Control Structures (If then... else)

Hello.
Is it posiible to create a function using if (xxxx=A) then {do something} else {do something else} in a model or in a controller? The validation rules in a model operate in checking the input of a single field.
But in order to make a decision and control the flow of an app is something more  complicated. How is this done in Codeigniter?

See https://www.php.net/manual/en/control-structures.if.php

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