1. Lecture 3 : January 2001 Dr. Andrew Paul Myers
FORTRAN 77 Programming.
Lecture 3 : January 2001
Dr. Andrew Paul Myers
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2. Array Variables.
An array is a simple structure, capable of storing many variables of the same type in a single data structure.
Declare arrays with other variables.
Arrays can be of any data type.
Declaration :
REAL array(100)
INTEGER loop(20),data(500)
CHARACTER names(10)*20
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3. More on Arrays.
Each array member is addressable by an array subscript.
e.g for REAL x(10), subscripts range from 1 to 10. i.e. array(1), … array(10)
The subscript may be a constant, variable or expression :
array(1)=SIN(x)
array(loop)=4.0*array(loop-1)
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4. And There’s More… Consider : REAL array(10)
As mentioned before, array subscripts range from 1 to 10.
We can over ride this default:
REAL array(-10:10)
INTEGER data(0:200)
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5. Still more… Arrays can be multi-dimensional REAL array(5,2)
i.e. array(1,1), array(1,2), array(2,1)…
Taking things to an extreme!!!
REAL array(5,0:12,20,-10:100)
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6. Iterations. Loops allow blocks of command to be repeated.
Simplest is the DO loop.
DO <index> = <start>,<stop> [,<step>]
<statement(s)>
END DO
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7. Example DO Loop. INTEGER loop REAL array(100) DO loop=1,100,1
array(loop)=0.0
END DO
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8. DO WHILE Loop. Another type of loop : DO WHILE <condition>
<statement(s)>
END DO
Not in all versions of FORTRAN 77.
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9. Example. INTEGER test test=15 DO WHILE ( test .GT. 12 ) test=test-1
END DO
Useful for repeating a program?
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10. The Horrible Past… DO loop with numeric label. DO 1000 loop=0,10,2
<statement(s)>
1000 CONTINUE
Implied DO loop!
READ*,(value(loop),loop=1,10,1)
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11. The DATA statement.
Another method of assigning values to variables and arrays.
REAL a,b,c
INTEGER d(5),lots(100)
CHARACTER single(5)*1
DATA a /1.5/
DATA b,c /2.5,5.6/
DATA d /1,2,3,4,5/
DATA lots /100*0.0/
DATA single /5*’Y’/
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12. Advanced Data Types. Structures. Not in all versions of F77.
Structures can hold many variables of different types.
Structures are declared with all other variables at the beginning of a program.
With structures you can build powerful, custom data types.
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13. Declaring A Structure. STRUCTURE / book_type / CHARACTER title*80
CHARACTER author*40
INTEGER stock_level
REAL price
END STRUCTURE
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14. The Next Step…
Now we must declare a record of the type defined in the structure.
RECORD / book_type / science
RECORD / book_type / rubbish(10)
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15. Value Assignments. Each part of the record is identified thus :
science.title = ‘2001’
science.author = ‘A.C.Clarke’
science.stock = 25
science.price = 9.99
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16. For the More Brave… Remember? RECORD / book_type / rubbish(10)
DO loop=1,10
READ’(A80)’,rubbish.title(loop)
READ*,rubbish.price(loop)
END DO
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