--- title: "Formatted and unformatted I/O in FORTRAN" subject: "Computer Programming" chapter: 11 key: "semester_1/computer_programming:fortran-formatted-unformatted-io" source: https://www.bctengineer.com/q/semester_1/computer_programming/fortran-formatted-unformatted-io site: BCT Engineering --- # Formatted and unformatted I/O in FORTRAN Computer Programming · Chapter 11: Programming Language: FORTRAN - Asked in: 2071 Shrawan, 8 marks - Video: [FORTRAN Formatted Input Output](https://www.youtube.com/watch?v=R91Ojgm18uw) — Sanjay Adhau - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_1/computer_programming/fortran-formatted-unformatted-io - Whole chapter: https://www.bctengineer.com/md/semester_1/computer_programming/chapter-11 ## Question What do you mean by formatted and unformatted input/output statements in Fortran and also give suitable example which explain the concept of Formatted I/O? ## Short answer Formatted I/O uses a FORMAT statement with edit descriptors (e.g., 2I4) to control output; example: WRITE(*,20) L,B. Unformatted I/O uses READ * (list‑directed) or binary file I/O without a format. ## Answer #### Formatted input/output In formatted I/O the programmer controls the exact form of the data by a **FORMAT** statement (edit descriptors) referred to by a label in `READ` or `WRITE`. Data are converted between their internal form and readable text. Syntax: `WRITE(unit, label) list` and `label FORMAT(descriptors)` Common descriptors: `Iw` integer, `Fw.d` real with d decimals, `Ew.d` exponent form, `Aw` character, `nX` n blanks, `/` new line, and quoted text. #### Unformatted input/output - **List-directed (free format):** `READ *, A, B` and `PRINT *, A, B` (or `READ(*,*)`) do not use a FORMAT. The computer decides the layout, with values separated by blanks or commas. Many textbooks call this unformatted I/O. - In the strict sense, **unformatted I/O** means writing and reading the internal binary form to a file (`OPEN(..., FORM='UNFORMATTED')`, then `WRITE(10) list`). It is fast, with no conversion, but not readable by people. #### Example of formatted I/O ```fortran PROGRAM RECT INTEGER L, B REAL A READ(*,10) L, B A = L * B WRITE(*,20) L, B, A 10 FORMAT(2I4) 20 FORMAT(' LENGTH =', I4, ' BREADTH =', I4, /, ' AREA =', F8.2) STOP END ``` For input ` 12 5` the output is ```text LENGTH = 12 BREADTH = 5 AREA = 60.00 ``` `2I4` reads two integers of width 4, `F8.2` prints a real in 8 columns with 2 decimals, and `/` starts a new line. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What controls the exact form of data in formatted I/O? A. A FORMAT statement with edit descriptors B. The compiler C. The * unit D. The OPEN statement only Answer: A. A label in READ/WRITE refers to a FORMAT statement that describes the layout. (Key point: Formatted I/O) 2. What is READ *, A, B called? A. Formatted with F descriptors B. List-directed (free-format) input C. Binary input D. An error Answer: B. No FORMAT is used; the computer decides the layout. Many textbooks call this unformatted I/O. (Key point: List-directed) 3. In the strict sense, what is unformatted I/O? A. Reading and writing the internal binary form to a file without conversion B. Printing text with no spaces C. Using I descriptors only D. Using READ * Answer: A. FORM='UNFORMATTED' files hold binary data: fast but not readable by people. (Key point: Strict unformatted) 4. In the example, what do 2I4 and F8.2 do? A. 2I4 reads two integers of width 4; F8.2 prints a real in 8 columns with 2 decimals B. 2I4 prints 2 reals; F8.2 reads integers C. Both print text D. 2I4 prints 4 integers Answer: A. I4 is an integer of width 4, repeated twice; F8.2 means width 8 with 2 decimals. 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