If else syntax. Conditional if statement in PHP
Ability to control program flow allows for selective execution individual areas code, and this is a very valuable programming feature. The if statement allows us to execute or not execute certain sections of code, depending on whether the statement's condition is true or false. One of the most important purposes of the if statement is that it allows the program to take action based on what the user has entered. A trivial example of using if is checking the password entered by the user; if the password is correct, the program allows the user to perform some action; if the password is entered incorrectly, then the program will not allow the user to access limited resources.
Without the conditional statement, the program would execute the same way over and over again, no matter what input the user gave. If you use selection operators, the result of the program can be much more interesting, since it will depend directly on the user’s input data.
Before you begin to understand the structure of the if statement, it is worth paying attention to the meanings TRUE and FALSE in the context of programming and computer terminology.
The true value (TRUE) has a value other than zero, FALSE is equivalent to zero. When using comparison operators, the operator will return one if the comparison expression is true, or - 0 if the conditional expression is false. For example, the expression 3 == 2 will return the value 0, since three does not equal two. The expression 5 == 5 evaluates to true and will return the value 1. If you have trouble understanding this, try printing these expressions to the screen, for example: printf("%d", 7 == 0);
During the programming process, you often have to compare some variables with others and, based on these comparisons, control the program flow. There is a whole list of operators that allows you to perform comparisons, here it is:
You're probably familiar with these comparison operators, but just in case, I've shown them in the table above. They should not be difficult for you to understand; most of these operators you learned in school in mathematics lessons. Now you understand what TRUE and FALSE are, it's time to put the if select statement to the test. if structure:
If (conditional expression) // here is one statement that will be executed if the conditional expression is true
Here's a simple example of using the if statement:
If (7 > 6) printf("Seven is greater than six");
In this example, the program evaluates the conditional expression - “is seven greater than six?” To see the result of this piece of code, simply paste it into the main() function and do not forget to include the stdio.h header, run the program and see the result - true. Construction of the selection operator if with curly braces:
If (TRUE) ( /* all code placed inside the brackets will be executed */ )
If you do not use curly braces, then only one, the first statement, will relate to the body of the if statement. If you need to control several operators, you need to place them in curly braces. I recommend always putting parentheses after the if declaration - this is good tone programming and you will never get confused in your code, since this declaration is the most understandable.
else operator
Sometimes, when a conditional expression is FALSE, it would be convenient to have some code executed that is different from the code that is executed when the condition is TRUE. How is this done?
Here is an example of using the if else statement:
If (TRUE) ( /* execute this code if the condition is true */ ) else ( /* execute this code if the condition is false */ )
else if construct
Typically, else if statements are used when multiple selection is needed, that is, for example, several conditions are defined that can be true at the same time, but we only need one true conditional expression. You can use the if else statement immediately after the if statement, after its body. In such a case, if the condition of the first select statement is TRUE, then the else if clause will be ignored, whereas otherwise, if the condition of the first select statement is FALSE, the check in the else if clause will begin to be executed. That is, if the condition of one if statement is true, then the others will not be checked. Now, in order to firmly consolidate all this in our heads and understand it, let’s look at a simple example using selection operator constructs.
#include
Let's look at interesting conditional expressions using logical operators.
Logical operators allow you to create more complex conditional expressions. For example, if you want to check whether your variable is greater than 0 but less than 10, then you just need to use the logical operator - AND. This is how it is done - var > 0 and var< 10 . В языке СИ есть точно такой же же оператор, только обозначается он иначе — && .
When using if statements, it is often necessary to test multiple various conditions so it is very important to understand the logical operators OR, NOT and AND. Logical operators work exactly the same as comparison operators: they return 0 if false or 1 if logical expression- true.
You can read more about logical operations in.
Hi all. And today I want to tell you about if and else conditions. I’m just sure that almost everyone who is reading this now knows perfectly well what we’re talking about. Well, for everyone else, I’ll explain it better.
And so if - is translated from in English as "If", while else is otherwise. Let me show you an example right away and I think everything will immediately become clear to many.
$a = 1;
if ($a == 1) (
echo "a = 1";
) else (
echo "a is not equal to 1";
} ?>
I think many have already guessed that the result of this example will be the appearance of “a = 1” on the screen. And all because we assign the value 1 to variable a at the very beginning. That is. If we have the correct value in brackets after if, then the script located in the first curly brackets () is executed. Otherwise (else) Execute from other brackets, here is another example.
$a = 2;
if ($a == 1) (
echo "a = 1";
) else (
echo "a is not equal to 1";
} ?>
This example will show that a does not equal one. But in fact, these are basic, but simple structures. PHP also has a more compact option for writing conditions.
The result of this example will be exactly the same as in the examples above. Also, don’t forget one more design
if ($a == 1):?>
Our a again has the value 1
And now a more complex design
I'll even start right away with examples.
if ($a >= 0) (
if ($a == 0) (
?>
Our A is zero
Our A Above zero
) else (
echo "Our variable is less than zero=(";
}
?>
As you can see, you can also put other conditions into conditions; you can create as many of them as you like.
And here's another example for you.
if ($a == 0)(
echo "Variable is null";
) elseif ($a > 0 && $a<5) {
?>
And more than zero, but definitely less than 5
= 5 || $a == -5)(
echo "You will see this test only if A is greater than or equal to 5. OR!! If A is equal to -5";
)else(?>
And you will see this if a is less than zero, and at the same time NOT equal to -5.
In fact, in the last example in the last else there is no such condition that $a should not be equal to -5. It’s just that if a is -5, then the condition that was above will be fulfilled and will not have time to reach the lower one.
And also, if you still don’t understand, the conditions that are written in parentheses use special operators; they are discussed in another article. But fortunately there are not many of them and I can repeat them right here.
Logical operators that are used in conditions
Equality, not to be confused with assignment (=), for example $a = 1; - In this case, we put one in cell “a”, and the entry is like $a == 1, the same as 1 == 1.
Not equality. if(1 != 2)(echo "This condition will definitely work because 1 is not equal to 2"; )
|| - OR. By the way, if anyone enters these 2 characters if in the English layout they press Shift + forward slash (under the backspace).
0 || $a< 0){echo "Это условие сработает если А будет равняться например -15 ИЛИ например 23 "; }?>
By the way this example you can write it like this
&& - AND. With this logical operator, the script will be executed only if both conditions are met.
0)( echo "For this, A must not be zero AND must be greater than zero"; )?>
Here's the same example
0 ? "Is it greater than zero" : ""?>
I just told you how to use logical operators, but there is one more thing! What some programmers actually forget about.
$a = 1;
if($a)(
echo "It will be executed because we have $a and it is not empty. But if we write $b in the condition, then else will already be executed, because we don’t have $b =(";
)else(
echo "We will always have the first condition met because we always have A";
}?>
The bottom line is that when checking conditions, true or false is returned. If you look at the top example. There is no way we can NOT have emptiness in the if condition. Any emptiness or if the logical operator does not pass, false is returned, otherwise true is returned.
if($a = 1)(
echo "It will always be true! Because the assignment of the variable "a" to a value occurs directly in the condition, i.e. we will assign one, and only then it will be checked if there is something in the variable $a. And of course, if we now output $a , then we will see ".$a;
)else(
echo "We'll never get here=(";
}?>
I guess I'll end here. Good luck to everyone, remember the most important thing, this was PHP and therefore this section of code should be located in. Of course, read my blog, in which I will tell you how to still write great websites and web applications. And even how not only to write them, but how to do it correctly!
Conditional operator allows you to skip or execute a certain block of code depending on the result of calculating the specified expression - condition. A conditional statement can be said to be a decision point in a program; sometimes it is also called a branch statement. If you imagine that the program is a road, and PHP interpreter- a traveler walking along it, then conditional statements can be thought of as intersections where the program code branches into two or more roads, and at such intersections the interpreter must choose which road to follow next.
if statement
The if statement is the simplest of the branch statements.
The syntax of the if statement is:
The if statement first evaluates the conditional expression specified in parentheses, the result of which is a Boolean value. If the result obtained is true, then the instruction is executed. If the expression returns false, then the instruction is not executed. An expression of any complexity can be used as a condition.
If the body of the if statement uses only one instruction, then enclosing it in curly braces is possible, but not required. However, if you need to execute more than one instruction in the body of an if statement, then these several instructions must be enclosed in curly braces. Please note that there should not be a semicolon after the closing curly brace.
The following code demonstrates the use of the if statement:
If statements can be nested within other if statements:
Pay attention to the last example: the instruction does not have to be written exactly under the if statement; if the instruction is not large in size, then it can be written in one line.
if else statement
And so we learned that the if statement allows you to execute instructions if the condition is true. If the condition is false, then no action is performed. However, it is often necessary to execute certain instructions if a certain condition is true and other instructions if the condition is false. It is for such cases that if else branching is used. It consists of an if statement followed by a block of statements and keyword else followed by another block of statements.
The syntax of the if else statement is:
The else statement is optional. The block of instructions located after else is executed by default, i.e. when the conditional expression in if returns false . The else statement cannot be used separately from the if statement. The else block should only appear after the if statement; it can be considered the default action.
Modifying our previous example slightly, we can see how the if else statement works if the condition returns false:
The if else statement can be nested. Such nested conditional statements occur quite often in practice. An if statement is nested if it is nested inside another if or else block. If your code uses multiple if statements in a row, the else always refers to the closest if:
The last else does not apply to if($a) since it is not in indoor unit, so the closest one to it is if($i) . The else statement inside the block is related to if($b) because this if is the closest one to it.
elseif/else if construct
The if/else statement evaluates the value of a conditional expression and executes a particular fragment program code. But what if you need to execute one of many fragments? If you need to check several conditions in a row, then the elseif or else if construction is suitable for this (this is the same construction, just written differently). Formally, it is not an independent PHP construct - it is just a common programming style that consists of using repeated if/else statements. It allows you to check additional conditions until true is found or the else block is reached. elseif/else if construct must be placed after the if statement and before else operator, if there is one.
Here three conditions are checked and, depending on the value of the $username variable, different actions are performed.
There's really nothing special about this piece. It is simply a sequence of if statements, where each if statement is part of the else clause of the previous if statement. For those who have encountered this form of notation for the first time and do not really understand how it works, we will rewrite the same example, only in an equivalent syntactic form that fully shows the nesting of structures:
Consistent execution is so common that we rarely remember it as a control structure. The sequence of statements is executed in the order of their natural location in the program, with a possible deviation to call an external fragment (function), but with a mandatory return to the point of call.
In the simplest case, branching is described in the C language using a conditional operator. having the form:
| if (expression) operator_1; else operator_2; |
where is the part else may be absent. First the "expression" is evaluated in brackets; if it is true then it is executed operator_1. If " expression" false (equal to zero - NULL), That operator_1 is skipped and executed operator_2. If in place of conditionally executed operators there should be a group of several language operators, then they are enclosed in curly braces - { }. Often the "expression" in parentheses represents a condition specified using relational and logical operators. Relational operations are denoted in C as follows:
= = equal; ! = not equal;< меньше; >more;
< = меньше или равно; >= greater than or equal to.
Symbol !
in C language denotes logical negation. There are two more logical operations: ||
means or &&
- logical AND. Relational operations take precedence over arithmetic operations, so an expression of the form k > n%i calculated as k > (n%i). A priority &&
higher than ||, but both logical operations are performed after relational and arithmetic operations. In doubtful cases, it is better to use parentheses.
To illustrate the use of the conditional operator, consider a program to determine the largest of three numbers. First if the operator represents a complete conditional construction, in the second case else absent. Note that the semicolon ends the assignment statement max=x, does not violate unity if- operator. If else- the branch is skipped in nested conditions, their interpretation may be ambiguous. To avoid ambiguity, solve it this way: else matches the nearest if, not having his own else.
Example 1.3.
Let's look at an example of a program that uses several nested conditional statements. In this program there is a line float A, B, X declares these three variables as real values. Function format string scanf instructs you to enter two real numbers, which will become the values of the variables A and B respectively.
Example 1.4
| /*SOLUTION OF EQUATION AX=B*/ #include main() { float A,B,X; |
See what branching looks like when the nesting depth of conditional statements is three (Example 1.5). If at least one condition is true, then all the remaining ones are, of course, skipped. When the nesting depth of conditional statements exceeds three, branching loses clarity and clarity.
To implement multitasking branching, they usually resort to a control structure choice ( switch) (see paragraph 9.4). When the branch control structure becomes particularly confusing, curly braces can provide some clarity. They are required when a conditional statement contains more than one statement or function, for example
Last update: 07/30/2016
Conditionals are one of the basic components of many programming languages, which direct the program to work along one of the paths depending on certain conditions.
The following conditional constructs are used in the C# language: if..else and switch..case
if/else construct
The if/else construct checks the truth of a certain condition and, depending on the results of the check, executes certain code:
Int num1 = 8; int num2 = 6; if(num1 > num2) ( Console.WriteLine($"Number (num1) is greater than number (num2)"); )
The if keyword is followed by a condition. And if this condition is met, then the code that is placed further in the if block after curly braces. The previously discussed comparison operations serve as conditions.
IN in this case we have the first number greater than the second, so the expression num1 > num2 is true and returns true , therefore, control passes to the line Console.WriteLine("The number (num1) is greater than the number (num2)");
But what if we want some action to also be performed if a condition is not met? In this case we can add an else block:
Int num1 = 8; int num2 = 6; if(num1 > num2) ( Console.WriteLine($"The number (num1) is greater than the number (num2)"); ) else ( Console.WriteLine($"The number (num1) is less than the number (num2)"); )
Int num1 = 8; int num2 = 6; if(num1 > num2) ( Console.WriteLine($"The number (num1) is greater than the number (num2)"); ) else if (num1< num2) { Console.WriteLine($"Число {num1} меньше числа {num2}"); } else { Console.WriteLine("Число num1 равно числу num2"); }
We can also connect several conditions at once using logical operators:
Int num1 = 8; int num2 = 6; if(num1 > num2 && num1==8) ( Console.WriteLine($"Number (num1) is greater than number (num2)"); )
In this case, the if block will be executed if num1 > num2 is true and num1==8 is true .
Switch construction
The switch/case construct is similar to the if/else construct, as it allows you to process multiple conditions at once:
Console.WriteLine("Press Y or N"); string selection = Console.ReadLine(); switch (selection) ( case "Y": Console.WriteLine("You pressed the letter Y"); break; case "N": Console.WriteLine("You pressed the letter N"); break; default: Console.WriteLine(" You pressed an unknown letter"); break; )
After the switch keyword, the expression to be compared comes in parentheses. The value of this expression is sequentially compared with the values placed after the case operator. And if a match is found, then a specific case block will be executed.
At the end of each case block, one of the transition operators must be placed: break , goto case , return or throw . Typically, the break statement is used. When it is used, no other case blocks will be executed.
However, if we want, on the contrary, after the execution of the current case block, another case block is executed, then we can use the goto case statement instead of break:
Int number = 1; switch (number) ( case 1: Console.WriteLine("case 1"); goto case 5; // go to case 5 case 3: Console.WriteLine("case 3"); break; case 5: Console.WriteLine( "case 5"); break; default: Console.WriteLine("default"); break; )
If we also want to handle the situation where no match is found, we can add a default block, as in the example above.
Using the return statement will allow you to exit not only the case block, but also the calling method. That is, if in the Main method after the switch..case construction, which uses the return statement, there are any operators and expressions, then they will not be executed, and the Main method will complete its work.
The throw operator is used to throw errors and will be discussed in one of the following topics.
Ternary operation
The ternary operator has the following syntax: [first operand - condition] ? [second operand] : [third operand] . There are three operands here. Depending on the condition, the ternary operator returns a second or third operand: if the condition is true , then the second operand is returned; if the condition is false , then the third one. For example:
Int x=3; int y=2; Console.WriteLine("Press + or -"); string selection = Console.ReadLine(); int z = selection=="+"? (x+y) : (x-y); Console.WriteLine(z);
Here the result of the ternary operation is the variable z. If we enter “+” above, then z will be equal to the second operand - (x+y). Otherwise z will be equal to the third operand.