A function returns a value and control to calling function or code. A procedure returns the control but not any value to calling function or code. A procedure has support for try-catch blocks. A select statement can have a function call.
A function is like a procedure but it returns a value; its definition begins with a type name, e.g. int or double indicating the type of value it returns. Procedure calls are statements that get executed, whereas function calls are expressions that get evaluated.
A procedure is a routine that can accept arguments but does not return any values. A function is a routine that can accept arguments and returns one or more values.
A function returns a value and a procedure just executes commands.
The name function comes from math. It is used to calculate a value based on input.
A procedure is a set of commands which can be executed in order.
In most programming languages, even functions can have a set of commands. Hence the difference is only returning a value.
But if you like to keep a function clean, (just look at functional languages), you need to make sure a function does not have a side effect.
This depends on the context.
In Pascal-like languages, functions and procedures are distinct entities, differing in whether they do or don't return a value. They behave differently wrt. the language syntax (eg. procedure calls form statements; you cannot use a procedure call inside an expression vs. function calls don't form statements, you must use them in other statements). Therefore, Pascal-bred programmers differentiate between those.
In C-like languages, and many other contemporary languages, this distinction is gone; in statically typed languages, procedures are just functions with a funny return type. This is probably why they are used interchangeably.
In functional languages, there is typically no such thing as a procedure - everything is a function.
Example in C:
// function
int square( int n ) {
return n * n;
}
// procedure
void display( int n ) {
printf( "The value is %d", n );
}
Although you should note that the C Standard doesn't talk about procedures, only functions.
In general, a procedure is a sequence of instructions.
A function can be the same, but it usually returns a result.
There's a term subroutine or subprogram which stands for a parameterized piece of code that can be called from different places.
Functions and procedures are implementations of those. Usually functions return values and procedures don't return anything.
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