add answer plus minor tweaks

Author: fsaadatmand

chapter03/3-4.c

@@ -3,70 +3,74 @@
  * itoa does not handle the largest negative number, that is, the value of n
  * equal to -(2^wordsize-1). Explain why not. Modify it to print that value
  * correctly, regardless of the machine on which it runs. 
- * By Faisal Saadatmand
+ *
+ * Answer: In two's complement number representation, the limit ranges from
+ * -(2^wordsize-1) to (2^wordsize-1)-1. The most significant bit is the sign
+ *  bit; however, it also holds a value for negative numbers; thus, making the
+ *  negative limit larger than the positive limit by a value of 1. This makes a
+ *  binary value of -(2^wordsize-1) equal to 2^wordsize-1, which is larger than
+ *  (2^wordsize-1)-1. For example, in a 8-bit wordsize, -128 and 128 are
+ *  represented as 0x80, which is larger than what the largest positive number
+ *  an 8-bit word can hold, 127 or 0x8f.  The itoa function's first assignment
+ *  instruction is to negate n. In the case n is
+ * -(2^worldsize-1), the negation will produce the same binary number, and
+ *  therefore, the algorithm will fails at the do/while loop.  
+ *
+ *  By Faisal Saadatmand
  */
 
 #include <stdio.h>
 #include <string.h>
 #include <limits.h>
 
-/* functions */
-void reverse(char []);
-void itoa(int, char []);
-
-/* reverse function: reverse string s in place */
-void reverse(char s[])
-{
-	int c, i, j;
+#define MAXLEN 100
 
-	for (i = 0, j = strlen(s) - 1; i < j; i++, j --) {
-		c = s[i];
-		s[i] = s[j];
-		s[j] = c;
-	}
-}
+void itoa(int, char []);
+void reverse(char []);
 
 /* itoa: convert n to characters in s */
 void itoa(int n, char s[])
 {
-	int i, sign, lastDigit;
+	int i, sign;
 
-	lastDigit = 0;
-	if (n == INT_MIN) {                   /* add check for size */
-		lastDigit = (n % 10 * -1) + '0';  /* extract save the last digit */
-		n -= 1;                           /* reduce n to fit INT_MAX */
+	i = 0;
+	if ((sign = n) < 0) {
+		s[i++] = -(n % 10) + '0';   /* extract last digit */
+		n /= 10;                    /* reduce value to fit signed int */
+		n = -n;                     /* negate value */ 
 	}
 
-	if ((sign = n) < 0)                   /* record sign */
-		n = -n;
-
-	i = 0;
-	do {                                  /* generate digits in reverse order */
-		s[i++] = n % 10 + '0';            /* get next digit */
+	do {
+		s[i++] = n % 10 + '0';
 	} while ((n /= 10) > 0);
-
 	if (sign < 0)
 		s[i++] = '-';
 
-	if (lastDigit > 0)                    /* put back saved last digit */
-		s[0] = lastDigit;
-
 	s[i] = '\0';
-
 	reverse(s);
 }
 
+void reverse(char s[])
+{
+	int c, i, j;
+
+	for (i = 0, j = strlen(s) - 1; i < j; i++, j--) {
+		c = s[i];
+		s[i] = s[j];
+		s[j] = c;
+	}
+}
+
 int main(void)
 {
+	char string[MAXLEN];
 	int intValue;
-	char stringNumber[64];
 
-	printf("Enter integer to convert to a string: ");
+	printf("Enter an integer to convert in a string (range: %i to %i):\n",
+			INT_MIN, INT_MAX);
 	scanf("%i", &intValue);
-
-	itoa(intValue, stringNumber);
-
-	printf("%s\n", stringNumber);
+	itoa(intValue, string);
+	printf("%s\n", string);
 
 	return 0;
 }