#include<stdio.h>
#include<stdlib.h>
int main()
{
    double sum1 = 0; int sum2 = 0; double sum3 = 0, sum;
    for (int i = 1; i<=100; i++)
    {
        sum1 = sum1 + i;
    }
    for (int j = 1; j<=20; j++)
    {
        sum2 = sum2 + j*j;

    }
    for (int k = 1; k<=200; k++)
    {
        sum3 = sum3 + 1 / k;
    }
    printf("sum=%10.6lf", sum = sum1 + (double)sum2 + sum3);
    system("pause");
    return 0;
}

#include<stdio.h>
#include<stdlib.h>
int main()
{
    double sum1 = 0; int sum2 = 0; double sum3 = 0, sum;
    for (int i = 1; i<=100; i++)
    {
        sum1 = sum1 + i;        
    }
    for (int j = 1; j<=20; j++)
    {
        sum2 = sum2 + j*j;

    }
    for (int k = 1; k<=200; k++)
    {
        sum3 = sum3 + 1 / k;   //   1/k运算的结果是整型的，定义为double只是在整型数据后面加了几个0， 改为 sum3 = sum3 + (double) 1/k;先对它进行类型转换
    }
    printf("sum=%10.6lf", sum = sum1 + (double)sum2 + sum3);    //sum2本来就是double型，在这再次强制类型转换没有意义
    system("pause");
    return 0;
}