if
PROVIDES conditions for
DECISION TAKING at runtime when you have only one expression to evaluate.
Is a very important language construction, because it allows decision making during the programming process.
In PHP its structure is similar to the C language.
In the following, we will show the first type of conditional structure:
if .
SINGLE STATEMENT
In the following, we will show the SINGLE STATEMENT of - if - conditional structure:
<?php
// SINGLE EXPRESSION
// SINGLE STATEMENT
if (expr 1)
statement 1
where,
expr 1 = THE EXPRESSION TO BE EVALUATED
and
statement 1 = EXECUTED IF expr 1 evaluates to TRUE
IGNORED IF expr 1 evaluates to FALSE
?>
SINGLE STATEMENT (USUAL FORMAT)
In the following, we will show the SINGLE STATEMENT (USUAL FORMAT) of - if - conditional structure:
<?php
// SINGLE EXPRESSION
// SINGLE STATEMENT
if (expr 1)
{
statement 1
}
where,
expr 1 = THE EXPRESSION TO BE EVALUATED
and
statement 1 = EXECUTED IF expr 1 evaluates to TRUE
IGNORED IF expr 1 evaluates to FALSE
?>
if
The result of this conditional evaluation is always a BOOLEAN type.
The expr 1 will be evaluated:
01 . statement 1 will be executed...
If the expr 1 is verified as TRUE
02 . statement 1 ignored...
If every time expr 1 is verified as FALSE.
if ... else
PROVIDES conditions for DECISION TAKING at run time when you have two expressions to evaluate.
Is a very important language construction, because it allows decision making during the programming process.
In PHP its structure is similar to the C language.
In the following, we will show the second type of conditional structure: if ... else .
<?php
// TWO EXPRESSIONS
// TWO STATEMENTS
if (expr 1)
{
statement 1
}
else
{
statement 2
}
where,
expr 1 = Expression 1 to be EVALUATED
expr 2 = Expression 2 to be EVALUATED
and
statement 1 = Executed IF expr 1 evaluates to TRUE
statement 2 = Executed IF expr 1 evaluates to FALSE
?>
if ... else
The result of this conditional evaluation is always a BOOLEAN type.
The expr 1 will be evaluated:
01 . statement 1 will be executed...
If the expr 1 is verified as TRUE
02 . statement 2 executed...
If every time expr 1 is verified as FALSE.
if ... elseif ... else
PROVIDES conditions for DECISION TAKING at run time when there are more than two expressions to evaluate.
Is a very important language construction, because it allows decision making during the programming process.
In PHP its structure is similar to the C language.
In the following, we will show the third type of conditional structure: if ... elseif ... else .
<?php
// MORE THAN TWO EXPRESSIONS
// MORE THAN TWO STATEMENTS
if (expr 1)
{
statement 1
}
elseif(expr 2)
{
statement 2
]
elseif(expr 3)
{
statement 3
]
. . . . . . . . . . . .
else
{
statement N
}
where,
expr 1 = Expression 1 to be EVALUATED
expr 2 = Expression 2 to be EVALUATED
. . . . . . . . . . . . . .
expr N = Expression N to be EVALUATED
and
statement 1 = Executed IF expr 1 is checked as TRUE
statement 2 = Executed IF expr 1 is checked as FALSE and
expr 2 is checked as TRUE
. . . . . . . . . . . . .
statement N = Executed by DEFAULT - that is,
IF all PREVIOUSLY EVALUATED EXPRESSIONS
are checked as FALSE
?>
if ... elseif ... else
The result of this conditional evaluation is always a BOOLEAN type.
01 . statement 1 will be executed ...
If the expr 1 is verified as TRUE.
02 . statement 2 executed ...
If the expr 2 is verified as TRUE and the expr 1 is verified as FALSE.
03 . statement 3 executed ...
If expr 1 and expr 2 are FALSE and expr 3 is TRUE.
. . . . . . . . . . . . . . .
0N . statement N executed ...
if all of the above expressions are evaluated as FALSE.
Of course, there are other implementations, more complex and specific, for conditional evaluation.
Right now, what we teach you is enough.
We shall certainly return to the matter soon.