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# C Recursion

### How recursion works?

```void recurse()
{
... .. ...
recurse();
... .. ...
}

int main()
{
... .. ...
recurse();
... .. ...
}```

To prevent infinite recursion, if…else statement (or similar approach) can be used where one branch makes the recursive call, and other doesn’t.

### Example: Sum of Natural Numbers Using Recursion

``````#include <stdio.h>
int sum(int n);

int main(){
int number, result;

printf("Enter a positive integer: ");
scanf("%d", &number);

result = sum(number);

printf("sum = %d", result);
return 0;
}

int sum(int n){
if (n != 0)
// sum() function calls itself
return n + sum(n-1);
else
return n;
}
``````

Output

```Enter a positive integer:3
sum = 6```

Initially, the `sum()` is called from the `main()` function with number passed as an argument.

Suppose, the value of n inside `sum()` is 3 initially. During the next function call, 2 is passed to the `sum()` function. This process continues until n is equal to 0.

When n is equal to 0, the `if` condition fails and the `else` part is executed returning the sum of integers ultimately to the `main()` function.

Recursion makes program elegant. However, if performance is vital, use loops instead as recursion is usually much slower.

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