这是代码
#include <stdio.h>

int leap(int year )
{
 return ((year %4 == 0) && (year % 100 != 0)
  || (year % 400 == 0));
}

void show(int year,int month)
{
 const char month_str[][4]={ "Jan","Feb","Mar","Apl",
  "May","Jun","Jul","Aug","Sep","Oct","Nov","Dec"};
 const int month_day[]={0,31,28,31,30,31,30,31,31,30,31,30,31};
 int i;
 int j;
 int wdays;
 int mdays;
 int days;
 int m;

 while(i<year)
 { i=1;
 days=0;
  if(leap(i))
  {
   days += 366;
  }
  else
  {
   days += 365;
  }
  i++;
 }
 while (i<month)
 {i=1;
  if(i==2 && leap(year))
  {
   days+=29;
  }
  else
  {
   days+=month_day[i];
  }
 i++;
 }

 printf(" %s (%d)\n",month_str[month-1],year);
 printf(" Mon Tue Wed Thu Fri Sat Sun\n");
 m=days/7-(int)days/7;
 wdays=7*m ;
 while(j<wdays)
 { j=0;
  printf("%4c",' ');
j++;
 }
 if(month == 2 && leap(year))
 {
  mdays=29;
 }
 else
 {
  mdays= month_day[month];
 }
while(i<=mdays)
 { i=1;
  if( i > 1 && days % 7 == 0  )
  {
   printf("\n");
  }
  printf("%4d",i);
  i++;
  days=days+1;
 }
 printf("\n---------------------------\n");
}
 main()
{
int year,month;

printf("输入年和月份:");
scanf("%d%d",&year,&month);
show(year,month);
 }

main()
{
int year;
int month;
printf("输入年和月份:");
scanf("%d%d",&year,&month);
show(year,month);
}

while(i<year)
 你的i 根本没有初始化，比较有意义吗

那i初始化等于1应该放在什么地方呢

int i;
 就放到定义出啊，
int i=1;

还有下次写程序把注释加上，不然我们改错会很困难

给各位添麻烦了。i和j都改了，运行还是不对，要求是输出万年历，结果没有出现下面的数字

我在你的基础上改了一下，没全改完，不好意思，偶先睡觉去了~~
对啦，记得要写注释，不然我们帮忙找问题会很辛苦的~~
#include <stdio.h>

int leap(int year )
{
return ((year %4 == 0) && (year % 100 != 0) || (year % 400 == 0));
}

void show(int year,int month)
{
const char month_str[][4]={ "Jan","Feb","Mar","Apl",
  "May","Jun","Jul","Aug","Sep","Oct","Nov","Dec"};
const int month_day[]={31,28,31,30,31,30,31,31,30,31,30,31}; /*怎么前面有个0？*/
int i;
int j;
int wdays;
int mdays;
int days;
int m;

i=0;
while(i<year)                         /*i没初始化怎么比较？*/
{ i=1;
days=0;
  if(leap(i))
  {
   days += 366;
  }
  else
  {
   days += 365;
  }
  i++;
}
i=0;
while (i<month)                  /*上面用过i了，i应该重新初始化*/
{i=1;
  if(i==2 && leap(year))
  {
   days+=29;
  }
  else
  {
   days+=month_day[i-1];            /*注意数组是以0开始，我知道你前面为什么多个0了，这样才是好的方法*/
  }
i++;
}

printf(" %s (%d)\n",month_str[month-1],year);
printf(" Mon Tue Wed Thu Fri Sat Sun\n");
m=days/7-(int)(days/7);                     /*这里有问题m，days都是整型怎么算m都是0*/
wdays=7*m ;
while(j<wdays)              /*后面这一小节自己研究看看有没问题吧，偶睡觉去咯~~*/
{ j=0;
  printf("%4c",' ');
j++;
}
if(month == 2 && leap(year))
{
  mdays=29;
}
else
{
  mdays= month_day[month];
}
while(i<=mdays)
{ i=1;
  if( i > 1 && days % 7 == 0  )
  {
   printf("\n");
  }
  printf("%4d",i);
  i++;
  days=days+1;
}
printf("\n---------------------------\n");
}
                                      /*多了个main函数*/

main()
{
int year;
int month;
printf("输入年和月份:");
scanf("%d%d",&year,&month);
show(year,month);
return 0;
}

麻烦再看看下面有没有错误吧
while(j<wdays)                /*wdays是1年到所在月1号的所有天数和7的余数，让输出的万年历1号之前的天数都变成空格*/
 { j=0;
  printf("%4c",' ');
j++;
 }
 if(month == 2 && leap(year))           /*mdays是所在月的天数*/
 {
  mdays=29;
 }
 else
 {
  mdays= month_day[month];
 }
while(i<=mdays)
 { i=1;
  if( i > 1 && days % 7 == 0  )              /*当1年到所在天总的天数被7整除时万年历换行，好了，就这样了*/

  {
   printf("\n");
  }
  printf("%4d",i);
  i++;
  days=days+1;
 }
 printf("\n---------------------------\n");
}
 main()
{
int year,month;

printf("输入年和月份:");
scanf("%d%d",&year,&month);
show(year,month);
 }

main()
{
int year;
int month;
printf("输入年和月份:");
scanf("%d%d",&year,&month);
show(year,month);
}