Reverse integer

Signed-off-by: begeekmyfriend <[email protected]>

007_reverse_integer/Makefile

@@ -0,0 +1,2 @@
+all:
+	gcc -O2 -o test reverse_integer.c

007_reverse_integer/reverse_integer.c

@@ -0,0 +1,47 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <limits.h>
+
+static int reverse(int x)
+{
+    int y = 0;
+    while (x != 0) {
+        int n = x % 10;
+        // Checking the over/underflow.
+        // Actually, it should be y>(INT_MAX-n)/10, but n/10 is 0, so omit it.
+        if (y > INT_MAX / 10 || y < INT_MIN / 10) {
+            return 0;
+        }
+        y = y * 10 + n;
+        x /= 10;
+    }
+    return y;
+}
+
+#define TEST(n, e)  printf("%12d  =>  %-12d  %s!\n",  n, reverse(n),  e == reverse(n)?"passed":"failed")
+
+int main(int argc, char**argv)
+{
+    //basic cases
+    TEST(  123,  321);
+    TEST( -123, -321);
+    TEST( -100,   -1);
+    TEST( 1002, 2001);
+    //big integer
+    TEST( 1463847412,  2147483641);
+    TEST(-2147447412, -2147447412);
+    TEST( 2147447412,  2147447412);
+    //overflow
+    TEST( 1000000003, 0);
+    TEST( 2147483647, 0);
+    TEST(-2147483648, 0);
+    //customized cases
+    if (argc != 2) {
+        fprintf(stderr, "Usage: ./test i\n");
+        return 0;
+    }
+    printf("\n");
+    int n = atoi(argv[1]); 
+    printf("%12d  =>  %-12d  %s!\n",  n, reverse(n), reverse(reverse(n))==n ? "passed":"failed");
+    return 0;
+}