add 4.13.c

1 files changed, 66 insertions, 0 deletions

diff --git a/4.13.c b/4.13.c
new file mode 100644
index 0000000..b470a13
--- /dev/null
+++ b/4.13.c
@@ -0,0 +1,66 @@
+#include <stdio.h>
+#include <string.h>
+
+#define MAXLEN 15
+
+void reverse(char str[], size_t left, size_t right);
+char* itoa(int n, char str[]);
+void swap(char array[], int i, int j);
+
+int 
+main(void)
+{
+  int n = 42069;
+  char str[MAXLEN];
+
+  printf("%d\n", n);
+  printf("%s\n", itoa(n, str));
+
+  return 0;
+}
+
+void
+reverse(char str[], size_t left, size_t right)
+{
+  if (left >= right)
+    return;
+
+  swap(str, left, right);
+  reverse(str, left+1, right-1); 
+}
+
+char*
+itoa(int n, char str[])
+{
+  int sign, i;
+
+  /* to include the most -ve int */
+  n = ((sign = n) < 0) ? -(n+1) : n-1;
+
+  i = 0;
+  do {
+    str[i++] = n%10 + '0';
+  } while ((n /= 10) > 0);
+
+  if (sign <0)
+    str[i++] = '-';
+
+  /* part of "to include the most -ve int" */
+  str[0] += 1;
+  str[i] = '\0';
+
+  reverse(str, 0, strlen(str)-1);
+
+  return str;
+}
+
+void
+swap(char array[], int i, int j)
+{
+  int temp;
+
+  temp = array[i];
+
+  array[i] = array[j];
+  array[j] = temp;
+}