chore(CPlusPlus): add reverse number algorithm (#789)

Co-authored-by: Arsenic <54987647+Arsenic-ATG@users.noreply.github.com>

algorithms/C/maths/fibonacci-number/src/fib.c

@@ -1,4 +1,4 @@
-#include"fib.h"
+#include"./fib.h" // NOLINT(build/include)
 #include<math.h> // sqrt, pow are used in binet_fib
 
 int recur_fib(int n){

algorithms/C/maths/fibonacci-number/src/fib.h

@@ -1,5 +1,6 @@
-#ifndef FIB_H_INCLUDED
-#define FIB_H_INCLUDED
+
+#ifndef ALGORITHMS_C_MATHS_FIBONACCI_NUMBER_SRC_FIB_H_
+#define ALGORITHMS_C_MATHS_FIBONACCI_NUMBER_SRC_FIB_H_
 
 /**
  * fib(n) takes nonnegative number n
@@ -19,4 +20,4 @@ int iter_log_fib(int n);
 int log_fib(int n);
 int binet_fib(int n);
 
-#endif
+#endif  // ALGORITHMS_C_MATHS_FIBONACCI_NUMBER_SRC_FIB_H_"

algorithms/C/maths/fibonacci-number/src/main.c

@@ -1,5 +1,5 @@
 #include<stdio.h>
-#include"fib.h"
+#include"./fib.h" // NOLINT(build/include)
 
 int main(){
 	memomizing_fib(); // this is to initialize the memomized table

algorithms/CPlusPlus/README.md

@@ -186,6 +186,7 @@
 - [Product of two numbers](Recursion\product-of-numbers.cpp)
 - [Product of digits in a number](Recursion\product-of-digits.cpp)
 - [Linear search using recursion](Recursion/linear-search.cpp)
+- [Reverse a number using recursion](Recursion/reverse-a-number.cpp)
 
 ## Number System
 

algorithms/CPlusPlus/Recursion/reverse-a-number.cpp

@@ -0,0 +1,34 @@
+/*
+Description: Program to reverse integer using recursion
+Time complexity: O(n) where n is the number of digits in the integer
+*/
+
+#include <cmath>
+#include <iostream>
+using namespace std;
+
+int Helper(int n ,int base , int ans)
+{
+    if(n < 1)
+        return ans;
+    ans = ans * base + (n % 10);    // Update the ans for every digit
+    return Helper(n / 10, base , ans);    
+}
+
+int Rev(int n)
+{
+    return Helper(n , 10, 0);
+}
+
+
+int main(int argc, char const *argv[])
+{   
+    cout << Rev(13579);
+
+    return 0;
+}
+/*
+Input: 13579
+Output: 97531
+*/
+