What is the rules of recursion?

Question

Write a recursive function:

int sum( int x, int max ) 
{ 
  /* complete the code */ 
} 

that calculates the sum of the numbers from x to max (inclusive). For example, sum (4, 7) would compute 4 + 5 + 6 + 7 and return the value 22.

Note: The function must be recursive.

Answer 1

There are two points which you have to remember while writing a recursion program.

1.The basic i.e a function calling itself (its called recursion)

int recursion(int number)
{
    printf("My number is: %d\n", number);
    return recursion(--number); 
}
int main()
{
    recursion(10);
    return 0;
}

2.There should be a break point, when your program should stop its execution else it will crash due to stack over flow.

int recursion(int number)
{
    printf("My number is: %d\n", number);

    if (number == 0) {   // it will stop the calling itself when number reaches to zero.
        return 0;
    }   
    return recursion(--number);
}

int main()
{
    recursion(10);
    return 0;
}

Note:
# In 1st point the program will definitely crash [because there is no check which stop the calling of the function recursion()]
# In 2nd point the program will print 10 to 0 and then stop, the output will be

 My number is: 10
 My number is: 9
 My number is: 8
 My number is: 7
 My number is: 6
 My number is: 5
 My number is: 4
 My number is: 3
 My number is: 2
 My number is: 1
 My number is: 0

I think with the above example I have given your answer.