if/else and if/elseif

Question

If I have a statement block like this:

if (/*condition here*/){ }
else{ }

or like this:

if (/*condition here*/)
else if (/         


        

Answer 1

if you want to check more condition we can use if..elseif. single condition then we can use if or if...else.

Here I can't able to upload the full explanation with example so please go through the following links.

if..else statement details
http://allinworld99.blogspot.in/2016/02/ifelse-flow-chart-with-easy-example.html
if...elseif details
http://allinworld99.blogspot.in/2016/02/flow-chart-with-example-for-if-then.html

Answer 2

else if basically means the else part of if is another if statement.

Answer 3

Emphasizing what Gumbo said.

Also, if a language has a real elif / elsif / elseif (say, a "real" else-if instruction, instead of a kind of nested chaining hidden away by formatting), then the compiler can easly emit a single node in an Abstract Syntax Tree (or similar, see http://en.wikipedia.org/wiki/Abstract_syntax_tree) instead of nesting them.

To give an example:

Say in C/C++ you have:

if (a) {
    X
} else if (b) {
    Y
} else if (c) {
    Z
} else {
    0
}

Then the compiler will build an AST-node like this:

   a
  / \
 X   b
    / \
   Y   c
      / \
     Z   0

But if the language of choice has a real if-else:

if (a) {
    X
} elif (b) {
    Y
} elif (c) {
    Z
} else {
    0
}

Then the AST could more easily look like this:

   (a--b--c)
   /  /  /  \
  X  Y  Z    0

In such a language, an "if else" would only be possible if braces are not mandatory:

if (a) {
    X
} elif (b) {
    Y
} else if (c) {  // syntax error "missing braces" if braces mandatory
    Z
} else {
    0
}

Corresponding AST (if braces are not mandatory):

   (a--b)
   /  /  \
  X  Y    c
         / \
        Z   0

This could make CFG-Analysis (http://en.wikipedia.org/wiki/Control_flow_graph) easier to implement (though there might be no actual optimization benefit; so imho it'd just benefit the lazy programmer :D).

Answer 4

You already gave the answer yourself. if/else is for true/false result, like is an int=2 or any other possible int value, and if/elseif is for more than 2 results, like an int=2, and int=3 and so on.

Also it groups the context of a variable. You could check every single result like

if (a == 2) { do one thing };
if (a == 3) { do another thing };
...
if (a != 2 && a != 3 ...) { do something else };

With if/else/elseif it's better readable.