参考方法：

#include<stdio.h>
#include<math.h>

int main()
{
    int i, a, n, sum=0;
    printf("请输入 a 和 n：\n");
    scanf("%d%d", &a, &n);
    for(i=0; i<n; i++)
    {
        sum += a*pow(10, i)*(n-i);
    }
    printf("sum is %d\n", sum);
    return 0;
}

参考方法：

#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
//给数组分配动态内存
int *get_number(int all){
    int *temp_number = NULL;
    //分配空间
    temp_number = (int *)malloc((all + 1) * sizeof(int));
    if (temp_number == NULL)
    {
        fprintf(stderr, "temp_number malloc err\n");
        return NULL;
    }
    //初始化
    memset(temp_number, 0, (all + 1) * sizeof(int));
    return temp_number;
}

//释放分配空间
void free_number(int *number){
    if (number == NULL)
    {
        return;
    }
    free(number);
    number = NULL;
    return;
}
int main(void){
    int all = 0, num = 0;
    int count = 0;
    int s = 0;
    int *number = NULL;
    printf("几个数相加？什么数？\n");
    scanf("%d %d", &all, &num);
    number = get_number(all);

    for (count = 0; count < all; count++)
    {
        number[count] += num;
        s += number[count];
        number[count + 1] = number[count] * 10;
    }
    number[all] = '\0';
    
    for (count = 0; count < (all - 1); count++)
    {
        printf("%d + ", number[count]);
    }
    printf("%d = %d\n", number[count], s);
    free_number(number);
    return 0;
}

参考方法：

#include <stdio.h>

int main(){
    int sum=0,a,n,temp;
    while(scanf("%d%d",&a,&n)!=EOF){
        temp=a;
        while(n--){
            sum+=temp;
            temp=temp*10+a;
        }
        printf("sum=%d\n",sum);
    }

    return 0;
}