Programming Basics: Compilation and Interpretation

Study Notes

Program development is the process of creating new programs, and the Program Development Life Cycle (PDLC) is the process associated with creating successful applications programs.
PDLC consists of five phases: program analysis, program design, program coding, debugging and testing, and program maintenance.

Problem analysis is the first phase of PDLC, where a systems analyst and programmer review specifications and talk with users to fully understand what the software should do.
The outcome of problem analysis is documentation, which includes:
- Program specifications
- Timetable
- Language to be used
- Testing plan
- Required documentation

Program design is the second phase of PDLC, where planning tools are used to create a detailed design of the program.
Program design tools include:
- Flowcharts
- Pseudocode

Flowcharts use geometric symbols and relational operators to provide a graphic display of the sequence of steps involved in a program.
Flowcharts follow the same logical sequence as the program statements.
Different symbols are used to represent different actions, such as start/stop, decision, input/output, processing, and looping symbols.

Sequence control structure is a series of procedures that follow one another.
Controlling a repetition structure requires modifying the flowchart to change the value of the loop variable.
Examples of program design include:
- Average of 10 numbers using iteration with a while loop
- Calculating the area of a circle using pseudocode

Pseudocode uses English-like statements in place of graphic symbols.
Pseudocode is easy to modify and can be embedded into a program as comments.
Examples of pseudocode include:
- Calculating the average grade for a class of 100 students
- Displaying "pass" or "fail" based on a student's grade

Coding is the third phase of PDLC, where the program is written in a programming language.
The programming language must be chosen, and coding standards should be adhered to.
Reusable code and data dictionaries should be used to translate the coded program into executable code.

Debugging is the process of making sure a program is free of errors or bugs.
Preliminary debugging finds syntax or logic errors, and testing can consist of alpha or beta testing.
Types of errors include:
- Syntax errors: occur when the programmer has not followed the syntax rules of the language.
- Logic errors: result when the command syntax is correct but the program is producing incorrect results.
- Runtime errors: occur when the program is running, such as dividing by zero or accessing a non-existent file.

Program maintenance is the process of updating software to ensure it continues to be useful.
Maintenance is a costly process, but it can be used to extend the life of a program.
Documentation consists of amended program packages reflecting what problems occurred and what program changes were made.

Machine and assembly languages are called low-level languages, because they require programmers to write instructions at the finest level of detail.
High-level languages require less coding detail and make programs easier to write, but need to be translated into machine language before they can be executed.
Examples of high-level languages include:
- BASIC
- COBOL
- Pascal
- C
- Java
- Python