ITEC 320: Program 4
Due: 11:59:59 Monday 4/17/17
Due: 11:59:59 Thursday 4/13/17
Submit command:
submit itec32001 calc.adb calcpkg.ads calcpkg.adb stackpkg.adb wordpkg.ads wordpkg.adb
Last modified:
Updates:
 2017 Apr 15 12:03:12 PM: Added information, in Other Points, on making sure that you create your data file on the same
OS as you are running.
 2017 Apr 10 08:18:52 AM: Struck out the phrase "command line" from the assignment description. Write your program to work correctly when standard input is redirected from a
file. You do not have to handle the complexities of standard input from the keyboard.
 2017 Apr 04 06:02:17 PM: Changed due date.
 2017 Apr 04 03:29:15 PM: Assignment checker now running.
Now available: You can see an example of this program at assignment checker (which uses gnoga to
integrate the GUI, web server, and problem solution). Oncampus or VPN session required.
Write a command line calculator that does 5 basic operations (+, , *, /, **).
Specifically, do the following:
 calc.adb: Write a simple client that reads calculations and prints each calculation and its result, as
shown in the example below.
 calcpkg.ads/adb: This packages provides commands to work with calculations.
You are to finish the specification and write the body.
 stackpkg.adb: Complete the implementation of this generic package,
using the specification and partial body given below.
You do not have to submit stackpkg.ads since you will not change it.
 wordpkg.ads/adb: Modify this package to add a to_string function.
You may add routines to any of the package specifications that you submit,
but do not modify the signatures of, or remove, any public routines from these packages.
You may submit additional packages if you want (eg stackpkg.utils).
Calculator Operation:
The operations operate on and return integers, except for ** which requires a Natural exponent.
Division is integer division.
Calculations are left associative, are done in normal precedence order
(ie ** is highest, * and / are middle, and + and  are low precedence),
and can contain parentheses.
The end of a calculation is marked by an =.
Calcpkg:
Your program is to implement the package calcpkg
which allows clients to work with calculations and which
has the following (incomplete) specification:
package calcpkg is
type Calculation is limited private;
procedure get(c: out Calculation);
procedure put(c: Calculation);
function to_string(c: Calculation) return String;
function length(c: Calculation) return Natural;
function Result(c: Calculation) return Integer;
private
...
end calcpkg;
You may add routines to the package specification, but do not change the
signatures of the given routines.
You must, of course, complete the private section.
The routines operate as follows:

Procedures get and put read a calculation from standard input and write one to standard
output, respectively.
If get is called when no calculations remain, it should return a calculation whose length is 0.
 Function length returns the number of operands and operators (including parentheses and equals) in a calculation.

Function to_string returns the calculation as a String,
with spaces between operators (including parentheses and =), as shown in the example below.

Function result returns the result of the Calculation.
Input:
In the input
all pairs of operators and operands, including = and parentheses, will be separated by white space (so
that wordpkg can be used for input).
No calculation will contain a total of more than 50 operands and operators (including parentheses and the =).
Client and Sample Run:
Your client (ie calc.adb) will be similar to the following:
c : Calculation;
begin
loop
get(c);
exit when length(c) = 0;
put_line(to_string(c) & result(c)'img);
end loop;
This input, when read from standard input:
11 + 2 =
2 +
3 * ( 4 + 5 )
=
2 ** 3 =
will produce the following on standard output:
11 + 2 = 9
2 + 3 * ( 4 + 5 ) = 29
2 ** 3 = 8
The lengths of the calculations above are 4, 10, and 4, respectively.
Wordpkg:
Modify wordpkg specification and body so that wordpkg provides this function:
function to_string (w : Word) return String;
with the obvious meaning.
Stack Package:
To create your stacks, you are to use the generic stack package whose
specification is given here
(which you may not modify).
To do this, you will need to write the
implementation (stackpkg.adb) for this
generic stack specification.
Other Points:
 You must use an enumeration type.
You may want to also create and use subtypes of your enumeration type.
 You may use unbounded strings in this assignment.
 If an error occurs (eg invalid input or overflow) then
your client should terminate gracefully (ie not crash).
 You may need to compile with gnato to turn on overflow checking
(eg gnatmake gnato calc.adb).
 It is an error for an exponent to be negative.
 Remember to test your program on rucs
 Also remember to create any data file using the same
system that you use to compile and run your program because
different operating systems use different line end characters.
On rucs you can use vim or pico to create a file.
You should actually type in the lines of the file,
since cutting and pasting from another source can
give the wrong kind of line end characters.
Follow these instructions use vim to change the line end characters:
 vim mydatafile.txt
 :set fileformat=unix
 :wq
Operator Precedence Evaluation:
To do the calculation you are to do operator precedence evaluation.
This requires two stacks that hold pending operations:
one for operands and one for operators (ie for
arithmetic operators and left parentheses).
The evaluation follows these rules:
 Operands and operators are examined in the order in which they
appear in the input.
 After an operand is examined, it is immediately put onto the operand stack.
 After a left parenthesis is examined, it is put on the operator stack.
 When an arithmetic operator is examined, it will eventually
be put on the operator stack,
but some other action might be required first, as
described next:
 An arithmetic
operator (call it X) CANNOT be put on the stack if the operator
currently on top of the stack (call it Y) is
of equal or higher precedence than X. If there
is an operator of equal or higher precedence on top of the stack,
then you must repeatedly evaluate each operator on top of the stack
until either the stack is empty or the top of the
operator stack has an operator of lower precedence than X.
At that point, the operator X is put on the stack.
 To evaluate an arithmetic operator that is on the stack,
pop the operator and its operands,
perform the operation, and push the result.
 As mentioned above, operator precedence is as follows:
"+" and "" are equal to each other and higher than "(" on the stack,
"*" and "/ are equal to each other and higher than "+",
and "**" is higher than "*".
The precedence of the operator "(" effectively changes when that operator
is moved from the input to the stack.
 When the operator being examined is a ")",
then the operators on the stack should be
evaluated until a "(" is found on the stack at which point the "("
is removed from the stack and the ")" is discarded.
At this point, of course, the value on top of the operand stack is the
value of the expression that was inside the parentheses.
 When an "=" is examined, the operations on the operator stack are
evaluated until that stack is empty.
For this example input "2 + 3 * (4 + 5 * 6) + 7 =",
the sequence of evaluation is this:
push 2, push +, push 3, push *, push (,
push 4, push +, push 5, push *, push 6
pop 6, pop 5, pop *, perform *, push 30,
pop 30, pop 4, pop +, perform +, push 34, pop (
pop 34, pop 3, pop *, perform *, push 102,
pop 102, pop 2, pop +, perform +, push 104,
push +, push 7,
pop 7, pop 104, pop +, perform +, push 111
At the end of the sequence given above, the operand stack contains only
111 and the operator stack is empty.
For brevity this example does no specify
which stack is being used, and
it does not show the calls to top needed before the calls to pop.
Submit:
Use the submit command to turn
your program in for grading, following
the submit command given at the beginning of the assignment.
You may submit as many times as you like,
but only the last submission is kept.