Else-If With Same Condition - if-statement

Question

if (Condition1)
{
dothis;
}
else if (Condition1)
{
dothat;
}
Out of curiosity, when I invoke the same condition for the else if, will the dothat part of the code still execute when Condition1 is satisfied? Does this vary from programming language to programming language?

Answer 1

What you wrote is basically equivalent to
if(Condition1)
{
dothis;
}
else
{
if(Condition1)
{
dothat;
}
}
So no, it will never be called.

Answer 2

No, the second condition will never be executed in any language. Here is a basic flowchart of your logic.
However, if Condition1 somehow evaluates to false in the first condition and true in the second, then the second will be called. Example:
<?php
$var = true;
function condition() {
global $var;
$var = !$var;
return $var;
}
if(condition()) {
echo "Conditional 1";
} elseif(condition()) {
echo "Conditional 2";
}
In this case, "Conditional 2" will be printed because condition() first evaluates to false, and then to true.

Answer 3

While at most one branch is executed1 per if-else-statement, in cases where the "condition" contains a a side-effect, it might not always be the if branch that is executed.
For instance, consider this JavaScript code with a side-effect introduced by the "condition" expression.
y = -1;
if (++y) { // the "condition" is ++y
alert("1")
} else if (++y) {
alert("2")
}
Only one branch ("2") was executed, but the same "condition" was used in both cases. For such reasons it can be problematic to have side-effects in conditionals.
1 In all modern mainstream languages the conditions for an if-else are evaluated "on demand" and "in order". Thus the first branch for which the condition evaluates to true is executed, regardless of other side-effects, and it is the only branch executed.

Answer 4

The second if follows an else – consequently, it will only be executed if the first if does not succeed. So – no; the dothat will not be executed. All (sane) programming languages do this.
However, some programming languages have special constructs for an else if, and you have to write it as one statement, variously called elif, elsif or ElseIf, depending on the language.

Answer 5

Since Condition1 evaluated to True the if's "dothis" will be invoked and skip over the else if. If you wanted to invoke the dothis and dothat then you would have two if statements with the same Condition1 or just put both dothis and dothat under one if statement. This is what I have seen in computer programming languages I have used.
Python example.
b = 2
if b == 2:
print "Hello"
elif b == 2:
print "World"
...
Hello