函數(shù)名: cabs 
功 能: 計(jì)算復(fù)數(shù)的絕對(duì)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(shù)名: calloc 
功 能: 分配主存儲(chǔ)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(shù)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(shù)名: cgets 
功 能: 從控制臺(tái)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(shù)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(shù)名: _chmod, chmod 
功 能: 改變文件的訪問(wèn)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(shù)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(shù)名: circle 
功 能: 在給定半徑以(x, y)為圓心畫(huà)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(shù)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(shù)名: clearerr 
功 能: 復(fù)位錯(cuò)誤標(biāo)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(shù)名: clearviewport 
功 能: 清除圖形視區(qū) 
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(shù)名: _close, close 
功 能: 關(guān)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); 
}