Computer program structure

Programming glossary

The following table contains some technical programming phrases that are often used and heard in the field of computer science and programming, that you need to be familiar as well.

The contents of a computer program

Although different programming languages look different in their syntax standards, virtually all programming languages are comprised of the following major compnents (instructions):

1. input
   Virtually every program starts with some input data by the user, or the input data that is hard-coded in the program.
   
   
2. mathematical/logical operations
   Virtually all programs involve some sort of mathematical or logical operations on the input data to the program.
   
   
3. conditional execution
   In order to perform the above operations on data, most often (but not always) there is a need to check if some conditions are met in the program, and then perform specific programming instructions corresponding to each of the conditions.
   
   
4. repetition / looping
   Frequently it is needed to perform a specific set of operations repeatedly in the program to achieve the program’s goal.
   
   
5. output
   At the end of the program, it is always needed to output the program result, either to a computer screen or to a file.

Debugging a program

As it is obvious from its name, a bug in a computer program is annoying programming error that needs fixing in order for the program to become executable or to give out the correct answer. The process of removing program bugs is called debugging. There are basically three types of programming bugs (errors):

Syntax error

A program, whether interpreted or compiled, can be successfully run only if it is syntactically correct. Syntax errors are related to the structure and standard of the language, and the order by which the language tokens are allowed to appear in the code. For example, the following Python print statement is a syntax error in Python 3 standard, whereas it was considered to be the correct syntax for print in Python 2 standard.

print 'Hello World!'

  File "<ipython-input-21-10fdc521e430>", line 1
    print 'Hello World!'
                       ^
SyntaxError: Missing parentheses in call to 'print'

The syntactically-correct usage of print in Python 3 would be,

print ('Hello World!')  

Hello World!

Runtime error

Runtime errors or sometimes also named exceptions are a class of programming errors that can be detected only at the time of running the code, that is, they are not syntax errors. Examples include:

• memory leaks (very common error in beginner C and C++ codes)
• uninitialized memory
• access request to an illegal memory address of the computer
• security attack vulnerabilities
• buffer overflow

These errors can be sometimes tricky to identify.

Semantic error

Unlike syntax errors that comprise of something the compiler/interpreter does not understand, semantic errors do not cause any compiler/interpreter error messages. However, the resulting compiled/interpreted code will NOT do what it is intended to do. Semantic errors are the most dangerous types of programming errors, as they do not raise any error flag by the compiler/interpreter, yet the program will not do what it is intended to do, although the code may look perfectly fine on its face. A semantic error is almost synonymous with logical error. Dividing two integers using the regular division operator / in Python 2 and expecting the result to be real, would result in a semantic error. This is because, in Python 2 standard, the regular division operator is equivalent to integer division for integer operands:

In Python 2,

2/7

0

Whereas, you might have really meant a float division by using /, as in Python 3,

2/7

0.2857142857142857