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<P>函数名: cabs
<BR>功 能: 计算复数的绝对值
<BR>用 法: double cabs(struct complex z);
<BR>程序例:
<P>#include <stdio.h>
<BR>#include <math.h>
<P>int main(void)
<BR>{
<BR> struct complex z;
<BR> double val;
<P> z.x = 2.0;
<BR> z.y = 1.0;
<BR> val = cabs(z);
<P> printf("The absolute value of %.2lfi %.2lfj is %.2lf",
z.x, z.y, val);
<BR> return 0;
<BR>}
<BR>
<BR>
<BR>
<P>函数名: calloc
<BR>功 能: 分配主存储器
<BR>用 法: void *calloc(size_t nelem, size_t elsize);
<BR>程序例:
<P>#include <stdio.h>
<BR>#include <alloc.h>
<P>int main(void)
<BR>{
<BR> char *str = NULL;
<P> /* allocate memory for string */
<BR> str = calloc(10, sizeof(char));
<P> /* copy "Hello" into string */
<BR> strcpy(str, "Hello");
<P> /* display string */
<BR> printf("String is %s\n", str);
<P> /* free memory */
<BR> free(str);
<P> return 0;
<BR>}
<BR>
<BR>
<BR>
<P>函数名: ceil
<BR>功 能: 向上舍入
<BR>用 法: double ceil(double x);
<BR>程序例:
<P>#include <math.h>
<BR>#include <stdio.h>
<P>int main(void)
<BR>{
<BR> double number = 123.54;
<BR> double down, up;
<P> down = floor(number);
<BR> up = ceil(number);
<P> printf("original number %5.2lf\n",
number);
<BR> printf("number rounded down %5.2lf\n", down);
<BR> printf("number rounded up %5.2lf\n", up);
<P> return 0;
<BR>}
<BR>
<BR>
<BR>
<P>函数名: cgets
<BR>功 能: 从控制台读字符串
<BR>用 法: char *cgets(char *str);
<BR>程序例:
<P>#include <stdio.h>
<BR>#include <conio.h>
<P>int main(void)
<BR>{
<BR> char buffer[83];
<BR> char *p;
<P> /* There's space for 80 characters plus the NULL terminator
*/
<BR> buffer[0] = 81;
<P> printf("Input some chars:");
<BR> p = cgets(buffer);
<BR> printf("\ncgets read %d characters: \"%s\"\n", buffer[1],
p);
<BR> printf("The returned pointer is %p, buffer[0] is at %p\n",
p, &buffer);
<P> /* Leave room for 5 characters plus the NULL terminator
*/
<BR> buffer[0] = 6;
<P> printf("Input some chars:");
<BR> p = cgets(buffer);
<BR> printf("\ncgets read %d characters: \"%s\"\n", buffer[1],
p);
<BR> printf("The returned pointer is %p, buffer[0] is at %p\n",
p, &buffer);
<BR> return 0;
<BR>}
<BR>
<BR>
<BR>
<P>函数名: chdir
<BR>功 能: 改变工作目录
<BR>用 法: int chdir(const char *path);
<BR>程序例:
<P>#include <stdio.h>
<BR>#include <stdlib.h>
<BR>#include <dir.h>
<P>char old_dir[MAXDIR];
<BR>char new_dir[MAXDIR];
<P>int main(void)
<BR>{
<BR> if (getcurdir(0, old_dir))
<BR> {
<BR> perror("getcurdir()");
<BR> exit(1);
<BR> }
<BR> printf("Current directory is: \\%s\n", old_dir);
<P> if (chdir("\\"))
<BR> {
<BR> perror("chdir()");
<BR> exit(1);
<BR> }
<P> if (getcurdir(0, new_dir))
<BR> {
<BR> perror("getcurdir()");
<BR> exit(1);
<BR> }
<BR> printf("Current directory is now: \\%s\n", new_dir);
<P> printf("\nChanging back to orignal directory: \\%s\n",
old_dir);
<BR> if (chdir(old_dir))
<BR> {
<BR> perror("chdir()");
<BR> exit(1);
<BR> }
<P> return 0;
<BR>}
<BR>
<BR>
<P>函数名: _chmod, chmod
<BR>功 能: 改变文件的访问方式
<BR>用 法: int chmod(const char *filename, int permiss);
<BR>程序例:
<P>#include <sys\stat.h>
<BR>#include <stdio.h>
<BR>#include <io.h>
<P>void make_read_only(char *filename);
<P>int main(void)
<BR>{
<BR> make_read_only("NOTEXIST.FIL");
<BR> make_read_only("MYFILE.FIL");
<BR> return 0;
<BR>}
<P>void make_read_only(char *filename)
<BR>{
<BR> int stat;
<P> stat = chmod(filename, S_IREAD);
<BR> if (stat)
<BR> printf("Couldn't make %s read-only\n",
filename);
<BR> else
<BR> printf("Made %s read-only\n", filename);
<BR>}
<BR>
<BR>
<BR>
<P>函数名: chsize
<BR>功 能: 改变文件大小
<BR>用 法: int chsize(int handle, long size);
<BR>程序例:
<P>#include <string.h>
<BR>#include <fcntl.h>
<BR>#include <io.h>
<P>int main(void)
<BR>{
<BR> int handle;
<BR> char buf[11] = "0123456789";
<P> /* create text file containing 10 bytes */
<BR> handle = open("DUMMY.FIL", O_CREAT);
<BR> write(handle, buf, strlen(buf));
<P> /* truncate the file to 5 bytes in size */
<BR> chsize(handle, 5);
<P> /* close the file */
<BR> close(handle);
<BR> return 0;
<BR>}
<BR>
<BR>
<P>函数名: circle
<BR>功 能: 在给定半径以(x, y)为圆心画圆
<BR>用 法: void far circle(int x, int y, int radius);
<BR>程序例:
<P>#include <graphics.h>
<BR>#include <stdlib.h>
<BR>#include <stdio.h>
<BR>#include <conio.h>
<P>int main(void)
<BR>{
<BR> /* request auto detection */
<BR> int gdriver = DETECT, gmode, errorcode;
<BR> int midx, midy;
<BR> int radius = 100;
<P> /* initialize graphics and local variables */
<BR> initgraph(&gdriver, &gmode, "");
<P> /* read result of initialization */
<BR> errorcode = graphresult();
<BR> if (errorcode != grOk) /* an error occurred */
<BR> {
<BR> printf("Graphics error: %s\n", grapherrormsg(errorcode));
<BR> printf("Press any key to halt:");
<BR> getch();
<BR> exit(1); /* terminate with an error
code */
<BR> }
<P> midx = getmaxx() / 2;
<BR> midy = getmaxy() / 2;
<BR> setcolor(getmaxcolor());
<P> /* draw the circle */
<BR> circle(midx, midy, radius);
<P> /* clean up */
<BR> getch();
<BR> closegraph();
<BR> return 0;
<BR>}
<BR>
<BR>
<BR>
<P>函数名: cleardevice
<BR>功 能: 清除图形屏幕
<BR>用 法: void far cleardevice(void);
<BR>程序例:
<P>#include <graphics.h>
<BR>#include <stdlib.h>
<BR>#include <stdio.h>
<BR>#include <conio.h>
<P>int main(void)
<BR>{
<BR> /* request auto detection */
<BR> int gdriver = DETECT, gmode, errorcode;
<BR> int midx, midy;
<P> /* initialize graphics and local variables */
<BR> initgraph(&gdriver, &gmode, "");
<P> /* read result of initialization */
<BR> errorcode = graphresult();
<BR> if (errorcode != grOk) /* an error occurred */
<BR> {
<BR> printf("Graphics error: %s\n", grapherrormsg(errorcode));
<BR> printf("Press any key to halt:");
<BR> getch();
<BR> exit(1); /* terminate with an error
code */
<BR> }
<P> midx = getmaxx() / 2;
<BR> midy = getmaxy() / 2;
<BR> setcolor(getmaxcolor());
<P> /* for centering screen messages */
<BR> settextjustify(CENTER_TEXT, CENTER_TEXT);
<P> /* output a message to the screen */
<BR> outtextxy(midx, midy, "press any key to clear the screen:");
<P> /* wait for a key */
<BR> getch();
<P> /* clear the screen */
<BR> cleardevice();
<P> /* output another message */
<BR> outtextxy(midx, midy, "press any key to quit:");
<P> /* clean up */
<BR> getch();
<BR> closegraph();
<BR> return 0;
<BR>}
<BR>
<BR>
<BR>
<P>函数名: clearerr
<BR>功 能: 复位错误标志
<BR>用 法:void clearerr(FILE *stream);
<BR>程序例:
<P>#include <stdio.h>
<P>int main(void)
<BR>{
<BR> FILE *fp;
<BR> char ch;
<P> /* open a file for writing */
<BR> fp = fopen("DUMMY.FIL", "w");
<P> /* force an error condition by attempting to read */
<BR> ch = fgetc(fp);
<BR> printf("%c\n",ch);
<P> if (ferror(fp))
<BR> {
<BR> /* display an error message */
<BR> printf("Error reading from DUMMY.FIL\n");
<P> /* reset the error and EOF indicators
*/
<BR> clearerr(fp);
<BR> }
<P> fclose(fp);
<BR> return 0;
<BR>}
<BR>
<BR>
<BR>
<P>函数名: clearviewport
<BR>功 能: 清除图形视区
<BR>用 法: void far clearviewport(void);
<BR>程序例:
<P>#include <graphics.h>
<BR>#include <stdlib.h>
<BR>#include <stdio.h>
<BR>#include <conio.h>
<P>#define CLIP_ON 1 /* activates clipping in viewport */
<P>int main(void)
<BR>{
<BR> /* request auto detection */
<BR> int gdriver = DETECT, gmode, errorcode;
<BR> int ht;
<P> /* initialize graphics and local variables */
<BR> initgraph(&gdriver, &gmode, "");
<P> /* read result of initialization */
<BR> errorcode = graphresult();
<BR> if (errorcode != grOk) /* an error occurred */
<BR> {
<BR> printf("Graphics error: %s\n", grapherrormsg(errorcode));
<BR> printf("Press any key to halt:");
<BR> getch();
<BR> exit(1); /* terminate with an error
code */
<BR> }
<P> setcolor(getmaxcolor());
<BR> ht = textheight("W");
<P> /* message in default full-screen viewport */
<BR> outtextxy(0, 0, "* <-- (0, 0) in default viewport");
<P> /* create a smaller viewport */
<BR> setviewport(50, 50, getmaxx()-50, getmaxy()-50, CLIP_ON);
<P> /* display some messages */
<BR> outtextxy(0, 0, "* <-- (0, 0) in smaller viewport");
<BR> outtextxy(0, 2*ht, "Press any key to clear viewport:");
<P> /* wait for a key */
<BR> getch();
<P> /* clear the viewport */
<BR> clearviewport();
<P> /* output another message */
<BR> outtextxy(0, 0, "Press any key to quit:");
<P> /* clean up */
<BR> getch();
<BR> closegraph();
<BR> return 0;
<BR>}
<BR>
<BR>
<BR>
<P>函数名: _close, close
<BR>功 能: 关闭文件句柄
<BR>用 法: int close(int handle);
<BR>程序例:
<P>#include <string.h>
<BR>#include <stdio.h>
<BR>#include <fcntl.h>
<BR>#include <io.h>
<P>main()
<BR>{
<BR> int handle;
<BR> char buf[11] = "0123456789";
<P> /* create a file containing 10 bytes */
<BR> handle = open("NEW.FIL", O_CREAT);
<BR> if (handle > -1)
<BR> {
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