1. Chapter 5 Basic I/O Concepts Dr. Ali Can Takinacı İstanbul Technical University Faculty of Naval Architecture and Ocean Engineering İstanbul - Turkey Tel: +90 (212 285 6519) Fax: +90 (212 285 6508) E-mail: takinaci@itu.edu.tr

2. Basic I/O Concepts In the previous chapters, we have read values into and written them out of our programs using list-directed READ and WR IT E statements. List-directed I/O statements are said to be in free format. Free format is specified by the second asterisk in the READ( *,*) and WRITE (*, *) statements. As we saw, the results of writing out data in free format are not always pretty. There are often a large number of extra spaces in the output. In this chapter, we will learn how to write out data by using formats that specify the exact way in which the numbers should be printed out. Basic I/O Concepts

3. FORMATS AND FORMATTED WRITE STATEMENTS A format may be used to specify the exact manner in which variables are to be printed out by a program. In general, a format can specify both the horizontal and the vertical position of the variables on the paper, and also the number of significant digits to be printed out. A typical formatted WRITE statement for an integer i and a real variable resul t is shown below: © 2010, Dr. ALİ CAN TAKİNACI Slide No: 3 Label of statementformat descriptors Basic I/O Concepts

4. In addition to FORM AT statements, formats may be specified in character constants or variables. If a character constant or variable is used to contain the format, then the constant or the name of the variable appears within the parentheses in the WRITE statement. For example, the following three WRITE statements are equivalent: Basic I/O Concepts

5. FORMAT DESCRIPTORS There are many different format descriptors. They fall into four basic categories: 1. Format descriptors that describe the vertical position of a line of text. 2. Format descriptors that describe the horizontal position of data in a line. 3. Format descriptors that describe the output format of a particular value. 4. Format descriptors that control the repetition of portions of a format. Basic I/O Concepts

6. Real Output-The F Descriptor One format descriptor used to describe the display format of real data is the F descriptor. It has the form rFw.d Real values are printed right justified within their fields. If necessary, the number will be rounded off before it is displayed Basic I/O Concepts

7. Real Output-The E Descriptor Real data can also be printed in exponential notation using the E descriptor. Scientific notation is a popular way for scientists and engineers to display very large or very small numbers. It has the form rEw.d For example, suppose that we want to print out a variable in the E format with 4 significant digits of accuracy. Then a field width of 11 characters is required, as shown below: 1 for the sign of the mantissa, 2 for the zero and decimal point, 4 for the actual mantissa, 1 for the E, 1 for the sign of the exponent, and 2 for the exponent itself. © 2010, Dr. ALİ CAN TAKİNACI Slide No: 7 the width of an E format descriptor field Basic I/O Concepts

8. Notice that the fourth field is all asterisks, since the format descriptor does not satisfy Equation w >=d+7 © 2010, Dr. ALİ CAN TAKİNACI Slide No: 8 Basic I/O Concepts

9. Logical Output-The L Descriptor The descriptor used to display logical data has the form rLw The value of a logical variable can only be.TRUE. or.FALSE. The output of a logical variable is either a T or an F, right justified in the output field. © 2010, Dr. ALİ CAN TAKİNACI Slide No: 9 Basic I/O Concepts

10. Character Output-The A Descriptor Character data is displayed by using the A format descriptor. rA or rA.w © 2010, Dr. ALİ CAN TAKİNACI Slide No: 10 Basic I/O Concepts

11. Horizontal Positioning-The X and T Descriptors The X descriptor has the form nX where n is the number of blanks to insert. It is used to add one or more blanks between two values on the output line. The T descriptor has the form Tc where c is the column number to go to. It is used to jump directly to a specific column in the output buffer. The T descriptor works much like a "tab" character on a typewriter, except that it is possible to jump to any position in the output line, even if we are already past that position in the FORMAT statement © 2010, Dr. ALİ CAN TAKİNACI Slide No: 11 Basic I/O Concepts

12. The course name begins in column 51 of the buffer, but it is printed in column 50, since the first character in the output buffer is the control character.) © 2010, Dr. ALİ CAN TAKİNACI Slide No: 12 Basic I/O Concepts

13. Repeating Groups of Format Descriptors We have seen that many individual format descriptors can be repeated by preceding them with a repeat count. For example, the format descriptor 2I10 is the same as the pair of descriptors I10, I10. © 2010, Dr. ALİ CAN TAKİNACI Slide No: 13 Basic I/O Concepts

14. Changing Output Lines-The Slash (/) Descriptor The slash (/) descriptor causes the current output buffer (line) to be sent to the printer, and a new output buffer to be started. © 2010, Dr. ALİ CAN TAKİNACI Slide No: 14 Basic I/O Concepts