Added an Armstrong Number Checker file

CPP/algorithms/mathematical/armstrong_number.cpp

@@ -0,0 +1,65 @@
+/*
+Armstrong number: An Armstrong number is a number that is equal to the sum of its own 
+digits, each raised to the power of the total number of digits. 
+
+Author = Anuj Parwal
+*/
+#include<bits/stdc++.h>
+using namespace std;
+//Simple power function which is to be used later:
+long long int power(int base, int exp) {
+    long long int result = 1;
+    for (int i = 0; i < exp; i++) {
+        result *= base;
+    }
+    return result;
+}
+/*The following function checks whether or not the number provided is armstrong number or 
+not. If the number is an armstrong number, it will return 1 but if it isn't, 0 will be returned.
+*/
+int armstrong(long long int n){
+    int num_dig = 0;
+    long long int num_temp1 = n;
+    long long int num_temp2 = n;
+    for (int i = 0; i < 18; i++){
+        num_temp1/=10;
+        num_dig++;
+        if(num_temp1==0){
+            break;
+        }
+    }
+    /*Initialising sum, and then adding digits to the power of the number of digits to 
+    it*/
+    long long int sum = 0;
+    for (int i = 0; i < 18; i++){
+        int j = num_temp2%10;
+        sum += power(j, num_dig); 
+        num_temp2/=10;
+        if(num_temp2==0){
+            break;
+        }
+    }
+    //if it is an armstrong number, n=sum
+    if(sum==n){
+        return 1;
+    }
+    else{
+        return 0;
+    }
+}
+int main(){
+    //Initialising and taking input of number:
+    int n;
+    cout << "Enter your number here: ";
+    cin >> n;
+    int checker = armstrong(n);
+    if(checker==0){
+        cout << "No, it is not an armstrong number.";
+    }
+    else{
+        cout << "Yes, it is an Armstrong number.";
+    }
+    return 0;
+}
+/*Space Complexity = O(1)
+Time Complexity = O(n)*/