Recursion- sum of n natural number

Question

function to calculate the sum of n natural number

int solve(int n)
{
    if(n==0 or n==1)
    return n;
    int sum=0;

    sum=sum+n;
    solve(n-1);   // gives me wrong output

    return sum;
}

int solve(int n)
{
    if(n==0 or n==1)
    return n;
    int sum=0;

    sum=sum+solve(n-1);  // gives me correct output

    return sum;
}

what is the difference in the working or output of both the function as call stack works same in both the cases

Answer 1

solve function in the first method does not have any effect in your program

int solve(int n)
{
    if(n==0 or n==1)
    return n;
    int sum=0;

    sum=sum+n;
    solve(n-1);   // has not any effect

    return sum;
}

In the second method, returned value will always be 1 while it must return the sum of the numbers, correct code for calculate sum of numbers is:

int solve(int n)
{
    if (n == 0 || n == 1)
        return n;

    int sum = 0;

    sum = n + solve(n - 1);  // change 'sum' with 'n'

    return sum;
}

Run:

solve(5);

Output:

5 + 4 + 3 + 2 + 1 = 15