An If statement is inside another if statement is termed as nested if statement. This type of control structures is called conditional branching.

   if(expression)
      { if (expression)
          {Statements}
        else
          {Statements} 
      }
   else
      { Statements }

  #include <iostream.h>
  using namespace std;
  int main(void)
    {
     int age;
     cout << "Enter your Age::";
     cin >> age;
     if (age >=10 && age<=50)
      { 
        if  (age >=10 && age <= 18)
            {cout  <<  "You are a Teenage"  << endl;}
         else 
            { cout << "You not a Teenager" << endl;}
       }
     else
        { cout  <<  "You are more than 50 years"  << endl;}
     return 0;
    }

   Enter your Age::51
   You are more than 50 years

In the above example, the conditional branching nested if statement is used to check two conditions in a nested loop. First "if" statement checks if the age is between 10 to 50 if true, another if loop checks if the age is between 10 to 18.