Here is a sample session from testing project4.

8 files were used for testing and they can be found here .

The first 5 files and the last file are error-free. Files 6 and 7 contain all the errors. Make sure you understand why each error occurs. Sufficient explanation is interspersed between the error messages. You may want to open a new browser window for viewing the data files along with this document.

Enter a file name: t1.txt
x = 3
y = 5
sum = 35

Type another file name or 'quit' to terminate the program: t2.txt
a = 1
b = 2

Type another file name or 'quit' to terminate the program: t3.txt
a = 1
b = 2
sum = 3

Type another file name or 'quit' to terminate the program: t4.txt
a = 1
b = 2
sum = 3
sum = 30
a = 10
b = 20
sum = 30

Type another file name or 'quit' to terminate the program: t5.txt
a = 0
b = 205239756490
sum = 7

Type another file name or 'quit' to terminate the program: t6.txt

Error: Undefined variable





Here, we are trying to use the variable a in RHS of line 1
without initializing it . Hence the error. 





Error: Undefined variable




Here, even though the variable a appears in LHS in line 1,
since line 1 contained an error , the assignment could
not succeed.Hence the variable a is undefined even
in line 2.






Type another file name or 'quit' to terminate the program: t7.txt

Error: Expecting a variable, found something else instead




This is because of missing the variable name in line 1.




Error: Expecting an assignment operator, found something else instead 




This is because of missing the = in line 2.




Error: Strange character




This is because of missing the expression in line 3.




Error: Expecting an assignment operator, found something else instead 




This is because of missing the = in line 4.
It is important to note that the statment since
the = operator is missing in line 4 , the characters
in the input are skipped until the next semicolon,
which is present in line 5.
Here, it actually doesn't perform a= 1+1 even though
that statment, as such , is  error-free.




Error: Not a valid operator




This is because of missing the operator in line 6.




Error: Strange character




This is because of using the - symbol in line 7.




Error: Strange character




This is because of missing the operand in line 8.




Error: Undefined variable




This is because of the variable  e 
being undefined in line 9.Again, though it is
appears in the LHS of line 8, since that assignment
statement was erroneous, the variable  e 
is not initialized.




Type another file name or 'quit' to terminate the program: t8.txt
thiscourse = 16
nextcourse = 17
dataStructures = 17
algorithms = 21
program = 38
Java = 13
nextSemThisCourse = 13
Compilation = 40
Execution = 60
total = 100
a = 100
something = 10
something = 15
forall = 1
aplus = 115
grade = 115


Type another file name or 'quit' to terminate the program: quit