CODEWITHSUNDEEP
c++if-statement
H4cKL0rD
H4cKL0rD

Reputation: 5508

Why use if-else if in C++?

Why would you use if-else statements if you can make another if statement?

Example with multiple ifs:

input = getInputFromUser()
if input is "Hello"
    greet()

if input is "Bye"
    sayGoodbye()

if input is "Hey"
    sayHi()

Example with else-if:

input = getInputFromUser()
if input is "Hello"
    greet()

else if input is "Bye"
    sayGoodbye()

else if input is "Hey"
    sayHi()

Upvotes: 1

Views: 23560

Answers (5)

Uzair Nadeem
Uzair Nadeem

Reputation: 745

Following your same example if we use sequence of if conditions, whatever the input is it will run all 3 conditions. Replacing sequence of if with if-else conditions will run only first condition in best case whereas all 3 in worst case.

So conclude with that if-else will save our running time in most cases, therefore using if-else is preferred over using sequence of if conditions. 

input = getInputFromUser()
if input is "Hello"
    greet()

if input is "Bye"
    sayGoodbye()

if input is "Hey"
    sayHi()

Upvotes: 0

Brian Postow
Brian Postow

Reputation: 12187

If you have non-exclusive conditions:

if(a < 100)
{...}
else if (a < 200)
{...}
else if (a < 300)
....

this is very different from the same code without the "else"s...

Upvotes: 13

Michael Stum
Michael Stum

Reputation: 180944

It's also more performant.

In your first example, every if will be checked, even if input is "Hello". So you have all three checks.

In your second example, execution will stop once it found a branch, so if the user types "Hello" it will be only one check instead of three.

The difference may not be much in your simple example, but imagine that you're executing a potentially expensive function and you might see the difference.

Upvotes: 13

Tadeusz Kopec for Ukraine
Tadeusz Kopec for Ukraine

Reputation: 12413

If you need to chose exactly one action from given set of actions, depending on some conditions, the natural and most clear choice is either switch (don't forget to break after each branch) or combination of if and else. When I write

if (conditon1)
{
    action1();
}
else if (condition2) 
{
    action2();
}
else if (conditon3)
{
    action3();
}
.
.
.
else {
    action_n();
}

it is clear to the reader that exactly one of actions is to be performed. And there is no possibility that because of mistake in conditions more than one action is performed.

Upvotes: 7

Brad Cupit
Brad Cupit

Reputation: 6580

you mean like this:

if (a == true && b == false && c == 1 && d == 0) {
    // run if true
}

if (a == false || b == true || c != 1 || d != 0) {
    // else
}

An else-statement would be much clearer and easier to maintain.

Upvotes: 8

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