CHARACTER DATA

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Character data

We have extensively used REAL and INTEGER data types.

There is also:

CHARACTER data COMPLEX data LOGICAL data

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COMPLEX numbers take the form:

Z = X + iY

where X and Y are both real numbers

and i2 = -1, so that i = (-1)

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Z = X + iY

X is called the real part of Z {denoted Re(Z)}

REAL (X) value

Y is called the imaginary part of Z {denoted Im(Z)}

AIMAG (X) value

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Fortran stores Z as two real numbers: X and Y

When you write

PRINT*,Z

You get: (12.0, -9.0)

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CHARACTER DATA

Letters, spaces, punctuation marks

Combined into something called a STRING

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Written in code as follows:

“STRING” or ‘STRING’

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Declared as follows:

CHARACTER (n) :: string

Where “n” is the length = number of characters in the string

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example:

CHARACTER (3) :: month

Then “month” is type character with 3 elements, such as

jan feb mar

Perhaps you want to print a table of results with the month printed at the top … see later for format!

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Other ways to declare:

CHARACTER (LEN=n) :: string1

CHARACTER :: string2

Length in 2nd example is assumed to be ONE!!!

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Other ways to declare:

CHARACTER :: stringa*10, stringb*20, stringc*25

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To specify the value of a string:

CHARACTER (8) :: namename=“John Doe”

Note that the space counts as a character!!

CHARACTER (21) :: filenamefilename=“temperature_data_2005”

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Formatted read/write of a string:

In the FORMAT statement, use the descriptor:

“An”

As in: format (1x, I5, A20, F10.2)

Options: “I”, “F”, “E”, and now…”A” (also “D”…last slides)

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Unformatted read/write:

CHARACTER (3) :: MONTHINTEGER :: NUMBERREAD*,MONTH, NUMBER

You might enter: “JAN” 150

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Defects of character (hahaha!)

If a string is read in that is too long, it is truncated on the right.

CHARACTER (6) :: DAYDAY = “WEDNESDAY”

DAY is stored as WEDNES

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If a string is read in that is too short, it is padded with blanks on the right.

CHARACTER (12) :: DAYDAY = “WEDNESDAY”

DAY is stored as “WEDNESDAY ”

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Character data can be “added” !!!

The operation is called: concatenation “cat” for short

character :: first*5, second*6, third*11first = ‘minor’second = ‘ thing’third = first // second

produces… third = ‘minor thing’

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Useful??? Creation of file names inside some code…

character :: first*9, second*4, third*9character :: title*22first = ‘data-for-’third = ‘-smoothed’ DO YEAR = 1,10 if (year == 10) then second = ‘2010’ title = first // second // third endif! Produces title = ‘data-for-2010-smoothed’OPEN (15, file=‘title’) END DO

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DOUBLE PRECISION data…

Suppose you declare:REAL :: TEMP

and later print a value with PRINT*,TEMP

a number with certain number of digits after the decimal.

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Instead if you declare:DOUBLE PRECISION:: TEMP

and later print a value with PRINT*,TEMP

® a number with DOUBLE the number of digits after the decimal.

® Double precision!

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This may happen if you get some code that has run on a high-end machine (e.g., 64-bit)

and you now want to run it on a cheapo workstation (e.g., 16-bit)

… less resolution of numbers … less accuracy

See page 230 !!

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