Tutorial6: DD Path Testing: Case of a Quadratic Equation
Objective of the Tutorial: To draw a Flow Graph, a DD Graph, calculation of Cyclomatic Complexity V(G) and find out all independent paths from the DD paths graph, for the case of quadratic equation ax^{2 } + bx + c = 0 where three coefficients a, b and c roots are calculated. The output may be real roots, imaginary roots or equal roots or even the equation may not be a quadratic equation.
When we have a flow graph, we can easily draw another graph that is known as decisiontodecision or (DD) path graph, wherein we lay our main focus on the decision nodes only. The nodes of the flow graph are combined into a single node it they are in sequence.
Process of constructing the DD Graph leading to computation of Cyclomatic Complexity goes like this:
Step 1: Start writing the following program

style="LETTERSPACING: 0.3pt"> # include
# include
# include
(1) int main ( )
(2) {
(3) int a, b, c, d, boolean = 0;
(4) double D;
(5) printf (nt Enter `a' coefficient :");
(6) scanf ("%d", & a) ;
(7) printf ("nt Enter `b' coefficient :);
(8) scanf ("%&d", & b);
(9) printf (nt Enter `c' coefficient :);
(10) scanf, ("%d, & c) ;
(11) if ((a > =0) && (a < = 00) && (b > = 0) && (b < =100) && (c > =0) && (c < =100)) {
(12) boolean = 1;
(13) if (a = = 0) {
(14) boolean = 1;
(15) }
(16) }
(17) if (boolean = = 1) {
(18) d = b * b 4 * a * c;
(19) if (d = = 0) {
(20) printf ("roots are equal and are r1= r2 = %f  b/(2 * float)&));
(21) }
(22) else if (d > 0) {
(23) D = sqrt (d);
(24) printf ("roots are real and are r1=%f and r2=%f; (b  D)/(2 * a), (b + D)/(2 * a));
(25) }
(26) else {
(27) D = sqrt (d) / (2 * a);
(28) printf ("roots are imaginary");
(29) }
(30) }
(31) else if (boolean = = 1) {
(32) printf ("Not a quadratic equation");
(33) }
(34) else {
(35) printf ("Invalid input range ...);
(36) }
(37) getch ( ):
(38) return 0;
(39) } Step 2: Draw the following Flow Graph
Step 3: Draw the following DD Path Graph
Since, nodes 110 are sequential nodes in the above flow graph, hence they are merged together as a single node a.
Since node 11 is a decision node, thus we cannot merge it any more.
Likewise we can go on deciding the merging of nodes & arrive at the following DD Path Graph
We get following decision table.
Nodes in Flow Graph 
Corresponding Nodes of DD Path Graph 
Justification 
1 9 
a 
Are Sequential Nodes 
10 
b 
Decision Nodes 
11 
c 
Decision Nodes 
12, 13 
d 
Sequential Nodes 
14 
e 
Two Edges Combined 
15, 16, 17 
f 
Sequential Nodes 
18 
g 
Decision Nodes 
19 
h 
Decision Nodes 
20, 21 
i 
Sequential Node 
22 
j 
Decision Node 
23, 24 
k 
Sequential Node 
25, 26, 27 
I 
Sequential Nodes 
28 
m 
Three Edges Combined 
29 
n 
Decision Node 
30, 31 
o 
Sequential Node 
32, 33, 34 
p 
Sequential Nodes 
35 
q 
Three edges Combined 
36, 37 
r 
Sequential Exit Nodes 
Step 4: Calculation of Cyclomatic Complexity V(G) by three methods
Method 1: V(G) = e n + 2 ( Where e are edges & n are nodes)
V(G) = 24 19+ 2 = 5 + 2 = 7
Method 2: V(G) = P + 1 (Where P No. of predicate nodes with out degree = 2)
V(G) = 6 + 1 = 7 (Nodes d, b, g, I, o & k are predicate nodes with 2 outgoing edges)
Method 3: V(G) = Number of enclosed regions + 1 = 6+1=7 ( Here R1, R2, R3, R4, R5 & R6 are the enclosed regions and 1 corresponds to one outer region)
V(G) = 7 and is same by all the three methods.
Step 5: Identification of the basisset with Seven Paths
Path 1: 
a b f g n p q r 
Path 2: 
a b f g n o q r 
Path 3: 
a b c e g n p q r 
Path 4: 
a b c d e g n o q r 
Path 5: 
a b f g h i m q r 
Path 6: 
a b f g h i k m q r 
Path 7: 
a b f g h j l m q r 
Conclusions from the above tutorial:
Conclusion 1: Each of these paths consists of at least one new edge. Hence this basis set of paths is NOT unique.
Conclusion 2: Test cases should be designed for the independent path execution as identified above.
Conclusion 3: We must execute these paths at least once in order to test the program thoroughly.
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