Function declaration
A function declaration is a source-language construct that specifies a function’s name and parameter interface, and may include its implementation.
Secrets of the JavaScript Ninja, Second Edition
A JavaScript statement that defines a named function.
- How it is used
- Defines named JavaScript functions as standalone statements, distinguishing them from function expressions when deciding where a function is available for invocation.
- How deep it goes
- Explains required syntax, nesting, and early identifier registration in lexical environments, while deferring detailed scope and identifier resolution.
- Examples
- Compares nested declarations with function expressions and tests access to a function before its declaration executes.
- What you can do after
- Build it from scratch as a named statement and predict when calls before its declaration work in global or function environments.
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A Pythonic Adventure: From Python basics to a working web app
A function definition is a Python statement that declares a function's name, arguments, and indented body.
- How it is used
- Defines reusable menu behavior so one operation can serve drinks, flavors, and toppings.
- How deep it goes
- Explains def syntax, arguments, indentation, return values, default arguments, and calls through a menu program.
- Examples
- Uses a coffee-shop menu with drink, flavor, and topping lists, including interactive selections and printed orders.
- What you can do after
- Build it from scratch: declare a menu function, call it with different lists, and return each selected item.
Modern C
A function declaration is a C declaration that specifies a function's name, parameter interface, and return type without necessarily defining its body.
- How it is used
- Identifies a function and its interface before distinguishing that declaration from its definition and calls.
- How deep it goes
- Defines the distinction through `main` and its braced body, while deferring complications in the declaration–definition relationship.
- Examples
- Uses `int main(void)` followed by a braced body and contrasts it with a call to `printf`.
- What you can do after
- Evaluate/understand whether a function is merely declared or also defined by checking for its braced body.
Get Programming: Learn to code with Python
A function definition is a Python construct that declares a function's name, parameters, and executable code block.
- How it is used
- Defines reusable Python modules that accept values, perform an action, and return a value.
- How deep it goes
- Explains syntax, indentation, docstrings, calls, returns, and function scope, but stops short of deeper implementation details.
- Examples
- Uses attendance checking, string concatenation, quick-check definitions, and a tip-calculation exercise.
- What you can do after
- Build it from scratch by defining functions, documenting them, calling them with values, and using returned results.
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Modern C, Third Edition
A function definition is a C construct that specifies a function's declaration and body.
- How it is used
- Distinguishes function declarations from definitions and identifies main as the starting point of program execution.
- How deep it goes
- Explains the distinction through declarations, return types, parameter lists, function bodies, and enclosing braces.
- Examples
- Uses main(void) and main with argc and argv to show declarations followed by executable function bodies.
- What you can do after
- Evaluate whether a function name has only a declaration or a complete definition containing a body.
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Learn AI-Assisted Python Programming, Second Edition
- How it is used
- Uses function declarations to organize reusable input-processing-output tasks and prompt Copilot to generate Python code.
- How deep it goes
- Explains function headers through their keyword, name, inputs, colon, body, and returned output.
- Examples
- Uses a larger function that compares two numbers, alongside the mathematical example f(x) = x².
- What you can do after
- Build it from scratch by writing a Python function header, defining its body, and returning a result.
Read how Learn AI-Assisted Python Programming, Second Edition explains function declaration →
Related concepts
- function expressioncontrasts with · A function expression is an expression that creates a function value, which can be assigned, passed, or used within another expression.
- inputhas part · An input is a value, information, or signal supplied to a system, computation, or interface for processing or to influence its behavior.
- declarationcontrasts with · A declaration is source syntax that introduces a program entity and specifies its name, type, or other properties without necessarily defining it or assigning a value.
- function parameterhas part · A function parameter is a named input declared in a function definition that receives a corresponding argument value when the function is called.
- functionpart of · A function is a callable program unit that performs an operation, may accept inputs, and can produce a result or side effect.
- return typehas part · A return type is the declared or inferred type of the value that a function or method supplies to its caller.
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