K&R的名著:<C程序设计语言>小程序总结5

1、readlines函数：读取输入行
int readlines(char *lineptr[], int maxlines)
{
      int len, nlines;
      char *p, line[MAXLEN];
      nlines = 0;
      while ((len = getline(line, MAXLINE)) > 0)
         if (nlines >= maxlines || (p = alloc(len)) == NULL)
                return -1;
         else  {
              line[len-1] = '\0';
             strcpy(p, line);
             lineptr[nlines++] = p;
 }
  return nlines;
           
}
2、writelines函数：写输出行
void writelines(char *lineptr[], int nlines)
{
    int i;
    for (i = 0; i < nlines; i++)
       printf("%s\n", lineptr[i]);
}
 
3、二维数组的运用
a、day_of_year函数：将某月某日的日期表示形式转换为某一年中的第几天
int day_of_year(int year, int month, int day)
{
        int i, leap;
        //int *ptr;
        leap = year%4 ==0 && year%100 !=0 || year % 400 ==0;
        for (i = 1; i < month; i++)
               day +=daytab[leap][i];
        return day;
}
b、month_day函数：与上述功能相反
void month_day(int year, int yearday, int *pmonth, int *pday)
{
     int i, leap;
     leap = year%4 ==0 && year%100 !=0 || year % 400 ==0;
     for (i = 1;yearday > daytab[leap][i]; i++)
     yearday -= daytab[leap][i];
     *pmonth = i;
     *pday = yearday;
}

#include<stdio.h>
static char daytab[2][13]={
{0,31,28,31,30,31,30,31,31,30,31,30,31},
{0,31,29,31,30,31,30,31,31,30,31,30,31}
};
void month_day(int year, int yearday, int *pmonth, int *pday)
{
int i, leap;
leap = year%4 ==0 && year%100 !=0 || year % 400 ==0;

for (i = 1;yearday > daytab[leap][i]; i++)
yearday -= daytab[leap][i];
*pmonth = i;
*pday = yearday;
}

void main(void)
{
int mon,day;
int year,yearday;

printf("please input year:");
scanf("%d",&year);
printf("please input yearday:");
scanf("%d",&yearday);
month_day(year,yearday,&mon,&day);

printf("it is %d month %d day\n",mon,day);
}

 
c、指针数组的初始化
char *month_name(int n)
{
   static char *name[]={
    "Illegal month",
    "Jan", "Feb", "Mar",
    "Apr", "May","June",
    "July", "Aug", "Sep",
    "Nov", "Dem"
};
return (n < 1 || n > 12)?name[0] : name
;
}

#include "stdio.h"

char *month_name(int n){
static char *name[]={
"Illegal month",
"Jan", "Feb", "Mar",
"Apr", "May","June",
"July", "Aug", "Sep",
"Nov", "Dem"};
return (n<1||n>12)?name[0]:name
;
}

void main(void){
int n;
printf("Please the month:");
scanf("%d",&n);
printf("the month is %s\n",month_name(n));
}

 
 
4、模式查找程序，类似Linux平台的grep命令作用
//p100.c
#include<stdio.h>
#include<string.h>
 
#define MAXLINE 1000
 
int getline1(char *line, int max);//因getline函数在linux平台已有定义且与此函数的参数不同，所以改名为getline1()
 
int main(int argc, char *argv[])
{
        char line[MAXLINE];
        int found = 0;
 
        if (argc != 2)
               printf("Usage: find pattern\n");
        else
               while (getline1(line, MAXLINE) > 0)
                       if (strstr(line ,argv[1]) != NULL) {
                       printf("%s",line);
                       found++;
                       }
        return found;
 
}
 
int getline1(char *s, int lim)
{
   int c;
   char *t = s;
 
   while(--lim > 0 && (c =getchar()) !=EOF && c != '\n')
           *s++ = c;
   if (c == '\n')
           *s++ = c;
   *s ='\0';
   return s-t;
 
}