4、题目：函数fun的功能：返回1+12+123+1234+12345……共n≤9项相加的值。例如：输入5输出 sum=13715 #include stdiohint funint n int sum=0; int t=0i; Program End return sum;int main int n; do printf请输入n1

#include <stdio.h>

int fun(int n) { int sum = 0; int t = 0; for (int i = 1; i <= n; i++) { t = t * 10 + i; sum += t; } return sum; }

int main() { int n; do {
printf("请输入n（1~9）："); scanf("%d", &n); } while (n < 1 || n > 9); printf("sum = %d\n", fun(n)); return 0; }