Exercise 10-1 calculate the sum of 1 to n using recursive functions

practice 10-1 Use recursive functions to calculate 1 To n The sum of the (10 branch )

This problem requires the realization of a recursive calculation 1+2+3+…+n Simple function of sum of .

Function interface definition ：

int sum( int n );

This function is used for the positive integer passed in n return 1+2+3+…+n And ; if n If it is not a positive integer, return 0. The title guarantees that the input and output are in the long integer range . It is suggested to try to write recursive functions .

Sample referee test procedure ：

#include <stdio.h>

int sum( int n );

int main()
{
    int n;

    scanf("%d", &n);
    printf ("%d\n", sum(n));

    return 0;
}

/*  Your code will be embedded here  */

sample input 1：

10

sample output 1：

55

sample input 2：

0

sample output 2：

0

int sum( int n ){
    int s;
    if(n<=0){
        s=0;
    }else{
        s=n+sum(n-1);
    }
    return s;
}