value of `sum` to the variable `num`.

Assignment statements are fundamental in programming because they control how data is stored, changed, and moved within a program. The assignment operator always evaluates the right-hand side (RHS) of the assignment first and then stores this evaluated result in the variable on the left-hand side (LHS). This means whatever value `sum` holds after being input becomes the value of `num` after the assignment.

Expression Evaluation

Expression evaluation refers to the process of computing the result of expressions in code, such as mathematical operations. In the exercise given, an expression `25361816 - 1` needed evaluation. The subtraction operation is performed first, resulting in `25361815` before this value is used within the program.

In C++, the order of operations follows mathematical conventions; thus, expressions are evaluated according to operator precedence and associativity rules. Ensuring expressions are correctly evaluated is crucial for accurate program output. The result of this evaluation frequently determines the flow of the program and affects the values assigned to the variables.