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Welcome to the Fibonacci in Algol68 page! Here, you'll find the source code for this program as well as a description of how the program works.

```
MODE PARSEINT_RESULT = STRUCT(BOOL valid, INT value, STRING leftover);
MODE PARSEINTLIST_RESULT = STRUCT(BOOL valid, REF []INT values);
PROC parse int = (REF STRING s) PARSEINT_RESULT:
(
BOOL valid := FALSE;
REAL r := 0.0;
INT n := 0;
STRING leftover;
# Associate string with a file #
FILE f;
associate(f, s);
# On end of input, exit if valid number not seen. Otherwise ignore it #
on logical file end(f, (REF FILE dummy) BOOL:
(
IF NOT valid THEN done FI;
TRUE
)
);
# Exit if value error #
on value error(f, (REF FILE dummy) BOOL: done);
# Convert string to real number #
get(f, r);
# If real number is in range of an integer, convert to integer. Indicate integer is valid if same as real #
IF ABS r <= max int
THEN
n := ENTIER(r);
valid := (n = r)
FI;
# Get leftover string #
get(f, leftover);
done:
close(f);
PARSEINT_RESULT(valid, n, leftover)
);
PROC usage = VOID: printf(($gl$, "Usage: please input the count of fibonacci numbers to output"));
COMMENT
fib(n) = fib(n - 1) + fib(n - 2)
where:
- fib(0) = 0
- fib(1) = 1
COMMENT
MODE FIBSTATE = STRUCT(INT prev, INT result);
PROC init fib = FIBSTATE: FIBSTATE(0, 1);
OP FIB = (FIBSTATE state) FIBSTATE: (result OF state, prev OF state + result OF state);
OP FIBRESULT = (FIBSTATE state) INT: prev OF state;
PROC show fibonacci values = (INT n) VOID:
(
# Initialize Fibonacci state #
FIBSTATE state := init fib;
# Update Fibonacci state and show results for requested number of values #
FOR k TO n
DO
state := FIB state;
printf(($g": "gl$, whole(k, 0), whole(FIBRESULT state, 0)))
OD
);
# Parse 1st command-line argument #
STRING s := argv(4);
PARSEINT_RESULT result := parse int(s);
# If invalid or extra characters, exit #
INT n := value OF result;
IF NOT (valid OF result) OR (leftover OF result) /= ""
THEN
usage;
stop
FI;
# Show requested number of Fibonacci values #
show fibonacci values(n)
```

Fibonacci in Algol68 was written by:

- rzuckerm

If you see anything you'd like to change or update, please consider contributing.

No 'How to Implement the Solution' section available. Please consider contributing.

No 'How to Run the Solution' section available. Please consider contributing.