C Functions

Functions are blocks of code that can be reused within a program. They are stored under a name similar to a variable and can be called using this name.

Syntax

return_type name(parameters) {
  // Code goes here
}

Functions are declared with the following pieces:

• A return_type that denotes the specific type of data output.
• The name of the functions.
• The parameters are used for processing data in the function body, and the code for it to run in curly brackets.

A function named greet() that prints a greeting to the console can be declared like this:

void greet(void) {
  puts("Howdy!");
}

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The greet() function uses a void type to indicate that no output is returned after execution.

Calling a Function

After a function is declared, it can be called in the program. The syntax for this is the variables name followed by parenthesis.

#include <stdio.h>

// Declaring the function

void greet(void) {
  puts("Howdy!");
}

// Calling the function inside main()

int main() {
  greet();
}

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The output would be:

Howdy!

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Arguments

The values passed to a function are known as arguments. They represent the actual input values that can be used within the function.

#include <stdio.h>

void max(int x, int y) {
  if (x > y)
    printf("%d is the bigger number\n", x);
  else
    printf("%d is the bigger number\n", y);
}

int main() {
  int a = 20;
  int b = 30;

  max(a, b);

  return 0;
}

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Here’s another example:

#include <stdio.h>

void greet(char* name) {
  printf("Howdy %s!\n")
}

int main() {
  greet("John Doe"); // Output: Howdy John Doe!
  return 0;
}

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Returning Values

A function is also capable of returning a value back to were it was called using the return keyword. This is useful for computing values within a function. Notice that the word proceeding the function name indicates the type of value returned.

#include <stdio.h>

int add(int a, int b) {
  return a + b;
}

int main(void) {
  int num = add(1, 1);
  printf("%d\n", num);
}

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Here, the add() function has a return value of int.