ex_5-1.c

   1 #include <stdio.h>
   2 #include <ctype.h>
   3
   4 #define BUFSIZE 100
   5
   6 char buf[BUFSIZE];
   7 int bufp = 0;
   8
   9 /*
  10
  11 NOTE: getchar and ungetch work in tandem:
  12
  13 This allows the user to get a character from standard in, have a look at it
  14 and then determine to use it or place it back into a buffer for later use.
  15
  16 If this buffer has any chars inside, thise will be poped off first
  17 before getting more input from stdin.
  18
  19 */
  20
  21 int getch(void);
  22 void ungetch(int);
  23
  24 /* reads from buffer if buffer contains chars or calls getchar otherwise */
  25 int getch(void)
  26 {
  27         return (bufp > 0) ? buf[--bufp] : getchar();
  28 }
  29
  30 /* places pushed-back characters into a char array shared buffer */
  31 void ungetch(int c)
  32 {
  33         if(bufp >= BUFSIZE)
  34                 printf("ungetch: too many characters\n");
  35         else
  36                 buf[bufp++] = c;
  37 }
  38
  39 /* get next integer from input and put into *pn */
  40 int getint(int *pn)
  41 {
  42         int c, sign, signed_num;
  43
  44         while(isspace(c = getch()))
  45                 ;
  46         if(!isdigit(c) && c != EOF && c != '+' && c != '-')
  47         {
  48                 ungetch(c);
  49                 return 0;
  50         }
  51
  52         sign = (c == '-') ? -1 : 1;
  53         if((signed_num = (c == '+' || c == '-')))
  54                 c = getch();
  55         if(!isdigit(c))
  56         {
  57                 ungetch(c);
  58                 if(signed_num)
  59                         ungetch((sign == -1) ? '-' : '+');
  60                 return 0;
  61         }
  62
  63         for(*pn = 0; isdigit(c); c = getch())
  64                 *pn = 10 * *pn + (c - '0');
  65         *pn *= sign;
  66         if(c != EOF)
  67                 ungetch(c);
  68         return c;
  69 }
  70
  71 int main()
  72 {
  73         int n[5];
  74         int retval = '\0';
  75
  76         retval = getint(n);
  77
  78         printf("Retval: %c\n", retval);
  79
  80         int i;
  81         for(i = 0; i < 5; i++)
  82         {
  83                 printf("%d", n[i]);
  84         }
  85
  86
  87         printf("\n");
  88
  89         return 1;
  90 }