Additional Notes

!!!REMEMBER!!!

• Make sure you have all 8 required items in the header of your programs
• Use the modification section of the program to describe compile errors you encountered and how you solved them. This may prove useful to you in the future

Note that

• FORTRAN is unusual in that it stores the values of multi-dimensional arrays in column-major order while most languages store the values in row-major order.
• In order to retrieve elements stored in an array, the address of a particular element must be computed. the computation is different for arrays stored in row-major and column-major order.
• We will learn how these computations are done later in the semester. For now, the basic idea computation is:

Base Address + Width of Element * number of elements to skip

• In Java, all parameters are passed by value. The value is either a literal (in the case of primitive parameters) or an address (in the case of object parameters). In either case, a copy of the parameter is passed to the method that uses it.
• In FORTRAN, all parameters are passed by reference (i.e. address). This means that changes made to formal parameters in sub-programs are immediately reflected in the actual parameters.

The following remarks were made when we looked at and discussed SUBROUTINE SILLY

· NUM1 and NUM2 are integers because they start with an N

· WRITE(6,12) : 6 was associated with a specific output device, and 5 was associated with a specific input device. This made the programs portable.

· WRITE(6,12) : 12 is a label referring to a FORMAT statement (format descriptor)

· FORMAT(1X, I10, I10) is a FORMAT statement.

o I10 means is an integer right justified in a field of 10

o In a READ statement I10 would pick up 10 columns worth of digits as an integer

o In a READ statement F10.5 would pick up 10 columns worth of digits and place the decimal point to the left of the last 5 of them (i.e. 10 is the total number of columns picked up, 5 is the number of digits after the decimal point) Note that IF there were a decimal point within the 10 columns, it would override the format.

!!!REMEMBER!!!

• You need a ‘FORMAT’ for every ‘write’ and every ‘read’
• The following example shows how you can output a string without an associated value

WRITE (6, 10)

10 FORMAT (1X, “This is a royal pain”)

• Meaning of “1X “ in output statements
• old line printer devices which had a roller or platen known as the carriage
• the first element in each OUTPUT statement was a carriage control character
• Carriage control characters(no effect today):
• 1X or ‘ ‘ = new line
• 0 = double space
• 1 = go to a new page
• + = suppress line spacing

In the old days, we were able to do this:

• CALL SILLY (2, 3) because there was a function: everything was passed by reference

computed GO TO = multiway branch

Example2.f = syntax illustration of a computed GO TO statement

I = 5

GO TO (15, 26, 43, 56, 12) I

If I is greater than 5 it will go to the next line of code instead of transferring to one of the numbered statements

Various subsequent versions of the program are on the web.

• Example2 – was a bad program because the value of I was hard coded
• Example2v2 – only reads a single value (it does not check all the values)
• Example 2v3 – has inaccurate directions (it says integers 1-10 but actually works for all integers)
• Example 2v4 – is better but doesn’t handle erroneous input (i.e. characters or real numbers

!!!REMEMBER!!!

• 2 pts off for inaccurate directions to user
• 1 point off if we leave out the “STOP”

DIMENSION statements were used in early Fortran for arrays and identifiers for arrays used names representing the default types.

Input and output files:

C:\ prog1 < one.txt (input)

C:\ prog1 > one.txt (output)

C:\prog1 < one.in > one.out

C:\prog1 <adams.in > chip.out

These statements refer to the FORTRAN NOTES:

· (7) values in DATA statements are assigned to variables at compile time. DATA statement are not executable statements

· (10) Answer = SUM(5.0, 6.0, 7.0) – SUM (5.0, 6.0, 7.0) is a call to FUNCTION SUM. The returned value replaces the call and needs to be assigned (stored) in another variable. No recursive function calls in early FORTRAN. Partially due to the convention of storing the return address in a particular register.

· (11) ERR= label – was an early exception handling statement. Used when inputting data. If the wrong type of data was entered control would transfer to the statement with the label label.