Lesson 9。

09/Optional01.c

@@ -0,0 +1,41 @@
+#include <stdio.h>
+#include <stdbool.h>
+
+int history[1000] = {0};
+int nextIndex = 0;
+
+int inHistory(int num) {
+    int i = 0;
+    for (i = 0; i < nextIndex; i++) {
+        if (history[i] == num) {
+            return true;
+        }
+    }
+    return false;
+}
+
+int main() {
+    int input = 0;
+    int sum = 0;
+    int singleDigit = 0;
+    scanf("%d", &input);
+    do {
+        sum = 0;
+        while (input > 0) {
+            singleDigit = input % 10;
+            sum += singleDigit * singleDigit;
+            input /= 10;
+        }
+        input = sum;
+        if (inHistory(sum)) {
+            history[nextIndex] = 0;
+        }
+        else {
+            history[nextIndex] = sum;
+        }
+        nextIndex++;
+    }
+    while (history[nextIndex-1] > 1);
+    printf("%d\n", history[nextIndex-1]);
+    return 0;
+}