C Function Arguments/Parameters

In C programming, a function parameter is a variable or value that is passed to a function when it is called. These parameters provide input data to the function, which can then operate on them within its body. Function parameters play a critical role in enabling functions to be flexible, reusable, and capable of working with different inputs. There are different types of function parameters in C programming:

Function Parameters (or Formal Parameters)

Formal parameters are declared in the function's parameter list, and they act as placeholders for the values that will be passed to the function when it is called. The function uses these parameters to perform operations and computations.

Syntax:
return_type function_name(parameter_type parameter_name) { // Function body }
Example:
int add(int a, int b) { return a + b; }

Value parameters

Value parameters are the most common type of function parameter. When a value parameter is passed to a function, the value of the argument is copied into the parameter. This means that any changes made to the parameter inside the function will not be reflected in the argument outside the function.

For example, the following function takes a value parameter as input and returns the square of the parameter:

int square(int a) { return a * a; }

When the square() function is called with the argument 5, the value of 5 is copied into the parameter a. The square() function then returns the square of a, which is 25.

Reference parameters

Reference parameters allow you to pass the address of an argument to a function. This means that any changes made to the parameter inside the function will be reflected in the argument outside the function.

To declare a reference parameter, you use the & operator in front of the parameter type. For example, the following function takes a reference parameter as input and increments the value of the parameter by 1:

void increment(int& a) { a++; }

When the increment() function is called with the argument 5, the address of 5 is copied into the parameter a. The increment() function then increments the value at the address stored in a, which is 5. This means that the value of the argument outside the function will also be incremented to 6.

Pointer parameters

Pointer parameters are similar to reference parameters, but they allow you to pass a pointer to any type of data, not just variables.

To declare a pointer parameter, you use the * operator in front of the parameter type. For example, the following function takes a pointer parameter as input and prints the value of the data pointed to by the parameter:

void print_value(int* a) { printf("%d\n", *a); }

When the print_value() function is called with the argument 5, the address of 5 is copied into the parameter a. The print_value() function then prints the value of the data pointed to by a, which is 5.

Multiple Parameters

Functions can have multiple formal parameters, separated by commas, to accept multiple inputs.

float calculateAverage(float values[], int size) { // Function body }

Default Parameters (Not Supported in C)

Unlike some other programming languages, C does not support default parameters for functions. This means that all formal parameters must be provided with values when calling a function; there are no default values assigned to parameters if they are not provided.

Variable Arguments (Using <stdarg.h>)

In some cases, you may need to create functions that can accept a variable number of arguments. This is accomplished using variable arguments in C, typically implemented with functions like va_start, va_arg, and va_end from the <stdarg.h> library.

#include <stdio.h> #include <stdarg.h> int sum(int num, ...) { va_list args; va_start(args, num); int total = 0; for (int i = 0; i < num; i++) { total += va_arg(args, int); } va_end(args); return total; } int main() { printf("Sum: %d\n", sum(3, 5, 10, 15)); return 0; }
Explanation:

The sum function accepts a variable number of integer arguments. The va_list, va_start, and va_arg macros are used to iterate through the arguments.

Arguments (or Actual Parameters)

Actual parameters are the values or expressions that are provided when calling a function. They correspond to the formal parameters and supply the function with specific data to work on. Actual parameters are passed within the parentheses when calling a function. They can be constants, variables, expressions, or even the results of other function calls.

result = function_name(argument1, argument2);
Example:
int sum = add(5, 3); // '5' and '3' are actual parameters

Difference Between Arguments and Parameters in C

The terms "arguments" and "parameters" refer to different aspects of function usage. "Parameters" are variables defined in a function's declaration or definition and serve as placeholders for values that the function expects to receive when called. "Arguments," on the other hand, are the actual values or expressions provided to a function during its invocation, matching the parameters' order and data types.

While parameters define the function's interface and are used within the function's body, arguments supply specific values to be processed by the function, enabling it to perform its intended tasks.

Conclusion

Function parameters in C programming are variables or values passed to functions to provide input data. They are defined as formal parameters in the function's declaration and used as actual parameters when calling the function. C does not support default parameters, but variable arguments can be employed when a variable number of arguments is needed. Understanding these types of parameters is essential for creating flexible and versatile functions in C.






Related Topics
  1. Function return values in C
  2. Function Prototype in C
  3. main() Function in C
  4. Recursion in C
  1. Scope and Lifetime of a Variable in C
  2. Difference Between Arguments and Parameters in C