求大神讲解一下答案是怎么得出来的? 谢谢!

Question

#include"stdio.h"#include"string.h"#include"conio.h"#include"windows.h"#include"math.h"int f ( int );int sum ( int );int main(){ int a,b; printf("输入一个整数:");scanf("%d",&a); b = sum ( a ); printf(" a = %d \t b = %d \n",a,b); return 0;}int sum ( int n ){ int x; int s = 0; for ( x = 0; x <= n; x ++ ) {  s += f ( x ); } return s;}int f ( int z ){ return z*z+1;}请讲解一下答案是怎么算出来的?

Answer 1

一个循环啊，不断地调用函数f。