In this section, we will cover the basics of input and output (I/O) operations in Fortran. Understanding how to read data from the user and display results is fundamental for any programming language. Fortran provides several ways to handle I/O operations, and we will explore the most commonly used methods.

1. READ Statement: Used to read input from the user or a file.
2. WRITE Statement: Used to write output to the screen or a file.
3. FORMAT Statement: Used to control the layout of the input and output.

The READ statement is used to read data from the standard input (usually the keyboard) or from a file. The basic syntax is:

• The first asterisk * indicates the standard input.
• The second asterisk * indicates list-directed input, which means the input format is determined by the data type of the variables.

• PRINT *, 'Enter your age:' displays a prompt to the user.
• READ(*, *) age reads an integer value from the user and stores it in the variable age.
• PRINT *, 'Enter your height in meters:' displays another prompt.
• READ(*, *) height reads a real number from the user and stores it in the variable height.
• Finally, the program prints the collected information.

The WRITE statement is used to write data to the standard output (usually the screen) or to a file. The basic syntax is:

• The first asterisk * indicates the standard output.
• The second asterisk * indicates list-directed output, which means the output format is determined by the data type of the variables.

• age = 25 assigns the value 25 to the variable age.
• height = 1.75 assigns the value 1.75 to the variable height.
• WRITE(*, *) 'Age:', age writes the string 'Age:' followed by the value of age to the standard output.
• WRITE(*, *) 'Height:', height writes the string 'Height:' followed by the value of height to the standard output.

The FORMAT statement is used to control the layout of the input and output. It allows you to specify the exact format in which data should be read or written.

• WRITE(*, '(A, I3)') 'Age:', age writes the string 'Age:' followed by the integer age in a field of width 3.
• WRITE(*, '(A, F5.2)') 'Height:', height writes the string 'Height:' followed by the real number height in a field of width 5 with 2 decimal places.

Write a program that asks the user for their name and age, then prints a greeting message.

Solution

Write a program that reads a real number from the user and prints it with 3 decimal places.

Solution

• Forgetting to declare variables: Always declare your variables with the appropriate data type.
• Incorrect format specifiers: Ensure that the format specifiers in the FORMAT statement match the data types of the variables.
• Using uninitialized variables: Make sure to initialize your variables before using them in I/O operations.

In this section, we covered the basics of input and output operations in Fortran using the READ and WRITE statements. We also explored how to control the layout of the input and output using the FORMAT statement. These fundamental skills are essential for interacting with users and handling data in your Fortran programs. In the next section, we will delve into control structures, starting with If statements.