Is there any similarity between if else if and nested if?

  nested if

    **if(condition)**
    {
       **if(condition)**
       {
          statement-1;
       }
       else
       {
         statement-2;
       }
    }
    else
    {
        if(condition)
        statement-3; 
        else
        statement-4;
    }
      

if else if 

  if(condition)
  statement-1;
  **else if**(condition)
  statement-2;
  else
  statement-3;

ANSWER:Look above syntax of both bidirectional. The nested if is an if statement used within another if statement.When we use if else if then an if statement is used within the else part of another if in this way,'nested if is similar to an if else if statement.

i did not understand above answer.

"If" I'm understanding you correctly (pun not really intended)...

You can often think of else if as taking advantage of the fact that, in the absence of curly braces, an if or else "block" will be the next statement. And if that next statement is an if then the whole structure of that if is considered to be that statement.

What that means is this:

if (someCondition) {
  //...
} else if (anotherCondition) {
  //...
}

Is the same as this:

if (someCondition) {
  //...
} else {
  if (anotherCondition) {
    //...
  }
}

It becomes a little more clear if you remove more of the curly braces, and move the second if to its own line. This is also the same as the above:

if (someCondition)
  //... one statement
else
  if (anotherCondition) {
    //... more statements
  }

Structurally these are all the same. And the compiler may even produce the same resulting output. (Though I wouldn't be surprised if it added more tweaks for efficiency and such. Compilers are good at that sort of thing.)

So basically an else if is just an else with no curly braces, where the only statement within that else block is another if structure.

They don't cover the same use cases. For exemple in the nested if there is -1 when both conditions a and b are true, but in the else if it only requires the condition a.

Here is the differences

    if (a) {
      if (b) {
        //  a && b
      } else {
        //  a && !b
      }
    } else { 
      //  !a
    }

    if (a) {
      // a
    } else if (b) {
      // !a && b
    } else {
      // !a && !b
    } 

The they are similar. But they are not the same.

One way to understand the differences is to write out the "truth tables" for the two versions. Note that we need to distinguish the two conditions to understand the nature of the differences.

# version 1
if (condition-a) {
    if (condition-b)
        statement-1;
    else
        statement-2;
} else 
    statement-3;

condition-a   condition-b  =>
   false         false     => statement-3   | NOT A
   false         true      => statement-3   |
   true          false     => statement-2   | A AND NOT B
   true          true      => statement-1   | A AND B

Now the alternative version

# version 2
if (condition-a)
    statement-1;
else if (condition-b)
    statement-2;
else
    statement-3;

condition-a   condition-b  =>
   false         false     => statement-3   | NOT A AND NOT B
   false         true      => statement-2   | NOT A AND B
   true          false     => statement-1   | A
   true          true      => statement-1   |

As you can see, the truth tables are different. I have also added the equivalent "boolean logic"

OK, so how did I work out the truth tables? Answer: by "hand executing" the code. You can do the same thing to check that I have gotten the tables correct AND to understand the logic behind the differences.

If you are trying to understand the answer that you have posted, yes, the last if condition in a "if else if" condition can be called as a "nested if condition".

else and if are two separate keywords, so you can split and indent for better readability.

  if(condition)
    statement-1;
  else 
    if(condition)
      statement-2;
    else
      statement-3;