Transcript Programming Life Cycle (Compilers)

Lecture 2
Programming life cycle
computer piano analogy
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Piano + player - computer hardware
Musical score/notes - software or program
Composer - programmer
A music box is set with one melody – similar
to a microwave's preset computer chip
Algorithm
• An algorithm is a set of steps to accomplish a task
• High level language and source code are
synonyms. Examples include C, C++, Pascal, Java,
COBOL, Fortran, Python …
• All these languages have very specific syntax. This
allows a compiler program to read them and
translate them into machine code.
• Machine code-the final executable file that can
be run as an application.
HLL, pseudocode, syntax
• All High level Languages (HLL) have similar
constructs such as a "while" loop, "if then"
statements and others. Therefore a programmer
often first writes code in Pseudocode.
• Pseudocode- code that almost source code but
cannot be run through a compiler since it does
not have the correct syntax.
• Syntax- the exact proper way a HLL must be
written in for a compiler program to work.
Compiler
• source code
machine code
Compiler
• Source code is stored in a simple text file
• machine code is stored in an executable file or
an application file.
Sample pseudocode 2
Registration system in BC.
• First we will keep all information in two tables (on the
hard disk but copied to RAM when the program runs:
– The first is a students table that has students� addresses,
courses taken or registered for and grades. �
– The second is a course database that has the course
number, hours, number enrolled and enrollment limit.
• Enter all courses that will be offered this semester
• If a new student comes to register enter name into
student database
• For each course a student wants to take
– i. If the course is not full, in the course table increment the
number enrolled and in the student table enter the course
number for that student.
– ii. If the course is full inform the student that they would
need an overtally.
Sample pseudocode 1
average entered grades
• prepare the following three variables (a spot in
memory to store things):
– nstudents- number of grades entered so far, sum-sum
of grades so far, avg-average of grades
• while entered grade from user is still not negative
– nstudents = nstudents+1
– read another grade from user
– add grade to sum
• avg=sum/nstudents
• print avg to the screen