#include <stdio.h>int main(void)
{
   int result;
   char buffer[512];   printf("Testing to see if drive a: is ready\n");
   result = biosdisk(4,0,0,0,0,1,buffer);
   result &= 0x02;
   (result) ? (printf("Drive A: Ready\n")) :
	    (printf("Drive A: Not Ready\n"));   return 0;
}
函數名: bioskey
功  能: 直接使用BIOS服務的鍵盤接口
用  法: int bioskey(int cmd);
程序例:#include <stdio.h>
#include <bios.h>
#include <ctype.h>#define RIGHT  0x01
#define LEFT   0x02
#define CTRL   0x04
#define ALT    0x08int main(void)
{
   int key, modifiers;   /* function 1 returns 0 until a key is pressed */
   while (bioskey(1) == 0);   /* function 0 returns the key that is waiting */
   key = bioskey(0);   /* use function 2 to determine if shift keys were used */
   modifiers = bioskey(2);   if (modifiers)
   {
      printf("[");
      if (modifiers & RIGHT) printf("RIGHT");
      if (modifiers & LEFT)  printf("LEFT");
      if (modifiers & CTRL)  printf("CTRL");
      if (modifiers & ALT)   printf("ALT");
      printf("]");
   }
   /* print out the character read */
   if (isalnum(key & 0xFF))
      printf("'%c'\n", key);
   else      printf("%#02x\n", key);
   return 0;
}
函數名: biosmemory
功  能: 返回存儲塊大小
用  法:int biosmemory(void);
程序例:
#include <stdio.h>
#include <bios.h>
int main(void)
{
   int memory_size;
   memory_size = biosmemory();
		  /* returns value up to 640K */
   printf("RAM size = %dK\n",memory_size);
   return 0;
}
函數名: biosprint
功  能: 直接使用BIOS服務的打印機I/O
用  法: int biosprint(int cmd, int byte, int port);
程序例:
#include <stdio.h>
#include <conio.h>
#include <bios.h>int main(void)
{
   #define STATUS  2    /* printer status command */
   #define PORTNUM 0    /* port number for LPT1 */   int status, abyte=0;   printf("Please turn off your printer.\
	   Press any key to continue\n");
   getch();
   status = biosprint(STATUS, abyte, PORTNUM);
   if (status & 0x01)
      printf("Device time out.\n");
   if (status & 0x08)
      printf("I/O error.\n");   if (status & 0x10)
      printf("Selected.\n");
   if (status & 0x20)
      printf("Out of paper.\n");   if (status & 0x40)
      printf("Acknowledge.\n");
   if (status & 0x80)
      printf("Not busy.\n");   return 0;
}
函數名: biostime
功  能: 讀取或設置BIOS時間
用  法: long biostime(int cmd, long newtime);
程序例:#include <stdio.h>
#include <bios.h>
#include <time.h>
#include <conio.h>int main(void)
{
   long bios_time;
   clrscr();   cprintf("The number of clock ticks since midnight\
	    is:\r\n");
   cprintf("The number of seconds since midnight is:\r\n");
   cprintf("The number of minutes since midnight is:\r\n");
   cprintf("The number of hours since midnight is:\r\n");
   cprintf("\r\nPress any key to quit:");
   while(!kbhit())
   {
      bios_time = biostime(0, 0L);      gotoxy(50, 1);
      cprintf("%lu", bios_time);      gotoxy(50, 2);
      cprintf("%.4f", bios_time / CLK_TCK);      gotoxy(50, 3);
      cprintf("%.4f", bios_time / CLK_TCK / 60);      gotoxy(50, 4);
      cprintf("%.4f", bios_time / CLK_TCK / 3600);
   }
   return 0;
}
函數名: brk
功  能: 改變數據段空間分配
用  法: int brk(void *endds);
程序例:#include <stdio.h>
#include <alloc.h>int main(void)
{
   char *ptr;   printf("Changing allocation with brk()\n");
   ptr = malloc(1);   printf("Before brk() call:%lu bytes free\n",coreleft());
   brk(ptr+1000);
   printf(" After brk() call:%lu bytes free\n",coreleft());
   return 0;
}
函數名: bsearch
功  能: 二分法搜索
用  法: void *bsearch( const void *key, const void *base,
		       size_t *nelem, size_t width,
		       int(*fcmp)(const void *, const *));
程序例:
#include <stdlib.h>
#include <stdio.h>
#define NELEMS(arr) (sizeof(arr) / sizeof(arr[0]))
int numarray[] = {123, 145, 512, 627, 800, 933};
int numeric (const int *p1, const int *p2)
{
   return(*p1 - *p2);
}int lookup(int key)
{
   int *itemptr;   /* The cast of (int(*)(const void *,const void*))
      is needed to avoid a type mismatch error at
      compile time */
   itemptr = bsearch (&key, numarray, NELEMS(numarray),
   sizeof(int), (int(*)(const void *,const void *))numeric);
   return (itemptr != NULL);
}int main(void)
{
   if (lookup(512))
      printf("512 is in the table.\n");
   else
      printf("512 isn't in the table.\n");   return 0;
}字母Ｃ開頭函數
函數名: cabs
功  能: 計算復數的絕對值
用  法: double cabs(struct complex z);
程序例:
#include <stdio.h>
#include <math.h>
int main(void)
{
   struct complex z;
   double val;
   z.x = 2.0;
   z.y = 1.0;
   val = cabs(z);   printf("The absolute value of %.2lfi %.2lfj is %.2lf\
	   ", z.x, z.y, val);
   return 0;
}
函數名: calloc
功  能: 分配主存儲器
用  法: void *calloc(size_t nelem, size_t elsize);
程序例:#include <stdio.h>
#include <alloc.h>int main(void)
{
   char *str = NULL;
   /* allocate memory for string */
   str = calloc(10, sizeof(char));
   /* copy "Hello" into string */   strcpy(str, "Hello");
   /* display string */
   printf("String is %s\n", str);
   /* free memory */
   free(str);
   return 0;
}
函數名: ceil
功  能: 向上舍入
用  法: double ceil(double x);
程序例:#include <math.h>
#include <stdio.h>int main(void)
{
   double number = 123.54;
   double down, up;   down = floor(number);   up = ceil(number);   printf("original number     %5.2lf\n", number);
   printf("number rounded down %5.2lf\n", down);
   printf("number rounded up   %5.2lf\n", up);   return 0;
}
函數名: cgets
功  能: 從控制臺讀字符串
用  法: char *cgets(char *str);
程序例:#include <stdio.h>
#include <conio.h>int main(void)
{
   char buffer[83];
   char *p;
   /* There's space for 80 characters plus the NULL \
      terminator */   buffer[0] = 81;   printf("Input some chars:");
   p = cgets(buffer);
   printf("\ncgets read %d characters: \"%s\"\n\
	  ", buffer[1], p);
   printf("The returned pointer is %p, buffer[0] is at %p\n\
	  ", p, &buffer);
   /* Leave room for 5 characters plus the NULL terminator */
   buffer[0] = 6;   printf("Input some chars:");
   p = cgets(buffer);
   printf("\ncgets read %d characters: \"%s\"\n\
	  ", buffer[1], p);   printf("The returned pointer is %p, buffer[0] is at %p\n\
	  ", p, &buffer);
   return 0;
}
函數名: chdir
功  能: 改變工作目錄
用  法: int chdir(const char *path);
程序例:#include <stdio.h>
#include <stdlib.h>
#include <dir.h>char old_dir[MAXDIR];
char new_dir[MAXDIR];int main(void)
{
   if (getcurdir(0, old_dir))
   {  perror("getcurdir()");
      exit(1);
   }
   printf("Current directory is: \\%s\n", old_dir);
   if (chdir("\\"))
   {  perror("chdir()");
      exit(1);
   }
   if (getcurdir(0, new_dir))
   {  perror("getcurdir()");
      exit(1);
   }   printf("Current directory is now: \\%s\n", new_dir);   printf("\nChanging back to orignal directory: \\%s\n\
	  ", old_dir);
   if (chdir(old_dir))
   {  perror("chdir()");
      exit(1);
   }
   return 0;
}
函數名: _chmod, chmod
功  能: 改變文件的訪問方式
用  法: int chmod(const char *filename, int permiss);
程序例:#include <sys\stat.h>
#include <stdio.h>
#include <io.h>void make_read_only(char *filename);int main(void)
{  make_read_only("NOTEXIST.FIL");
   make_read_only("MYFILE.FIL");   return 0;
}void make_read_only(char *filename)
{  int stat;
   stat = chmod(filename, S_IREAD);
   if (stat)
      printf("Couldn't make %s read-only\n", filename);
   else
      printf("Made %s read-only\n", filename);
}
函數名: chsize
功  能: 改變文件大小
用  法: int chsize(int handle, long size);
程序例:#include <string.h>
#include <fcntl.h>
#include <io.h>int main(void)
{
   int handle;
   char buf[11] = "0123456789";
   /* create text file containing 10 bytes */
   handle = open("DUMMY.FIL", O_CREAT);
   write(handle, buf, strlen(buf));   /* truncate the file to 5 bytes in size */
   chsize(handle, 5);   /* close the file */
   close(handle);
   return 0;}
函數名: circle
功  能: 在給定半徑以(x, y)為圓心畫圓
用  法: void far circle(int x, int y, int radius);
程序例:#include <graphics.h>
#include <stdlib.h>
#include <stdio.h>
#include <conio.h>int main(void)
{
   /* request auto detection */
   int gdriver = DETECT, gmode, errorcode;   int midx, midy;
   int radius = 100;   /* initialize graphics and local variables */
   initgraph(&gdriver, &gmode, "");   /* read result of initialization */
   errorcode = graphresult();   if (errorcode != grOk)  /* an error occurred */
   {
      printf("Graphics error: %s\n\
	     ", grapherrormsg(errorcode));
      printf("Press any key to halt:");      getch();
      exit(1); /* terminate with an error code */
   }
   midx = getmaxx() / 2;
   midy = getmaxy() / 2;
   setcolor(getmaxcolor());   /* draw the circle */
   circle(midx, midy, radius);   /* clean up */
   getch();
   closegraph();
   return 0;
}
函數名: cleardevice
功  能: 清除圖形屏幕
用  法: void far cleardevice(void);
程序例:#include <graphics.h>
#include <stdlib.h>
#include <stdio.h>
#include <conio.h>int main(void)
{
   /* request auto detection */
   int gdriver = DETECT, gmode, errorcode;   int midx, midy;   /* initialize graphics and local variables */
   initgraph(&gdriver, &gmode, "");   /* read result of initialization */
   errorcode = graphresult();   if (errorcode != grOk)  /* an error occurred */
   {
      printf("Graphics error: %s\n\
	     ", grapherrormsg(errorcode));
      printf("Press any key to halt:");
      getch();      exit(1); /* terminate with an error code */
   }
   midx = getmaxx() / 2;
   midy = getmaxy() / 2;
   setcolor(getmaxcolor());   /* for centering screen messages */
   settextjustify(CENTER_TEXT, CENTER_TEXT);   /* output a message to the screen */
   outtextxy(midx,midy,"press any key to clear the screen:");   /* wait for a key */
   getch();   /* clear the screen */
   cleardevice();   /* output another message */
   outtextxy(midx, midy, "press any key to quit:");   /* clean up */
   getch();
   closegraph();
   return 0;
}
函數名: clearerr
功  能: 復位錯誤標志
用  法:void clearerr(FILE *stream);
程序例:#include <stdio.h>int main(void)
{
   FILE *fp;
   char ch;   /* open a file for writing */
   fp = fopen("DUMMY.FIL", "w");   /* force an error condition by attempting to read */
   ch = fgetc(fp);
   printf("%c\n",ch);   if (ferror(fp))
   {
      /* display an error message */
      printf("Error reading from DUMMY.FIL\n");      /* reset the error and EOF indicators */
      clearerr(fp);
   }   fclose(fp);
   return 0;
}
函數名: clearviewport
功  能: 清除圖形視區
用  法: void far clearviewport(void);
程序例:#include <graphics.h>
#include <stdlib.h>
#include <stdio.h>
#include <conio.h>#define CLIP_ON 1   /* activates clipping in viewport */int main(void)
{   /* request auto detection */
   int gdriver = DETECT, gmode, errorcode;
   int ht;   /* initialize graphics and local variables */
   initgraph(&gdriver, &gmode, "");   /* read result of initialization */
   errorcode = graphresult();   if (errorcode != grOk)  /* an error occurred */
   {
      printf("Graphics error: %s\n\
	     ", grapherrormsg(errorcode));      printf("Press any key to halt:");
      getch();
      exit(1); /* terminate with an error code */
   }   setcolor(getmaxcolor());
   ht = textheight("W");   /* message in default full-screen viewport */
   outtextxy(0, 0, "* <-- (0, 0) in default viewport");   /* create a smaller viewport */
   setviewport(50, 50, getmaxx()-50, getmaxy()-50, CLIP_ON);
   /* display some messages */
   outtextxy(0, 0, "* <-- (0, 0) in smaller viewport");
   outtextxy(0, 2*ht, "Press any key to clear viewport:");   /* wait for a key */
   getch();   /* clear the viewport */
   clearviewport();   /* output another message */
   outtextxy(0, 0, "Press any key to quit:");   /* clean up */   getch();
   closegraph();
   return 0;
}
函數名: _close, close
功  能: 關閉文件句柄
用  法: int close(int handle);
程序例:#include <string.h>
#include <stdio.h>
#include <fcntl.h>
#include <io.h>main()
{
   int handle;
   char buf[11] = "0123456789";   /* create a file containing 10 bytes */
   handle = open("NEW.FIL", O_CREAT);
   if (handle > -1)
   {
       write(handle, buf, strlen(buf));       /* close the file */
       close(handle);
   }
   else
   {
       printf("Error opening file\n");
   }   return 0;
}
函數名: clock
功  能: 確定處理器時間
用  法: clock_t clock(void);
程序例:#include <time.h>
#include <stdio.h>
#include <dos.h>int main(void)
{
   clock_t start, end;
   start = clock();
   delay(2000);   end = clock();
   printf("The time was: %f\n", (end - start) / CLK_TCK);   return 0;
}
函數名: closegraph
功  能: 關閉圖形系統
用  法: void far closegraph(void);
程序例:#include <graphics.h>
#include <stdlib.h>
#include <stdio.h>
#include <conio.h>int main(void)
{
   /* request auto detection */
   int gdriver = DETECT, gmode, errorcode;   int x, y;   /* initialize graphics mode */
   initgraph(&gdriver, &gmode, "");   /* read result of initialization */
   errorcode = graphresult();   if (errorcode != grOk)  /* an error
      occurred */
   {
      printf("Graphics error: %s\n\
	     ", grapherrormsg(errorcode));      printf("Press any key to halt:");
      getch();
      exit(1); /* terminate with an error code */
   }
   x = getmaxx() / 2;
   y = getmaxy() / 2;   /* output a message */
   settextjustify(CENTER_TEXT, CENTER_TEXT);