add 4.12.c

1 files changed, 38 insertions, 0 deletions

diff --git a/4.12.c b/4.12.c
new file mode 100644
index 0000000..3e3e037
--- /dev/null
+++ b/4.12.c
@@ -0,0 +1,38 @@
+#include <stdio.h>
+
+#define MAXLEN 30
+
+char* itoa(char str[], int num);
+
+int 
+main(void)
+{
+  char str[MAXLEN];
+  int num;
+
+  num = -69420;
+
+  printf("%d\n", num);
+  printf("%s\n", itoa(str, num));
+
+  return 0;
+}
+
+char*
+itoa(char str[], int num)
+{
+  static int i = 0;
+
+  if (num < 0) {
+    num = -num;
+    str[i++] = '-';
+  }
+  
+  if (num/10)
+    itoa(str, num/10);
+
+  str[i++] = '0' + (num % 10);
+  str[i] = '\0';
+
+  return str;
+}