how to code a php switch statement with variables from input code example

Example 1: php switch

$age=20;
switch ($age) {
	case 19:
        echo "Age is 18";
        break;
    case 20:
        echo "Age is 20";
        break;
    case 21:
        echo "Age is 21";
        break;
}

Example 2: php switich

switch (n) {
    case label1:
        code to be executed if n=label1;
        break;
    case label2:
        code to be executed if n=label2;
        break;
    case label3:
        code to be executed if n=label3;
        break;
    ...
    default:
        code to be executed if n is different from all labels;
}