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Parameter (computer programming)
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<p>In <a href="/facts/Computer_programming/QmSsFnu0">computer programming</a>, a parameter, a.k.a. formal argument, is a <a href="/facts/Variable_(computer_science)/VoCKtwml">variable</a> that represents an argument, a.k.a. actual argument, a.k.a. actual parameter, to a <a href="/facts/Subroutine/9vFJrg0A">subroutine</a> call.. A function's <a href="/facts/Function_signature/psEPS0UW">signature</a> defines its parameters. A call invocation involves evaluating each argument expression of a call and associating the result with the corresponding parameter. </p><p>For example, consider subroutine def add(x, y): return x + y. Variables x and y are parameters. For call add(2, 3), the expressions 2 and 3 are arguments. For call add(a+1, b+2), the arguments are a+1 and b+2. </p><p>Parameter passing is defined by a programming language. <a href="/facts/Evaluation_strategy/Pc9kLWgs">Evaluation strategy</a> defines the semantics for how parameters can be declared and how arguments are passed to a subroutine. Generally, with <a href="/facts/Call_by_value/Pc9kLWgs">call by value</a>, a parameter acts like a new, local variable initialized to the value of the argument. If the argument is a variable, the subroutine cannot modify the argument state because the parameter is a copy. With <a href="/facts/Call_by_reference/Pc9kLWgs">call by reference</a>, which requires the argument to be a variable, the parameter is an alias of the argument. </p>