Lesson 8.3. Void keyword

Definition

This keyword void is used when a function returns no value or accepts no parameters. Here is an example of a function with void:

int main (void) {
  return 0;
}

Function without returned value

When a function does not return a value, then the keyword void must be prefixed to its declaration. Here is an example of a function that displays an integer and returns nothing:

void println(int n) {
  printf ("%d\n", n);
}

In this type of function, the return keyword can be used, but it is only used to end the execution of the function.

Function without parameters

If a function accepts no arguments, you must specify void between the parentheses to inform the compiler (and the users) that it does not receive any parameters. For example, the standard function rand() returns a pseudo-random number:

int rand(void);

Note that some compilers accept the omission of the void keyword between the parentheses. However, it is preferable to write it systematically in order to ensure the portability of the code to another compiler.

Exercises

Exercise 1

Write a function printBase(unsigned int n, unsigned char base) which displays the integer n in the base base followed by a line feed:

The first parameter (n) is the number to display.
The second parameter (base) is the base in which n will be displayed.

The base parameter can take only three values:

8 : displays n in octal base (format code %o)
10 : displays n in decimal base
16 : displays n in hexadecimal base

We provide the beginning of the main program that asks the user to enter an integer. Complete this program so that the integer entered is displayed in the three bases:

Enter a positive integer: 185
In octal: 271
In decimal: 185
In hexadecimal: b9

Faire l'exercice

Solution

Exercise 2

Write a function input() that captures a value from the keyboard and returns the value. The body of the input() function should contain only 3 lines:

the declaration of a value variable
the keyboard entry with scanf().
the return of the note with return

Test the function with the following main program:

int main(void) {

  float n1, n2;

  // Ask the values
  printf ("Enter a value: ");
  n1 = input();
  printf ("Enter another value: ");
  n2 = input();

  // Display the average
  printf ("Average = %.2f\n", (n1+n2)/2);

  return 0;
}

Enter a value: 12.4
Enter another value: 13.7
Average = 13.05

Faire l'exercice

Solution

Quiz

Which of these functions do not receive any parameters?

void fct(int n);

void fct(void);

int fct(void);

int fct();

Check Bravo! A function without parameters contains void or nothing between the parentheses

Which of these functions do not return any parameters?

void fct(int n);

void fct(void);

int fct(void);

int fct(int n);

Check Bravo! void must precede the function name to indicate that it does not return a value.

Let's consider the following function, which statements are correct?

void update(void);

the syntax is not correct

the function is strictly useless

the function receives no parameters

the function returns no value

Check

Which functions receive no input parameters and return 2?

void fct(inta, int b);

int, int fct (void);

[int, int] fct (void)

None of the other answers