(i) The switch-case statement is an alternative to if... elseif... else statement which does almost the same thing.
(ii) The switch-case statement tests a variable against a series of values until it finds a match, and then executes the block of code corresponding to that match.
(iii) The switch statement executes line by line, unlike if... elseif...else.
(iv) It also executes all the subsequent case statement till the end of the switch block automatically.
(v) To prevent this add a break statement to the end of each case block.

(i) In if...else if...else statements, more than one block of statement can execute based on the condition and user needs.
(ii) If we want to check for another condition in the else part, choose if... elseif ... else statement
(iii) Unlike else, it will execute that alternative expression only if the elseif conditional expression evaluates to "True value.

(i) Conditional statements are useful for writing decision making logics. It is the most important feature of many programming languages, including PHP.
(ii) When we write the code for conditional statements very often, we can perform different actions for different decisions in different business logic.

If else statement in PHP:
If statement executes a statement or a group of statements if a specific condition is satisfied by the user expectation. When the condition gets false (fail) the else block is executed.
Syntax:
if (condition)
{
Execute statement(s) if condition is true;
}
else
{
Execute statement(s) if condition is false;
}
Example
＄Pass_Mark=35;
＄Student_Mark= 70;
if (＄Student_Mark>= ＄Pass_Mark){
echo "The Student is eligible for the promotion";
}
else {
echo "The Student is not eligible for the promotion";
} ?>

Switch Statement:
(i) This is a multiple branching statement where, based on a condition, the control is transferred to one of the many possible points.
(ii) The switch statement is used to specify multiple conditions. It runs a different code block for different conditions.
Syntax
switch (expression)
{
case value1:
      //code to be executed if expression = value1; break;
case value2:
      //code to be executed if expression = value2; break;
...
default:
      //code to be executed if expression is not equal to any of the values;
}
Example:
    ＄x = 10;
     switch (＄x)
     {
          case 5:
               echo "x is equal to 5";
                break;
           case 10:
                echo "x is equal to 10";
                 break;
            case 15:
                 echo "x is equal to 15";
                  break;
             default:
                  echo "x is not equal to 5, 10, or 15";
           }
?>
Output:
x is equal to 10

(i) If statement in PHP: If statement executes a statement or a group of statements if a specific condition is satisfied as per the users expectation. This is the simplest PHP's conditional statement and can be written in the following form.
Syntax:
if (condition)
{
     // code to be executed if condition is true;
}
(ii) If else statement in PHP: The if statement evaluates a condition and executes a set of code if the condition is true and another set of code if the condition is false.
Syntax:
if(condition)
{
       //True-block;
}
else
{
       //False-block;
}
(iii) If-elseif-else statement in PHP: If-elseif-else statement is a combination of if-else statement. Here multiple conditions can be checked and action is based on the result of the condition.
Syntax:
if (Condition 1)
{
          //code to be executed if condition 1 is true;
}
elseif (condition2)
{
         //code to be executed if condition1 is false and condition2 is true;
}
elseif (condition3)
{
         // code to be executed if condition1 and condition2 are false and condition3 is true;
}
else
{
         //code to be executed if all conditions are false;
}
Switch case: The switch case is an alternative to the if.. elseif.. else statement which executes a block of code corresponding to the match.
Syntax:
switch (expression)
case value1:
           //code to be executed if expression= value1; break;
case value2;
           //code to beexecuted if expression = value2; break;
...
default:
           //code to be executed if cexpression is not equal to any of the values;
}