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<P><font color="#003399">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: </font>
<P><font color="#003399">#include <stdio.h> <BR>
#include <math.h> </font>
<P><font color="#003399">int main(void) <BR>
{ <BR>
struct complex z; <BR>
double val; </font>
<P><font color="#003399"> z.x = 2.0; <BR>
z.y = 1.0; <BR>
val = cabs(z); </font>
<P><font color="#003399"> printf("The absolute value of %.2lfi %.2lfj
is %.2lf", z.x, z.y, val); <BR>
return 0; <BR>
} <BR>
<BR>
<BR>
</font>
<P><font color="#003399">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: </font>
<P><font color="#003399">#include <stdio.h> <BR>
#include <alloc.h> </font>
<P><font color="#003399">int main(void) <BR>
{ <BR>
char *str = NULL; </font>
<P><font color="#003399"> /* allocate memory for string */ <BR>
str = calloc(10, sizeof(char)); </font>
<P><font color="#003399"> /* copy "Hello" into string */ <BR>
strcpy(str, "Hello"); </font>
<P><font color="#003399"> /* display string */ <BR>
printf("String is %s\n", str); </font>
<P><font color="#003399"> /* free memory */ <BR>
free(str); </font>
<P><font color="#003399"> return 0; <BR>
} <BR>
<BR>
<BR>
</font>
<P><font color="#003399">函数名: ceil <BR>
功 能: 向上舍入 <BR>
用 法: double ceil(double x); <BR>
程序例: </font>
<P><font color="#003399">#include <math.h> <BR>
#include <stdio.h> </font>
<P><font color="#003399">int main(void) <BR>
{ <BR>
double number = 123.54; <BR>
double down, up; </font>
<P><font color="#003399"> down = floor(number); <BR>
up = ceil(number); </font>
<P><font color="#003399"> 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); </font>
<P><font color="#003399"> return 0; <BR>
} <BR>
<BR>
<BR>
</font>
<P><font color="#003399">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: </font>
<P><font color="#003399">#include <stdio.h> <BR>
#include <conio.h> </font>
<P><font color="#003399">int main(void) <BR>
{ <BR>
char buffer[83]; <BR>
char *p; </font>
<P><font color="#003399"> /* There's space for 80 characters plus
the NULL terminator */ <BR>
buffer[0] = 81; </font>
<P><font color="#003399"> 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);
</font>
<P><font color="#003399"> /* Leave room for 5 characters plus the
NULL terminator */ <BR>
buffer[0] = 6; </font>
<P><font color="#003399"> 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>
</font>
<P><font color="#003399">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: </font>
<P><font color="#003399">#include <stdio.h> <BR>
#include <stdlib.h> <BR>
#include <dir.h> </font>
<P><font color="#003399">char old_dir[MAXDIR]; <BR>
char new_dir[MAXDIR]; </font>
<P><font color="#003399">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); </font>
<P><font color="#003399"> if (chdir("\\")) <BR>
{ <BR>
perror("chdir()"); <BR>
exit(1); <BR>
} </font>
<P><font color="#003399"> if (getcurdir(0, new_dir)) <BR>
{ <BR>
perror("getcurdir()"); <BR>
exit(1); <BR>
} <BR>
printf("Current directory is now: \\%s\n", new_dir); </font>
<P><font color="#003399"> printf("\nChanging back to orignal directory:
\\%s\n", old_dir); <BR>
if (chdir(old_dir)) <BR>
{ <BR>
perror("chdir()"); <BR>
exit(1); <BR>
} </font>
<P><font color="#003399"> return 0; <BR>
} <BR>
<BR>
</font>
<P><font color="#003399">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: </font>
<P><font color="#003399">#include <sys\stat.h> <BR>
#include <stdio.h> <BR>
#include <io.h> </font>
<P><font color="#003399">void make_read_only(char *filename); </font>
<P><font color="#003399">int main(void) <BR>
{ <BR>
make_read_only("NOTEXIST.FIL"); <BR>
make_read_only("MYFILE.FIL"); <BR>
return 0; <BR>
} </font>
<P><font color="#003399">void make_read_only(char *filename) <BR>
{ <BR>
int stat; </font>
<P><font color="#003399"> 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>
</font>
<P><font color="#003399">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: </font>
<P><font color="#003399">#include <string.h> <BR>
#include <fcntl.h> <BR>
#include <io.h> </font>
<P><font color="#003399">int main(void) <BR>
{ <BR>
int handle; <BR>
char buf[11] = "0123456789"; </font>
<P><font color="#003399"> /* create text file containing 10 bytes
*/ <BR>
handle = open("DUMMY.FIL", O_CREAT); <BR>
write(handle, buf, strlen(buf)); </font>
<P><font color="#003399"> /* truncate the file to 5 bytes in size
*/ <BR>
chsize(handle, 5); </font>
<P><font color="#003399"> /* close the file */ <BR>
close(handle); <BR>
return 0; <BR>
} <BR>
<BR>
</font>
<P><font color="#003399">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: </font>
<P><font color="#003399">#include <graphics.h> <BR>
#include <stdlib.h> <BR>
#include <stdio.h> <BR>
#include <conio.h> </font>
<P><font color="#003399">int main(void) <BR>
{ <BR>
/* request auto detection */ <BR>
int gdriver = DETECT, gmode, errorcode; <BR>
int midx, midy; <BR>
int radius = 100; </font>
<P><font color="#003399"> /* initialize graphics and local variables
*/ <BR>
initgraph(&gdriver, &gmode, ""); </font>
<P><font color="#003399"> /* 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>
} </font>
<P><font color="#003399"> midx = getmaxx() / 2; <BR>
midy = getmaxy() / 2; <BR>
setcolor(getmaxcolor()); </font>
<P><font color="#003399"> /* draw the circle */ <BR>
circle(midx, midy, radius); </font>
<P><font color="#003399"> /* clean up */ <BR>
getch(); <BR>
closegraph(); <BR>
return 0; <BR>
} <BR>
<BR>
<BR>
</font>
<P><font color="#003399">函数名: cleardevice <BR>
功 能: 清除图形屏幕 <BR>
用 法: void far cleardevice(void); <BR>
程序例: </font>
<P><font color="#003399">#include <graphics.h> <BR>
#include <stdlib.h> <BR>
#include <stdio.h> <BR>
#include <conio.h> </font>
<P><font color="#003399">int main(void) <BR>
{ <BR>
/* request auto detection */ <BR>
int gdriver = DETECT, gmode, errorcode; <BR>
int midx, midy; </font>
<P><font color="#003399"> /* initialize graphics and local variables
*/ <BR>
initgraph(&gdriver, &gmode, ""); </font>
<P><font color="#003399"> /* read result of initialization */ <BR>
errorcode = graphresult(); <BR>
if (errorcode != grOk) /* an error occurred */ <BR>
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