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c语言的用法

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  语言程序设计是一门基础的程序设计语言,学好这门课对以后程序开发至关重要。由于C语言灵活、强大,初学者要全面地掌握它非常吃力,因此在学习C语言的过程中,但一定要熟练掌握C语言的流程控制语句、数组、函数、指针等基础知识的应用,为学习面向对象程序设计打下坚实的基础。下面小编就为大家来介绍下c语言的用法。
  c语言的用法: abort
  功 能: 异常终止一个进程
  用 法: void abort(void);
  程序例:
  #include <stdio.h>
  #include <stdlib.h>
  int main(void)
  {
  printf("Calling abort()\n");
  abort();
  return 0; /* This is never reached */
  }
  c语言的用法: abs
  功 能: 求整数的绝对值
  用 法: int abs(int i);
  程序例:
  #include <stdio.h>
  #include <math.h>
  int main(void)
  {
  int number = -1234;
  printf("number: %d absolute value: %d\n", number, abs(number));
  return 0;
  }
  c语言的用法: absread, abswirte
  功 能: 绝对磁盘扇区读、写数据
  用 法: int absread(int drive, int nsects, int sectno, void *buffer);
  int abswrite(int drive, int nsects, in tsectno, void *buffer);
  程序例:
  /* absread example */
  #include <stdio.h>
  #include <conio.h>
  #include <process.h>
  #include <dos.h>
  int main(void)
  {
  int i, strt, ch_out, sector;
  char buf[512];
  printf("Insert a diskette into drive A and press any key\n");
  getch();
  sector = 0;
  if (absread(0, 1, sector, &buf) != 0)
  {
  perror("Disk problem");
  exit(1);
  }
  printf("Read OK\n");
  strt = 3;
  for (i=0; i<80; i++)
  {
  ch_out = buf[strt+i];
  putchar(ch_out);
  }
  printf("\n");
  return(0);
  }
  c语言的用法: access
  功 能: 确定文件的访问权限
  用 法: int access(const char *filename, int amode);
  程序例:
  #include <stdio.h>
  #include <io.h>
  int file_exists(char *filename);
  int main(void)
  {
  printf("Does NOTEXIST.FIL exist: %s\n",
  file_exists("NOTEXISTS.FIL") ? "YES" : "NO");
  return 0;
  }
  int file_exists(char *filename)
  {
  return (access(filename, 0) == 0);
  }
  c语言的用法: acos
  功 能: 反余弦c语言的用法
  用 法: double acos(double x);
  程序例:
  #include <stdio.h>
  #include <math.h>
  int main(void)
  {
  double result;
  double x = 0.5;
  result = acos(x);
  printf("The arc cosine of %lf is %lf\n", x, result);
  return 0;
  }
  c语言的用法: allocmem
  功 能: 分配DOS存储段
  用 法: int allocmem(unsigned size, unsigned *seg);
  程序例:
  #include <dos.h>
  #include <alloc.h>
  #include <stdio.h>
  int main(void)
  {
  unsigned int size, segp;
  int stat;
  size = 64; /* (64 x 16) = 1024 bytes */
  stat = allocmem(size, &segp);
  if (stat == -1)
  printf("Allocated memory at segment: %x\n", segp);
  else
  printf("Failed: maximum number of paragraphs available is %u\n",
  stat);
  return 0;
  }
  c语言的用法: arc
  功 能: 画一弧线
  用 法: void far arc(int x, int y, int stangle, int endangle, 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 stangle = 45, endangle = 135;
  int radius = 100;
  /* initialize graphics and local variables */
  initgraph(&gdriver, &gmode, "");
  /* read result of initialization */
  errorcode = graphresult(); /* an error occurred */
  if (errorcode != grOk)
  {
  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 arc */
  arc(midx, midy, stangle, endangle, radius);
  /* clean up */
  getch();
  closegraph();
  return 0;
  }
  c语言的用法: asctime
  功 能: 转换日期和时间为ASCII码
  用 法: char *asctime(const struct tm *tblock);
  程序例:
  #include <stdio.h>
  #include <string.h>
  #include <time.h>
  int main(void)
  {
  struct tm t;
  char str[80];
  /* sample loading of tm structure */
  t.tm_sec = 1; /* Seconds */
  t.tm_min = 30; /* Minutes */
  t.tm_hour = 9; /* Hour */
  t.tm_mday = 22; /* Day of the Month */
  t.tm_mon = 11; /* Month */
  t.tm_year = 56; /* Year - does not include century */
  t.tm_wday = 4; /* Day of the week */
  t.tm_yday = 0; /* Does not show in asctime */
  t.tm_isdst = 0; /* Is Daylight SavTime; does not show in asctime */
  /* converts structure to null terminated
  string */
  strcpy(str, asctime(&t));
  printf("%s\n", str);
  return 0;
  }
  c语言的用法: asin
  功 能: 反正弦c语言的用法
  用 法: double asin(double x);
  程序例:
  #include <stdio.h>
  #include <math.h>
  int main(void)
  {
  double result;
  double x = 0.5;
  result = asin(x);
  printf("The arc sin of %lf is %lf\n", x, result);
  return(0);
  }
  c语言的用法: assert
  功 能: 测试一个条件并可能使程序终止
  用 法: void assert(int test);
  程序例:
  #include <assert.h>
  #include <stdio.h>
  #include <stdlib.h>
  struct ITEM {
  int key;
  int value;
  };
  /* add item to list, make sure list is not null */
  void additem(struct ITEM *itemptr) {
  assert(itemptr != NULL);
  /* add item to list */
  }
  int main(void)
  {
  additem(NULL);
  return 0;
  }
  c语言的用法: atan
  功 能: 反正切c语言的用法
  用 法: double atan(double x);
  程序例:
  #include <stdio.h>
  #include <math.h>
  int main(void)
  {
  double result;
  double x = 0.5;
  result = atan(x);
  printf("The arc tangent of %lf is %lf\n", x, result);
  return(0);
  }
  c语言的用法: atan2
  功 能: 计算Y/X的反正切值
  用 法: double atan2(double y, double x);
  程序例:
  #include <stdio.h>
  #include <math.h>
  int main(void)
  {
  double result;
  double x = 90.0, y = 45.0;
  result = atan2(y, x);
  printf("The arc tangent ratio of %lf is %lf\n", (y / x), result);
  return 0;
  }
  c语言的用法: atexit
  功 能: 注册终止c语言的用法
  用 法: int atexit(atexit_t func);
  程序例:
  #include <stdio.h>
  #include <stdlib.h>
  void exit_fn1(void)
  {
  printf("Exit function #1 called\n");
  }
  void exit_fn2(void)
  {
  printf("Exit function #2 called\n");
  }
  int main(void)
  {
  /* post exit function #1 */
  atexit(exit_fn1);
  /* post exit function #2 */
  atexit(exit_fn2);
  return 0;
  }
  c语言的用法: atof
  功 能: 把字符串转换成浮点数
  用 法: double atof(const char *nptr);
  程序例:
  #include <stdlib.h>
  #include <stdio.h>
  int main(void)
  {
  float f;
  char *str = "12345.67";
  f = atof(str);
  printf("string = %s float = %f\n", str, f);
  return 0;
  }
  c语言的用法: atoi
  功 能: 把字符串转换成长整型数
  用 法: int atoi(const char *nptr);
  程序例:
  #include <stdlib.h>
  #include <stdio.h>
  int main(void)
  {
  int n;
  char *str = "12345.67";
  n = atoi(str);
  printf("string = %s integer = %d\n", str, n);
  return 0;
  }
  c语言的用法: atol
  功 能: 把字符串转换成长整型数
  用 法: long atol(const char *nptr);
  程序例:
  #include <stdlib.h>
  #include <stdio.h>
  int main(void)
  {
  long l;
  char *str = "98765432";
  l = atol(lstr);
  printf("string = %s integer = %ld\n", str, l);
  return(0);
  }
  c语言的用法: bar
  功 能: 画一个二维条形图
  用 法: void far bar(int left, int top, int right, int bottom);
  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, i;
  /* 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;
  /* loop through the fill patterns */
  for (i=SOLID_FILL; i<USER_FILL; i++)
  {
  /* set the fill style */
  setfillstyle(i, getmaxcolor());
  /* draw the bar */
  bar(midx-50, midy-50, midx+50,
  midy+50);
  getch();
  }
  /* clean up */
  closegraph();
  return 0;
  }
  c语言的用法: bar3d
  功 能: 画一个三维条形图
  用 法: void far bar3d(int left, int top, int right, int bottom,
  int depth, int topflag);
  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, i;
  /* initialize graphics, 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 error code */
  }
  midx = getmaxx() / 2;
  midy = getmaxy() / 2;
  /* loop through the fill patterns */
  for (i=EMPTY_FILL; i<USER_FILL; i++)
  {
  /* set the fill style */
  setfillstyle(i, getmaxcolor());
  /* draw the 3-d bar */
  bar3d(midx-50, midy-50, midx+50, midy+50, 10, 1);
  getch();
  }
  /* clean up */
  closegraph();
  return 0;
  }
  c语言的用法: bdos
  功 能: DOS系统调用
  用 法: int bdos(int dosfun, unsigned dosdx, unsigned dosal);
  程序例:
  #include <stdio.h>
  #include <dos.h>
  /* Get current drive as 'A', 'B', ... */
  char current_drive(void)
  {
  char curdrive;
  /* Get current disk as 0, 1, ... */
  curdrive = bdos(0x19, 0, 0);
  return('A' + curdrive);
  }
  int main(void)
  {
  printf("The current drive is %c:\n", current_drive());
  return 0;
  }
  c语言的用法: bdosptr
  功 能: DOS系统调用
  用 法: int bdosptr(int dosfun, void *argument, unsigned dosal);
  程序例:
  #include <string.h>
  #include <stdio.h>
  #include <dir.h>
  #include <dos.h>
  #include <errno.h>
  #include <stdlib.h>
  #define BUFLEN 80
  int main(void)
  {
  char buffer[BUFLEN];
  int test;
  printf("Enter full pathname of a directory\n");
  gets(buffer);
  test = bdosptr(0x3B,buffer,0);
  if(test)
  {
  printf("DOS error message: %d\n", errno);
  /* See errno.h for error listings */
  exit (1);
  }
  getcwd(buffer, BUFLEN);
  printf("The current directory is: %s\n", buffer);
  return 0;
  }
  c语言的用法: bioscom
  功 能: 串行I/O通信
  用 法: int bioscom(int cmd, char abyte, int port);
  程序例:
  #include <bios.h>
  #include <conio.h>
  #define COM1 0
  #define DATA_READY 0x100
  #define TRUE 1
  #define FALSE 0
  #define SETTINGS ( 0x80 | 0x02 | 0x00 | 0x00)
  int main(void)
  {
  int in, out, status, DONE = FALSE;
  bioscom(0, SETTINGS, COM1);
  cprintf("... BIOSCOM [ESC] to exit ...\n");
  while (!DONE)
  {
  status = bioscom(3, 0, COM1);
  if (status & DATA_READY)
  if ((out = bioscom(2, 0, COM1) & 0x7F) != 0)
  putch(out);
  if (kbhit())
  {
  if ((in = getch()) == '\x1B')
  DONE = TRUE;
  bioscom(1, in, COM1);
  }
  }
  return 0;
  }
  c语言的用法: biosdisk
  功 能: 软硬盘I/O
  用 法: int biosdisk(int cmd, int drive, int head, int track, int sector
  int nsects, void *buffer);
  程序例:
  #include <bios.h>
  #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;
  }
  c语言的用法: biosequip
  功 能: 检查设备
  用 法: int biosequip(void);
  程序例:
  #include <bios.h>
  #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;
  }
  c语言的用法: bioskey
  功 能: 直接使用BIOS服务的键盘接口
  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 0x08
  int 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;
  }
  c语言的用法: biosmemory
  功 能: 返回存储块大小
  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;
  }
  c语言的用法: biosprint
  功 能: 直接使用BIOS服务的打印机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;
  }
  c语言的用法: biostime
  功 能: 读取或设置BIOS时间
  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;
  }
  c语言的用法: brk
  功 能: 改变数据段空间分配
  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;
  }
  c语言的用法: 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;
  }
  c语言的用法: cabs
  功 能: 计算复数的绝对值
  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;
  }
  c语言的用法: calloc
  功 能: 分配主存储器
  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;
  }
  c语言的用法: 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;
  }
  c语言的用法: cgets
  功 能: 从控制台读字符串
  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;
  }
  c语言的用法: chdir
  功 能: 改变工作目录
  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;
  }
  c语言的用法: _chmod, chmod
  功 能: 改变文件的访问方式
  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);
  }
  c语言的用法: chsize
  功 能: 改变文件大小
  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;
  }
  c语言的用法: circle
  功 能: 在给定半径以(x, y)为圆心画圆
  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;
  }
  c语言的用法: cleardevice
  功 能: 清除图形屏幕
  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;
  }
  c语言的用法: clearerr
  功 能: 复位错误标志
  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;
  }
  c语言的用法: clearviewport
  功 能: 清除图形视区
  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;
  }
  c语言的用法: _close, close
  功 能: 关闭文件句柄
  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;
  }
  c语言的用法: clock
  功 能: 确定处理器时间
  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;
  }
  c语言的用法: closegraph
  功 能: 关闭图形系统
  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);
  outtextxy(x, y, "Press a key to close the graphics system:");
  /* wait for a key */
  getch();
  /* closes down the graphics system */
  closegraph();
  printf("We're now back in text mode.\n");
  printf("Press any key to halt:");
  getch();
  return 0;
  }
  c语言的用法: clreol
  功 能: 在文本窗口中清除字符到行末
  用 法: void clreol(void);
  程序例:
  #include <conio.h>
  int main(void)
  {
  clrscr();
  cprintf("The function CLREOL clears all characters from the\r\n");
  cprintf("cursor position to the end of the line within the\r\n");
  cprintf("current text window, without moving the cursor.\r\n");
  cprintf("Press any key to continue . . .");
  gotoxy(14, 4);
  getch();
  clreol();
  getch();
  return 0;
  }
  c语言的用法: clrscr
  功 能: 清除文本模式窗口
  用 法: void clrscr(void);
  程序例:
  #include <conio.h>
  int main(void)
  {
  int i;
  clrscr();
  for (i = 0; i < 20; i++)
  cprintf("%d\r\n", i);
  cprintf("\r\nPress any key to clear screen");
  getch();
  clrscr();
  cprintf("The screen has been cleared!");
  getch();
  return 0;
  }
  c语言的用法: coreleft
  功 能: 返回未使用内存的大小
  用 法: unsigned coreleft(void);
  程序例:
  #include <stdio.h>
  #include <alloc.h>
  int main(void)
  {
  printf("The difference between the highest allocated block and\n");
  printf("the top of the heap is: %lu bytes\n", (unsigned long) coreleft());
  return 0;
  }
  c语言的用法: cos
  功 能: 余弦c语言的用法
  用 法: double cos(double x);
  程序例:
  #include <stdio.h>
  #include <math.h>
  int main(void)
  {
  double result;
  double x = 0.5;
  result = cos(x);
  printf("The cosine of %lf is %lf\n", x, result);
  return 0;
  }
  c语言的用法: cosh
  功 能: 双曲余弦c语言的用法
  用 法: dluble cosh(double x);
  程序例:
  #include <stdio.h>
  #include <math.h>
  int main(void)
  {
  double result;
  double x = 0.5;
  result = cosh(x);
  printf("The hyperboic cosine of %lf is %lf\n", x, result);
  return 0;
  }
  c语言的用法: country
  功 能: 返回与国家有关的信息
  用 法: struct COUNTRY *country(int countrycode, struct country *country);
  程序例:
  #include <dos.h>
  #include <stdio.h>
  #define USA 0
  int main(void)
  {
  struct COUNTRY country_info;
  country(USA, &country_info);
  printf("The currency symbol for the USA is: %s\n",
  country_info.co_curr);
  return 0;
  }
  c语言的用法: cprintf
  功 能: 送格式化输出至屏幕
  用 法: int cprintf(const char *format[, argument, ...]);
  程序例:
  #include <conio.h>
  int main(void)
  {
  /* clear the screen */
  clrscr();
  /* create a text window */
  window(10, 10, 80, 25);
  /* output some text in the window */
  cprintf("Hello world\r\n");
  /* wait for a key */
  getch();
  return 0;
  }
  c语言的用法: cputs
  功 能: 写字符到屏幕
  用 法: void cputs(const char *string);
  程序例:
  #include <conio.h>
  int main(void)
  {
  /* clear the screen */
  clrscr();
  /* create a text window */
  window(10, 10, 80, 25);
  /* output some text in the window */
  cputs("This is within the window\r\n");
  /* wait for a key */
  getch();
  return 0;
  }
  c语言的用法: _creat creat
  功 能: 创建一个新文件或重写一个已存在的文件
  用 法: int creat (const char *filename, int permiss);
  程序例:
  #include <sys\stat.h>
  #include <string.h>
  #include <fcntl.h>
  #include <io.h>
  int main(void)
  {
  int handle;
  char buf[11] = "0123456789";
  /* change the default file mode from text to binary */
  _fmode = O_BINARY;
  /* create a binary file for reading and writing */
  handle = creat("DUMMY.FIL", S_IREAD | S_IWRITE);
  /* write 10 bytes to the file */
  write(handle, buf, strlen(buf));
  /* close the file */
  close(handle);
  return 0;
  }
  c语言的用法: creatnew
  功 能: 创建一个新文件
  用 法: int creatnew(const char *filename, int attrib);
  程序例:
  #include <string.h>
  #include <stdio.h>
  #include <errno.h>
  #include <dos.h>
  #include <io.h>
  int main(void)
  {
  int handle;
  char buf[11] = "0123456789";
  /* attempt to create a file that doesn't already exist */
  handle = creatnew("DUMMY.FIL", 0);
  if (handle == -1)
  printf("DUMMY.FIL already exists.\n");
  else
  {
  printf("DUMMY.FIL successfully created.\n");
  write(handle, buf, strlen(buf));
  close(handle);
  }
  return 0;
  }
  c语言的用法: creattemp
  功 能: 创建一个新文件或重写一个已存在的文件
  用 法: int creattemp(const char *filename, int attrib);
  程序例:
  #include <string.h>
  #include <stdio.h>
  #include <io.h>
  int main(void)
  {
  int handle;
  char pathname[128];
  strcpy(pathname, "\\");
  /* create a unique file in the root directory */
  handle = creattemp(pathname, 0);
  printf("%s was the unique file created.\n", pathname);
  close(handle);
  return 0;
  }
  c语言的用法: cscanf
  功 能: 从控制台执行格式化输入
  用 法: int cscanf(char *format[,argument, ...]);
  程序例:
  #include <conio.h>
  int main(void)
  {
  char string[80];
  /* clear the screen */
  clrscr();
  /* Prompt the user for input */
  cprintf("Enter a string with no spaces:");
  /* read the input */
  cscanf("%s", string);
  /* display what was read */
  cprintf("\r\nThe string entered is: %s", string);
  return 0;
  }
  c语言的用法: ctime
  功 能: 把日期和时间转换为字符串
  用 法: char *ctime(const time_t *time);
  程序例:
  #include <stdio.h>
  #include <time.h>
  int main(void)
  {
  time_t t;
  time(&t);
  printf("Today's date and time: %s\n", ctime(&t));
  return 0;
  }
  c语言的用法: ctrlbrk
  功 能: 设置Ctrl-Break处理程序
  用 法: void ctrlbrk(*fptr)(void);
  程序例:
  #include <stdio.h>
  #include <dos.h>
  #define ABORT 0
  int c_break(void)
  {
  printf("Control-Break pressed. Program aborting ...\n");
  return (ABORT);
  }
  int main(void)
  {
  ctrlbrk(c_break);
  for(;;)
  {
  printf("Looping... Press <Ctrl-Break> to quit:\n");
  }
  return 0;
  }
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