AWK solution for week 84, part 1.

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+#
+# You are given an integer $N.
+#
+# Write a script to reverse the given integer and print the result.
+# Print 0 if the result doesn't fit in 32-bit signed integer.
+# 
+# The number 2,147,483,647 is the maximum positive value for a 32-bit
+# signed binary integer in computing.
+# 
+
+#
+# This is two challenges in one. First, we have to reverse a given
+# integer -- which in AWK we do character by character.
+#
+# For the second part, we have to compare it against a given
+# maximum value. Awk, or at least my version, handles big integers
+# just fine.
+#
+# There's a tiny thing to consider. 2,147,483,647 is the largest
+# positive value which fits in a 32-bit signed integer, but the
+# smallest integer which fits is -2,147,483,648 [1]. So, if the input
+# is 8463847412, the output should 0, but if the input is -8463847412,
+# the output should be -2147483648.
+#
+# [1] We're assuming 2s-complement integers, which seems to have
+#     been the norm for the past 50 years or so.
+#
+
+{
+    low     = 0;     # Indicates lower bound for reversing
+    reverse = "";    # This will contain the reversed number.
+
+    #
+    # Check whether the number starts with a hyphen; if so, 
+    # keep the sign, and don't include it in the part which
+    # needs reversing.
+    #
+    if (substr ($0, 1, 1) == "-") {
+        reverse = "-";
+        low     = 1;
+    }
+
+    #
+    # Do the actual reversal. Note that in AWK strings are 1-based,
+    # and, hence, length() gives the highest index.
+    #
+    for (i = length ($0); i > low; i --) {
+        reverse = reverse substr ($0, i, 1);
+    }
+    #
+    # Turn reverse into a number
+    #
+    reverse = reverse + 0;
+
+    #
+    # Check wether it fits in a 32-bit integer (we assume 2's complement)
+    #
+    if (reverse < -2147483648 || reverse > 2147483647) {
+        reverse = 0;
+    }
+    print reverse;
+}