Void, Recursion

The void Return Type in C

In the C programming language, functions that are declared with a specific return type are expected to have a return statement, delivering a value matching that type. However, there are scenarios where a function doesn't need to return anything – perhaps it's simply displaying text on the screen. For such instances, the function should be declared with the void type.

Main


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#include <stdio.h>

void func()
{
    printf("This function returns nothing\n");
}

int main()
{
    func();

    return 0;
}

The void keyword specifies that a function doesn't return a value, and it can also be used in the context of pointers. Attempting to declare a variable of type void will result in an error because the compiler won't understand how much memory to allocate.

Here's an intentional error for illustration.

Main


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#include <stdio.h>

int main()
{
    void variable;

    return 0;
}

Delving into Recursion

C supports the ability for a function to call itself, a technique known as recursion.

Imagine recursion as the action of stretching and then releasing a rubber band. It's commonly leveraged in mathematical operations, such as calculating factorials.

For instance: 3! = 3 x 2 x 1

Factorials are often utilized in approximating function values by expanding these functions into Taylor or Maclaurin series.

Note
This chapter's inspiration came right after the author completed a lab assignment at a university. The task was to approximate the cotangent value to a certain precision by expanding it into a Taylor series. And naturally, the factorial computation was indispensable.

Main


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#include <stdio.h>

int factorial(int n) 
{
    // if n = 0 or 1, because 0! = 1 and 1! = 1
    if (n == 0 || n == 1)
        return 1;
    // recursion case
    else
        return n * factorial(n - 1);
}

int main()
{
    int n = 3;

    printf("factorial(%d) = %d\n", n, factorial(n));

    return 0;
}

In the context of recursion, the function will continue to call itself until it meets the condition n == 0 || n == 1. Once this condition is satisfied, the results from the subsequent factorial() function calls are returned in the reverse order, similar to folding an accordion. By the time step 6 is reached, the initial call to factorial(3) will return 6.

Everything was clear?

Section 5. Chapter 6