Every loop has four elements that are used for different purposes. These elements are:
1. Initialization expression
2. Test expression
3. Update expression
4. The body of the loop
Initialization expression(s): The control variable(s) must be initialized before the control enters into the loop. The initialization of the control variable takes place under the initialization expressions. The initialization expression is executed only once in the beginning of the loop.
Test Expression: The test expression is an expression or condition whose value decides whether the loop-body will be executed or not. If the expression evaluates to true (i.e., 1), the body of the loop is executed, otherwise, the loop is terminated.
In an entry-controlled loop, the test expression is evaluated before entering into a loop whereas in an exit-controlled loop, the test expression is evaluated before exiting from the loop.
Update expression: It is used to change the value of the loop variable. This statement is executed at the end of the loop after the body of the loop is executed.
The body of the loop: A statement or set of statements forms a body of, the loop that is executed repetitively. In an entry-controlled loop, first, the test expression is evaluated and if it is nonzero, the body of the loop is executed otherwise the loop is terminated. In an exit controlled loop, the body of the loop is executed first then the test expression is evaluated. If the test expression is true the body of the loop is repeated otherwise loop is terminated.

(i) if nested inside if par

(ii) if nested inside else part

(iii) if nested inside both if part and else part

(i) For:
for (initialization(s); test-expression; update expression(s))
{
for (initialization( s); test-expression; update expression(s))
{
statement( s);
}
statement(s);
}
(ii) while: while( condition)
{
while( condition)
{
statement(s);
}
statement(s);
}
(iii) do while :
do
{
statement(s);
do
{
statement(s);
}while( condition);
} while( condition );

When a switch is a part of the statement sequence of another switch, then it is called as nested switch statement. The inner switch and the outer switch content may or may not be the same.
The syntax of the nested switch statement is:
switch (expression)
{
case constant 1:
statement( s);
break;
switch( expression)
{
case constant 1:
statement(s);
break;
case constant 2:
statement(s);
break;
.
.
.
default:
statement( s);
}
case constant 2:
statement(s);
break;
.
.
default:
statement(s);
}
Example:
switch (a)
{
case 0:
cout < "The Number is: zero" << endl;
break;
default:
cout < "The Number is a non-zero integer' < xendl;
intb = a % 2;
witch (b)
{
case 0:
cout << "The Number is even" << endl;
break;
case 1:
cout << "The number is odd' << endl;
break;
}
}

The switch statement is a multi-way branch statement. It provides an easy way to dispatch execution to different parts of code based on the value of the expression. The switch statement replaces multiple if-else sequence.
The syntax of the switch statement is:
switch( expression)
{
case constant 1:
statement( s);
break;
case constant 2:
statement( s);
break;
default:
statement(s);
}
Example:
#include < iostream.h >
using namespace std;
int main( )
{
int num;
cout << "\n Enter week day number:";
cin >> num;
switch (num)
{
easel : cout << "\n Sunday";break;
case2 : cout << "\n Monday";break;
case3 : cout << "\n Tuesday";break;
case4 : cout << "\n Wednesday";break;
case5 : cout << "\n Thursday'xbreak;
case6 : cout << "\n Friday";break;
case7 : cout << "\n Saturday";break;
default: cout << "\n Wrong input.. ...";
}
}
Output:
Enter week day number: 6
Friday