C Language. W3Schools in English. Lessons for beginners

Ua Es De

C Recursion


Recursion is the technique of making a function call itself. This technique provides a way to break complicated problems down into simple problems which are easier to solve.

Recursion may be a bit difficult to understand. The best way to figure out how it works is to experiment with it.

Recursion Example

Adding two numbers together is easy to do, but adding a range of numbers is more complicated. In the following example, recursion is used to add a range of numbers together by breaking it down into the simple task of adding two numbers:


int sum(int k);

int main() {
  int result = sum(10);
  printf("%d", result);
  return 0;

int sum(int k) {
  if (k > 0) {
    return k + sum(k - 1);
  } else {
    return 0;
Try it Yourself »

Example Explained

When the sum() function is called, it adds parameter k to the sum of all numbers smaller than k and returns the result. When k becomes 0, the function just returns 0. When running, the program follows these steps:

10 + sum(9)
10 + ( 9 + sum(8) )
10 + ( 9 + ( 8 + sum(7) ) )
10 + 9 + 8 + 7 + 6 + 5 + 4 + 3 + 2 + 1 + sum(0)
10 + 9 + 8 + 7 + 6 + 5 + 4 + 3 + 2 + 1 + 0

Since the function does not call itself when k is 0, the program stops there and returns the result.

The developer should be very careful with recursion as it can be quite easy to slip into writing a function which never terminates, or one that uses excess amounts of memory or processor power. However, when written correctly, recursion can be a very efficient and mathematically-elegant approach to programming.

Explanation of recursion from artificial intelligence

What is recursion?

Recursion is a programming technique that allows a program to call itself. Recursion can be used to solve complex problems that are difficult or impossible to solve using other methods.


int factorial(int n) {
   if (n == 0) {
      return 1;
   } else {
      return n * factorial(n - 1);

This program calculates the factorial of a number. The factorial of the number n is equal to the product of all integers from 1 to n.

Recursion can be used to solve many different problems.

Here are some examples:

  • Calculation of the factorial
  • Searching for elements in an array
  • Recursive descent
  • Calculation of Pi

Recursion in the C

  • Recursion in C is implemented using functions
  • A function that calls itself is called a recursive function
  • A recursive function must have a termination condition that will stop the recursion

Negative sides of recursion

  • Recursion can be difficult to understand and write
  • Recursion can lead to stack overflows


Recursion is a powerful programming technique that can be used to solve complex problems. However, recursion can be difficult to understand and to write.