Explain unstructured loops in detail?

Loops are one of the most important of the languages like C and C++. They have greatly reduced the drudgery of the programmers and developers which would otherwise have made the programming of a software system or application more hectic. The necessity of the loops cannot be ignored when it comes to the repetition of a particular executable statement or a block of statements in a program. 

In other words,

Say we have the below written statement in C++ programming language that we need to print only one time:

“hello! Welcome to C++ programming”

To print it one time we shall write the code like this:

Cout<<”hello! Welcome to C++ programming\n”;

Say now you need to print this statement a 100 times! What you are going to do- write the above C++ statement a 100 times? No! Certainly not! This is unfeasible and a complete waste of time! So what is the alternative that we have? Yes of course we have the “loops”. 

Using loop we will have to write only a small code instead of writing that C++ statement again and again for 100 times. Using loop we shall write like this:

For( int i = 1; i <=100; i++ )

{

Cout<<”hello! Welcome to C++ programming\n”;

}

The above loop is a for loop and it will the statement that we wish to be printed 100 times. See to how much extent our task has been reduced! This would not have been possible without loops. 

Loops generally are classified based on their types namely in to:

1. The while loop
2. The for loop
3. The do – while loop

But based up on their structure, they are classified in to two types:

1. Structured loops and
2. Unstructured loops

This article is all about the unstructured loops. We shall discuss them in detail. 

The Unstructured Loops

- The unstructured loops can be defined as the loops that are void of a single header or a node in the control flow graph that has all the nodes dominating the whole loop body. 

- The main problem that arises with these unstructured loops is of managing them.

- Managing them is such a hectic task.

- For analyzing the unstructured loops the programmers, developers and researchers have come up with so many ways but none of them seems to be so efficient.

- One of the ways is to use a control flow graph along with the scope graph corresponding to the function containing the unstructured loop to be analyzed. 

- This method involves attaching of each and every iteration counter with each of the loop header.

- Attaching the iteration counters in such a way can cause over estimation of the control flow. 

- So to overcome this problem, the iteration counters are attached to each basic block and this helps a great deal in achieving a lot of flow information. Even this way results in some disadvantage! 

- Therefore another method of managing the unstructured loops has been developed. 

- Another method has been developed for transforming the unstructured loops in structured ones. 

- If one looks at the unstructured loop with a view of the control flow graph they seem to have entry edges to one or more than one node all over the loop. 

- In another way we can say that an unstructured consists of parts of several different loops. 

- Several structured loops can also be merged in to an unstructured loop with the help of a code size optimizing compiler.

- A straight way has been developed for the elimination of the unstructured loops which is creating a scope with a single header for each entry of the loop. 

Loop testing is a white box testing technique - Explain?

Loop testing is also one of the white box testing techniques and thus requires a very deep knowledge about the software system or application. Loop testing methodology has been designed exclusively for the checking of the validation of the iterative constructs which are nothing but the loops.

Types of Loop Constructs
These loop constructs are 4 types as mentioned below:
1. Unstructured loops
2. Simple loops
3. Nested loops and
4. Concatenated loops

Tests applied to different Loop Constructs
Now we shall define some of the tests that can be applied to the above mentioned types of loop constructs under the context of the loop testing:

1. For unstructured loops only one thing is possible which is that they should be redesigned in order to form a structured construct and then can be tested accordingly.

2. For simple loops a number of allowable passes through them is specified first and then the following tests are applied:

(a) Skipping of the entire loop.
(b) Making only one pass through the loop.
(c) Making two passes through the loop.
(d) Making “p” passes through the loop where p is the maximum number of passes.
(e) Making “n-1”, “n”, “n+1” passes through the loop.

3. For nested loops simply the testing approach of the simple loops is extended but, the number of the test cases increases geometrically as per the number of the nested loops and the level of nesting. Usually the following steps are followed:

(a) The inner most loop is the starting point for the testing.
(b) All other loops are set to minimum possible values.
(c) Simple loop tests are conducted for the inner most loop and the outer loops or the nesting loops are kept in their minimum values only till the testing of the inner most loop is complete.
(d) For the excluded values more tests are added.
(e) Now once the testing of the inner most loop is complete, this loop including all the other nested loops are set to typical values and the testing moves outwards. The other nesting loops are held with their minimum values.
(f) The testing in this manner continues until and unless all the loops have been tested.

4. For concatenated loops also the approach that has been defined for the testing of the simple loops can be used but only if the either loops are independent of each other i.e., if the loop counter for one of concatenated loop is 1 and it is used as the executing value for the other loop, then the two loops are said to be dependent on each other and hence the simple loop approach cannot be followed for them.

More about Loop Testing

- It has been observed so many times that most of the semantic bugs preside over the loops.

- It becomes difficult for the path testing also to commence since there are so many paths generated via a loop and an infected loop leads to infected paths which makes even further difficult to track the bug.

- Some of testers believe that it is just enough to test the loop only two times but this is not a good practice.

- A loop should be tested at the following three instances:
a) At the entry of the loop
b) During the execution of the loop and
c) At the exit of the loop

- Loop testing is aimed at testing a resource multiple numbers of times by executing it under a loop and this whole process is controlled by a diagnostic controller.

- However, one rule has been defined for the loop testing which is that the user can interact only at the entry and exit of the loop and nowhere in between.

Loop testing - a white box testing technique and types of loop testing.

Loop testing is a kind of white box testing technique that focuses exclusively on the validity of loop constructs. Four classes of loops can be defined: Simple loops, Concatenated loops, Nested loops, and unstructured loops.

- Simple Loops: The following sets of tests can be applied to simple loops, where 'n' is the maximum number of allowable passes through the loop.
a) Skip the loop entirely.
b) Only one pass through the loop.
c) Two passes through the loop.
d) 'm' passes through the loop where m < n.
e) n-1,n,n+1 passes through the loop.

- Nested Loops: If we extend the test approach from simple loops to nested loops, the number of possible tests would grow geometrically as the level of nesting increases.
a) Start at the innermost loop. Set all other loops to minimum values.
b) Conduct simple loop tests for the innermost loop while holding the outer loops at their minimum iteration parameter values. Add other tests for out-of-range or exclude values.
c) Work outward, conducting tests for the next loop, but keep all other outer loops at minimum values and other nested loops to typical values.
d) Continue until all loops have been tested.

- Concatenated Loops: These loops can be tested using the approach defined for simple loops,If each of these loops is independent of the other. However, if two loops are concatenated and the loop counter for loop one is used as the initial value for loop two, then the loops are not independent.

- Unstructured Loops: Whenever possible, this class of loops should be redesigned to reflect the use of the structured programming constructs.