#include <stdlib.h>
#include <stdio.h>
#include <conio.h>

int main(void)
{
   char *string;
   double value;
   int dec, sign;
   int ndig = 10;

   clrscr();
   value = 9.876;
   string = ecvt(value, ndig, &dec, &sign);
   printf("string = %s      dec = %d \
   sign = %d\n", string, dec, sign);

   value = -123.45;
   ndig= 15;
   string = ecvt(value,ndig,&dec,&sign);
   printf("string = %s dec = %d sign = %d\n",
   string, dec, sign);
 

   value = 0.6789e5; /* scientific
   notation */
   ndig = 5;
   string = ecvt(value,ndig,&dec,&sign);
   printf("string = %s           dec = %d\
   sign = %d\n", string, dec, sign);

   return 0;
}
 
 

函数名: ellipse
功  能: 画一椭圆
用  法: void far ellipse(int x, int y, int stangle, int endangle,
    int xradius, int yradius);
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 = 0, endangle = 360;
   int xradius = 100, yradius = 50;

   /* 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 an error code */
   }

   midx = getmaxx() / 2;
   midy = getmaxy() / 2;
   setcolor(getmaxcolor());

   /* draw ellipse */
   ellipse(midx, midy, stangle, endangle,
    xradius, yradius);

   /* clean up */
   getch();
   closegraph();
   return 0;
}
 
 

函数名: enable
功  能: 开放硬件中断
用  法: void enable(void);
程序例:

/* ** NOTE:
This is an interrupt service routine. You can NOT compile this program
with Test Stack Overflow turned on and get an executable file which will
operate correctly.
*/

#include <stdio.h>
#include <dos.h>
#include <conio.h>

/* The clock tick interrupt */
#define INTR 0X1C

void interrupt ( *oldhandler)(void);

int count=0;

void interrupt handler(void)
{
/*
   disable interrupts during the handling of the interrupt
*/
   disable();
/* increase the global counter */
   count++;
/*
   re enable interrupts at the end of the handler
*/
   enable();
/* call the old routine */
   oldhandler();
}

int main(void)
{
/* save the old interrupt vector */
   oldhandler = getvect(INTR);

/* install the new interrupt handler */
   setvect(INTR, handler);

/* loop until the counter exceeds 20 */
   while (count < 20)
      printf("count is %d\n",count);

/* reset the old interrupt handler */
   setvect(INTR, oldhandler);

   return 0;
}
 
 

函数名: eof
功  能: 检测文件结束
用  法: int eof(int *handle);
程序例:

#include <sys\stat.h>
#include <string.h>
#include <stdio.h>
#include <fcntl.h>
#include <io.h>

int main(void)
{
   int handle;
   char msg[] = "This is a test";
   char ch;

   /* create a file */
   handle = open("DUMMY.FIL",
   O_CREAT | O_RDWR,
   S_IREAD | S_IWRITE);

   /* write some data to the file */
   write(handle, msg, strlen(msg));

   /* seek to the beginning of the file */
   lseek(handle, 0L, SEEK_SET);

   /*
      reads chars from the file until hit EOF
   */
   do
   {
      read(handle, &ch, 1);
      printf("%c", ch);
   } while (!eof(handle));

   close(handle);
   return 0;
}
 
 

函数名: exec...
功  能: 装入并运行其它程序的函数
用  法: int execl(char *pathname, char *arg0, arg1, ..., argn, NULL);
 int execle(char *pathname, char *arg0, arg1, ..., argn, NULL,
     char *envp[]);
 int execlp(char *pathname, char *arg0, arg1, .., NULL);
 int execple(char *pathname, char *arg0, arg1, ..., NULL,
      char *envp[]);
 int execv(char *pathname, char *argv[]);
 int execve(char *pathname, char *argv[], char *envp[]);
 int execvp(char *pathname, char *argv[]);
 int execvpe(char *pathname, char *argv[], char *envp[]);
程序例:

/* execv example */
#include <process.h>
#include <stdio.h>
#include <errno.h>

void main(int argc, char *argv[])
{
   int i;

   printf("Command line arguments:\n");
   for (i=0; i<argc; i++)
      printf("[%2d] : %s\n", i, argv[i]);

   printf("About to exec child with arg1 arg2 ...\n");
   execv("CHILD.EXE", argv);

   perror("exec error");

   exit(1);
}
 
 

函数名: exit
功  能: 终止程序
用  法: void exit(int status);
程序例:

#include <stdlib.h>
#include <conio.h>
#include <stdio.h>

int main(void)
{
   int status;

   printf("Enter either 1 or 2\n");
   status = getch();
   /* Sets DOS errorlevel  */
   exit(status - '0');

/* Note: this line is never reached */
   return 0;
}
 
 

函数名: exp
功  能: 指数函数
用  法: double exp(double x);
程序例:

#include <stdio.h>
#include <math.h>

int main(void)
{
   double result;
   double x = 4.0;

   result = exp(x);
   printf("'e' raised to the power \
   of %lf (e ^ %lf) = %lf\n",
   x, x, result);

   return 0;
}
 

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