start 5

1 files changed, 74 insertions, 0 deletions

diff --git a/5.1.c b/5.1.c
new file mode 100644
index 0000000..a0e0559
--- /dev/null
+++ b/5.1.c
@@ -0,0 +1,74 @@
+#include <stdio.h>
+#include <ctype.h>
+
+int getint(int *np);
+char getch(void);
+void ungetch(char input);
+
+int 
+main(void)
+{
+  int num;
+
+  getint(&num);
+
+  printf("%d\n", num);
+
+  return 0;
+}
+
+int 
+getint(int *np)
+{
+  int input, sign;
+
+  /* skip space */
+  while (isspace(input = getch()))
+    ;
+
+  if (!isdigit(input) && input != EOF && input != '+' && input != '-') {
+    ungetch(input);
+    return 0;
+  }
+
+  sign = (input == '-') ? -1 : 1;
+
+  if (input == '+' || input == '-')
+    while (isspace(input = getch()))
+     ;
+
+  for (*np = 0; isdigit(input); input = getch())
+    *np = *np * 10 + input - '0';
+
+  *np *= sign;
+
+  if (input != EOF)
+    ungetch(input);
+
+  /* return last digit or EOF */
+  return input;
+}
+
+static char buff = -1;
+
+char 
+getch(void)
+{
+  char temp;
+
+  if (buff == -1)
+    return getchar();
+
+  temp = buff;
+  buff = -1;
+  return temp;
+}
+
+void
+ungetch(char input)
+{
+  if (buff == -1)
+    buff = input;
+  else 
+    printf("Err: buffer is full\n");
+}