#include <stdio.h>
#define MONTHS 12
#define YEARS 5
int main(void)
{
    const int rain[YEARS][MONTHS]=
    {
 {4.3,4.3,4.3,3.0,2.0,1.2,0.2,0.2,0.4,2.4,3.5,6.6},
 {8.5,8.2,1.2,1.6,2.4,0.0,5.2,0.9,0.3,0.9,1.4,7.3},
 {9.1,8.5,6.7,4.3,2.1,0.8,0.2,0.2,1.1,2.3,6.1,8.4},
 {7.2,9.9,8.4,3.3,1.2,0.8,0.4,0.0,0.6,1.7,4.3,6.2},
 {7.6,5.6,3.8,2.8,3.8,0.2,0.0,0.0,0.0,1.3,2.6,5.2}
 };

    int year,month;
    float subtot,total;
    printf("YEAE     RAINFALL   (inches)\n");
    for(year=0,total=0;year<YEARS;year++)
    {
        for(month=0,subtot=0;month<MONTHS;month++)
        subtot+=rain[year][month];
        printf("%5d %15.1f\n",2010+year,subtot);
        total+=subtot;
    }
    printf("\nThe year average is %.1f inches.\n\n",total/YEARS);
    printf("MONTHLY AVERAGES:\n\n");
    printf("JAN  FEB  MAR  APR  MAY  JAN  JUL  AUG  SEP  OCT  NOV  DEC\n");
    for(month=0;month<MONTHS;month++)
    {
        for(year=0,subtot=0;year<YEARS;year++)
        subtot+=rain[year][month];
        printf("%4.1f ",subtot/YEARS);
    }
    printf("\n");
    return 0;
}

二维数组里的数据是从2010年到2014年这5年中每个月的降水量，然后就是先计算一下每年的平均降水量，再计算一下从1月到12月每个月的降水量，但是程序运行结果和手动计算的结果不一样。

一语惊醒梦中人，找半天没找出来原因!THX!