chore(CPlusPlus): add armstrong (#455)

Co-authored-by: Rahul Rajeev Pillai <66192267+Ashborn-SM@users.noreply.github.com>

algorithms/CPlusPlus/Maths/armstrong.cpp

@@ -0,0 +1,30 @@
+#include <iostream>
+using namespace std;
+int main ()
+{
+  int a = 0, t, n, s, r, p, i, sum = 0;
+  cin >> n;
+  t = n;
+  while (t > 0)
+    {
+      t /= 10;
+      a++;
+    }
+  s = n;
+  while (s > 0)
+    {
+      r = s % 10;
+      p = r;
+      for (i = 1; i < a; i++)
+    {
+      p *= r;
+    }
+      sum += p;
+      s /= 10;
+    }
+  if (sum == n)
+    cout << n << " is an armstrong number.";
+  else
+    cout << n << " is not an armstrong number.";
+  return 0;
+}

algorithms/CPlusPlus/README.md

@@ -118,6 +118,7 @@
 2. [Prime Number](Maths/prime-check.cpp)
 3. [Prime Sieve](Maths/prime-sieve.cpp)
 4. [Fibonacci Series](Maths/fibonaccci-series.cpp)
+5. [Armstrong Number](Maths/armstrong.cpp)
 
 # Recursion