Nested if statements:

You can also include, or nest, if statements within another if statement.
For example:

int mark = 100;

if (mark >= 50) {  
  cout << "You passed." << endl;
  if (mark == 100) {
    cout <<"Perfect!" << endl;
  }
}
else {  
  cout << "You failed." << endl;
}

Output:

You passed.  
Perfect!  

Nested if else Statements:

C++ provides the option of nesting an unlimited number of if/else statements.
For example:

int age=18;  
if(age>14)  
{
  if(age>=18)
 {
    cout<<"Adult";
 }
  else
 {
    cout<<"Teenager";
 }
}
else  
{
  if (age > 0)
 {
    cout<<"Child";
 }
  else
 {
    cout << "Something's wrong";
 }
}

Output:

Adult