Programming Fundamentals/Structured Programming

Overview

Structured programming is a programming paradigm aimed at improving the clarity, quality, and development time of a computer program by making extensive use of the structured control flow constructs of:

• Selection (if/then/else)
• Repetition (while and for)
• Block Structures
• Subroutines

This is in contrast to using simple tests and jumps such as the "go to" statement, which can lead to “spaghetti code”; code that is potentially difficult to follow and maintain.

Discussion

One of the most important concepts of programming is the ability to control a program so that different lines of code are executed. The mechanisms that allow us to control the flow of execution are called control structures. Flowcharting is a method of documenting (charting) the flow (or paths) that a program would execute. There are three main categories of control structures:

Sequence – Sequence is code that is the most familiar and easiest to read. The code is read in an a to z order. Think of reading a book. You read chapter to chapter in sequential order.

<script>
    var a = 1;
    var b = 2;
    var c = 3;
    a = b;
    c = a;
<script>

Selection – Select between two or more conditions. The choice is decided by asking a question. The answer determines the path to be executed.

<script>
    var a = 1;
    var b = 2;
    if (a         {
        var text = “I know a < b, it’s a bit obvious”;
        document.getElementById(“demo”).innerHTML =text;
        }
</script>

Iteration – Also known as repetition, it allows some code s) to be executed or repeated several times. The code might not be executed at all, executed a fixed number of times or executed indefinitely until some condition has been met. Iteration is also known as looping because the code shows the flow looping back to repeat the task. For example, a while loop is used to repeat back based on what condition is asked.

<script>
    var a = 0;
    var b = 10;
    result = “a < b”;
    text = “ “;
    while(a < b)
        {
        text += result + “<br>”;
        a++;
        }
    document.getElementById(“demo”).innerHTML = text;
</script>

Branching – An uncontrolled structure that allows the flow of execution to jump to a different part of the program. This category is rarely used in modular structured programming. For example, and if/else statement depending on the condition.

<script>
var x="";
var time=new Date().getHours();
if (time<20)
  {x="Have Good day";
  }
else
  {x="Have Good evening";
  }
document.write(x);
</script>

All high-level programming languages have control structures. All languages have the first three categories of control structures (sequence, selection, and iteration). Most have the if then else structure (which belongs to the selection category) and the while structure (which belongs to the iteration category). After these two basic structures, there are usually language variations.

The concept of structured programming started in the late 1960’s with an article by Edsger Dijkstra. He proposed a “go to less” method of planning programming logic that eliminated the need for the branching category of control structures. The topic was debated for about 20 years. But ultimately – “By the end of the 20th century nearly all computer scientists were convinced that it is useful to learn and apply the concepts of structured programming.”

Key Terms

branching

An uncontrolled structure that allows the flow of execution to jump to a different part of the program.

control structures

Mechanisms that allow us to control the flow of execution within a program.

iteration

A control structure that allows some lines of code to be executed many times.

selection

A control structure where the program chooses between two or more options.

sequence

A control structure where the program executes the items in the order listed.

spaghetti code

A phrase that is used to express disapproval for source code that is unstructured and difficult to maintain.

structured programming

A method of planning programs that avoids the branching category of control structures.

References

• cnx.org: Programming Fundamentals – A Modular Structured Approach using C++

Programming Fundamentals