Description:
Recursion in c/c++this is a very detailed tutorial in which we will learn what is recursion and how to recursion function to find the factorial of a number
without any further delay, let’s get started
What is recursion in c/c++:
function that calls itself is known as a recursive function and this technique is known as recursion so recursion in c/c++ is basically the process of rebuilding items in a similar way and in terms of programming especially recursive functions the function gives a call to itself based on certain criteria so this enables the function to repeat itself several times outputting the result at the end of each iteration kind of like a for loop or any other looping control structure and the recursion continues until some condition is met so that it prevents infinite recursion right so in even in for loop while loop we have a condition wherein the for the control is exited outside the loop similarly in recursive functions there has to be a condition after which the recursion should stop so sometimes ifelse condition is used inside okay so this was a little bit about recursive functions.
Example: calculate the sum of first n natural numbers so natural numbers start from 1 to infinity so I want to calculate the sum of first three numbers
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 
#include<iostream> using namespace std; int sum(int num) { if(num !=0) return (num + sum(num1)); else return num; } int main() { int n; cout<<”enter number: ”; cin>>n; int total = sum(n); cout<<endl<<”the sum is: ”<<n<<total<<endl; return 0; } 
Program explanation of recursion in c/c++:
you can see on line number 3 we have the signature of prototype of the function you can see return type is int sum is the name of the function and it is taking one integer value so this is the upper limit of the number of numbers that you want to calculate the sum off so if you want to calculate from one two three you enter three so inside the function you can see it’s saying if num not equal to zero that is if the number is not equal to zero then you have to return num plus sum of num minus 1 so you can see in yellow the sum is called inside the sum function itself so this is a recursive call that is inside the sum function and calling again the sum function with a new argument which is one less than what the number we first and if the num is equal to zero then return that number as it is so this is that if else condition which prevents the infinite recursion in c/c++programming and in the main function what I’m doing is I’m declaring a integer variable int n I am saying enter number till which you want to tell you till where you want the sum of natural numbers to be calculated then I take the input from the user and then I create one more integer variable int total I’ll say in total and say sum and I pass that number so if the user enters 3 I pass 3 over the function and since the recursive function returns an integer value you can see total equal to sum so the integer value returned would be assigned to the total integer variable that’s how return types work right so in the end I say the sum is and the number which entered by the user and I print out the total.
The difference between iteration and recursion in c/c++
Recursion 
Iteration 
Function calls itself  Functions loops some part of code 
Recursion is a selection structure  Iteration is a repetition structure 
Recursion achieves repetition through repeated method calls  Iteration explicitly uses repetition structures 
Recursion terminate when a base case is recognized  Iteration terminates when the loop continuation condition fails 
Recursion invokes the function repeatedly and hence the overhead of method
calls can be costly in both processing time and memory space

Iteration repeatedly executes code this can be less expensive in both processor time and memory space 
Infinite recursion occurs if the recursion step does not reduce the problem in a manner that converges on the base case  An infinite loop occurs with iteration it the loop continuation test never become false 
Recursion returns value to the calling function  Iteration does not return value 
Recursion makes code smaller  Iteration makes the code longer 
Infinite recursion can crash the system  Infinite looping uses CPU cycles repeatedly 
Recursion is a slower process  Iteration is faster. 
Example: write a program which finds the factorial of a number using recursion function
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 
#include<iostream.h> #include<conio.h> void main() { int a; cout<<”Enter the number :”; cin>>a; cout<<”Factorial = ”<<fact(a); getch(); } long int fact(int n) { if(n==0) return(1); else return(n * fact(n1)); } 
Program explanation of recursion in c/c++:
we write a function fact which in turn called the same function because during the calculation of factorial we can say that n factorial is equals n into n minus 1 factorial for defining the function we are using a function name as fact which takes an integer parameter as n and returns a result as a long value which will be the factorial value of n in the function definition we are checking whether the value of n is zero so if the value of n is zero we return the result as 1 because 0 factorial is 1 as if the value of n is more than 0 we calculate the result as n into factorial of n minus 1 and that value will be returned so this is an example for a recursion in c /c++ function.