In this section, we will explore the fundamental concepts of variables and data types in ALGOL. Understanding these concepts is crucial as they form the building blocks for any program you write.

What is a Variable?

A variable in ALGOL is a symbolic name associated with a value and whose associated value may be changed. Variables are used to store data that can be manipulated by the program.

Declaring Variables

In ALGOL, variables must be declared before they are used. The declaration specifies the type of data the variable will hold. Here is the general syntax for declaring a variable:

<type> <variable_name>;

Example

integer x;
real y;
boolean flag;

In this example:

  • x is declared as an integer.
  • y is declared as a real number.
  • flag is declared as a boolean.

Data Types

ALGOL supports several data types, each serving a different purpose. The primary data types in ALGOL are:

  1. Integer: Used to store whole numbers.
  2. Real: Used to store floating-point numbers.
  3. Boolean: Used to store true or false values.
  4. Character: Used to store single characters.

Integer

The integer data type is used to store whole numbers without a fractional component.

integer age;
age := 25;

Real

The real data type is used to store numbers with a fractional component.

real temperature;
temperature := 36.6;

Boolean

The boolean data type is used to store logical values: true or false.

boolean isRaining;
isRaining := true;

Character

The character data type is used to store single characters.

character initial;
initial := 'A';

Basic Input and Output

To interact with the user, you need to understand how to perform basic input and output operations.

Input

To read input from the user, you can use the read statement.

integer number;
read(number);

Output

To display output to the user, you can use the print statement.

integer number;
number := 10;
print(number);

Practical Example

Let's put it all together in a simple program that reads an integer from the user, doubles it, and then prints the result.

begin
    integer number, result;
    
    print("Enter an integer: ");
    read(number);
    
    result := number * 2;
    
    print("The double of the entered integer is: ");
    print(result);
end

Explanation

  1. Variable Declaration: We declare two integer variables, number and result.
  2. Input: We prompt the user to enter an integer and read the input into the variable number.
  3. Processing: We calculate the double of the entered integer and store it in result.
  4. Output: We print the result.

Exercises

Exercise 1

Task: Write a program that reads a real number from the user, squares it, and prints the result.

Solution:

begin
    real number, result;
    
    print("Enter a real number: ");
    read(number);
    
    result := number * number;
    
    print("The square of the entered number is: ");
    print(result);
end

Exercise 2

Task: Write a program that reads a character from the user and prints its ASCII value.

Solution:

begin
    character ch;
    integer asciiValue;
    
    print("Enter a character: ");
    read(ch);
    
    asciiValue := ord(ch);
    
    print("The ASCII value of the entered character is: ");
    print(asciiValue);
end

Common Mistakes and Tips

  • Uninitialized Variables: Always initialize your variables before using them to avoid unexpected behavior.
  • Type Mismatch: Ensure that the data type of the variable matches the type of data you are assigning to it.
  • Read and Print Statements: Be careful with the syntax of read and print statements to avoid syntax errors.

Conclusion

In this section, we covered the basics of variables and data types in ALGOL. We learned how to declare variables, the different data types available, and how to perform basic input and output operations. These concepts are fundamental and will be used throughout your programming journey in ALGOL. In the next section, we will delve into operators and expressions, which will allow us to perform more complex computations.

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