LOOPS IN FLOW GRAPHS:
Take source code as shown below.
a = 0;
b = b+c;
c = 0;
If (a>d)
{
c = b;
b++;
}
else
{
c = d;
d++;
}
a= b+d;
Basic blocks in above source code are
(1)

(2)

(3)

(4)

a = 0;
b = b+c;
c = 0;
If (a>d)

c = b;
b++;

c = d;
d++;

a= b+d;

Flow graph for above Basic blocks 