An Overview of C Functions
Code Modularization Requires User-Defined Functions: Functions enable you to divide your code into logical operations, improving readability and enabling code reuse. Programs can be modularized in C by combining prefabricated C standard library routines with newly written ones. Using prefabricated functions makes your work easier.
Among the reasons people use functions are:
- The divide-and-conquer strategy facilitates the management of program development. Decomposing a difficult problem into smaller, more manageable components and creating a function for each is preferred. A lengthy C program becomes easier to read and manage when it is broken up into smaller chunks.
- Creating new programs by utilising pre-existing features. Reusability of such software is a fundamental idea. By using functions, you can avoid writing the same code over and over. Packing a chunk of code as a function enables it to be called from other program locations if it is required more than once. Despite being run numerous times, the function’s code is only kept in one location in memory.
- Standardised functions that carry out particular duties can be used to develop programs if they are properly named and defined. This is referred to as abstraction.
- Writing programs and monitoring their actions are made simpler by the use of functions. Each activity can be created and checked more or less independently if the program action can be broken down into distinct activities and placed in a separate function. Code division into modular functions facilitates program design and comprehension.
- Numerous program statements are grouped together and given a name by functions.
- A function is a self-contained block of statements that can be executed and carry out a specific activity. A program should be divided into discrete parts, with functions written for each of these parts.
Function Declaration, Function Definition, and Prototyping: You need to define, call, and declare a user-defined function in order to use it.
Function Definition
The function body’s code is provided by the function definition. It is a stand-alone program module created to carry out the specifications of the function. The definition of a function must be made exactly once. A function definition in C typically has the following format: returnType name (parameters of type1, type2, ProgramStatement { variableDeclarations… return expression; }. The two parts of a function definition are the header and the body. The definition’s parameters are sometimes referred to as formal parameters.
Function Declaration (Prototype)
In C, a function and its prototype should be declared before the function is defined. The name, return type, number, types, and order of the parameters that the function expects are all declared in a function prototype. To make sure the calling code is utilising the correct kinds to call the function, the compiler type-checks it using the prototype.
Because they make error checking between calls and definitions easier, function prototypes are preferred. Additionally, they support the compiler’s automated type conversions of function parameters. The ANSI Prototype function declaration in C is generally expressed as data_type function_name (type1 arg1, type2 arg2 – – – – );. A function should have the keyword void in the parameter-list if it receives no parameters. The function type is void if the function returns nothing. An identifier may be declared more than once, but it may only be defined once. All functions should be declared at the beginning of main().
Function Return Values and Types
A function can give the caller function a value in return. The data type, also known as the return-value-type, describes the kind of data that a function will return. Except for arrays, any of the data types listed in C can be returned by a function. In C, if no return type is given, a User Defined Function’s (UDF) default return type is int.
A function uses a return statement to give back a value. The return statement returns control to the calling environment after ending the function’s execution. The value of any expression in the return statement is returned. Only one value can be returned by a function at once. Only one return statement will be executed, even if it may contain several.
When the function’s last right brace is reached, or by running the return; statement, control returns if the function does not return a value.
Code Example Illustrating Return Values and Types:
#include <stdio.h>
// Function prototype declaring the return type (int) and argument types (int, int)
int sum(int a, int b);
int main() {
int x = 5;
int y = 7;
int z = 0;
// Call the sum function, receive the returned value, and store it in z
z = sum(x, y);
// Print the value returned by the sum function
printf("Sum of %d and %d is: %d\n", x, y, z);
// Another example: calling sum and passing the result directly to printf
printf("Sum of %d and %d is: %d\n", 8, 12, sum(8, 12)); // The return value 20 is passed to printf
return 0; // main returns 0 indicating successful execution
}
// Function definition: calculates the sum of two integers and returns it
int sum(int a, int b) {
int tmp = 0;
tmp = a + b;
return tmp; // Returns the integer value stored in tmp
}Output of the code example:
Sum of 5 and 7 is: 12
Sum of 8 and 12 is: 20Function Calls and Call-by-Value
A function call invokes a function. In addition to providing the function name, a function call also supplies the parameters that the function requires. Control moves from the point of invocation to the called function when a program encounters a function call. The statements of the called function then run, and control then returns to the caller. The statement of the function that called it always receives value or control back from the function. Anyone can call any other function in C.
The function call/return is supported by the function-call stack, which is an essential mechanism. Each function pushes a stack frame onto the stack as it is invoked. This stack frame includes the return address required by the called function. Control moves to the return address and the stack frame is popped when a called function returns.
Call by value is one way to send arguments to a function when calling it. Sending values to functions is known as “call by value.” When an actual argument is used to pass a value, the function copies the value of the actual argument. As a result, in the function, the value of the appropriate formal argument can be changed, but in the calling routine, the value of the real parameter remains unchanged.
The following C code example illustrates call by value:
#include <stdio.h>
void try_to_change_it(int a_copy) {
// a_copy is a copy of the argument passed from main
a_copy = 777;
printf("Inside function: a_copy = %d\n", a_copy); // 777 is printed
}
int main(void) {
int a = 1;
printf("Before function call: a = %d\n", a); // 1 is printed
try_to_change_it(a); // Pass the value of a
printf("After function call: a = %d\n", a); // 1 is printed again!
return 0;
}Output of the code example:
Before function call: a = 1
Inside function: a_copy = 777
After function call: a = 1An evaluation of the expression a yields a value that is a copy of a when an is supplied as an argument. The function try_to_change_it is passed this copy instead of a copy of itself. Therefore, the variable an is not altered in the calling context (main).
Function Types
The value that a given function returns and the type of parameter value can determine which functions fall into which categories. Whether a function returns values or accepts arguments determines its classification.
The sources outline the following classifications:
- Function with No Argument and No Return Value: Functions that don’t accept or return any values from the caller function are known as functions with no arguments or return values.
- Print_message() in this example indicates no return value and no arguments with its void return type and void parameter list.
- Function with Argument but No Return Value: These methods take in arguments from the user but don’t provide back any data. The “Argument with No Return” category is mentioned.
- Although it has a void return type, this example of the hexadecimal function from the sources accepts an integer input (c1).
- Function with Arguments with Return Value: This type of communication involves two parties; arguments are passed to a function, and it returns a value.
- This example demonstrates a function sum that accepts two integer inputs and returns an integer value; it is comparable to the example given in the sources.
- Function with No Argument but Return Value: Functions that do not accept arguments but instead give the caller a value fall under this category.
- The function get_pi in this example, as described in the sources, produces a float value but accepts no parameters.
UDFs stand for user-defined functions.
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