程序代码：

# include<stdio.h>

int main(void)
{
    int i;
    int sum = 0;

    for (i=1; i<=4; ++i)//1+2+3+4=10  ++i呢？？？？？不懂详细解释
       
        sum = sum + i;//不懂

    printf("sum = %d\n",sum);

    return 0;
}