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CS1201: Programming Language 2

By : Nouf Almunyif. CS1201: Programming Language 2. Recursion. Recursion and Recursive Functions. Main calls another function…..normal A function calls another function2….normal A function calls itself ?! Possible?? YES  A recursive function is one that call itself. General form.

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CS1201: Programming Language 2

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  1. By: Nouf Almunyif CS1201: Programming Language 2 Recursion

  2. Recursion and Recursive Functions • Main calls another function…..normal • A function calls another function2….normal • A function calls itself ?! Possible?? • YES A recursive function is one that call itself.

  3. General form void recurse() { recurse(); //Function calls itself }

  4. Finding Factorial 5! = 5*4*3*2*1 5! 5! Final value=120 5!=5*24=120 returned 5*4! 5*4! 4!=4*6=24 returned 4*3! 4*3! 3!=3*2=6 returned 3*2! 3*2! 2!=2*1=2 returned 2*1! 2*1! 1 1 1

  5. Finding Factorial • #incloud <iostream>; • Using nampespace std; • Void main() { • intn,factorial,i; • cout << "Enter a positive integer: "; • cin >> n; • for (i = 1; i <= n; i++) • { if (i == 1) • factorial = 1; • Else • factorial = factorial * i; • } • cout << "The factorial of " << n << " is " << factorial << endl; • }

  6. Finding Factorial Recursively Enter a positive integer : 4 //Recursive factorial Function #include<iostream> Int factorial(intN); Void main() {int num; cout<<“Enter a positive integer:”; cin>>num; cout<<“factorial=“<<factorial(num); } Int factorial( int N) { if ( N <= 1) //the base case return 1; else return N * factorial (N - 1); } Factorial = 24 N=4 Retrun 4 *factorial(3) 6 4*6=24 N=3 Retrun 3 *factorial(2) 2 3*2 =6 N=2 Retrun 2 *factorial(1) 2*1 = 2 1 N=1 Retrun 1

  7. Example printing number counting doun void main() { int input; cout<<"enter positive number "; cin>>input; myMethod(input); } #include <iostream> using namespace std; voidmyMethod( int counter) { if(counter == 0) return; // no value returning just for EXIT the function else { cout<<counter<<endl; myMethod(--counter); return; // no value returning just for EXIT the function } }

  8. Exercise • write a recursion function to printint number counting up: 1,2,3,4,5 …. N. • Test your function and show the out put

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