Merge pull request #473 from siddhi-244/Siddhi/first_index

Added first index of an element in array

Author: smv1999

README.md

@@ -26,6 +26,7 @@ This repository contains all the popular Competitive Programming questions and I
  <li><a href="https://github.com/smv1999/CompetitiveProgrammingQuestionBank/tree/master/Numbers">Numbers</a></li>
  <li><a href="https://github.com/smv1999/CompetitiveProgrammingQuestionBank/tree/master/OOPs">OOPs</a></li>
  <li><a href="https://github.com/smv1999/CompetitiveProgrammingQuestionBank/tree/master/Passwords">Passwords</a></li>
+ <li><a href="https://github.com/smv1999/CompetitiveProgrammingQuestionBank/tree/master/Recursion">Recursion</a></li>
  <li><a href="https://github.com/smv1999/CompetitiveProgrammingQuestionBank/tree/master/Searching%20Algorithms">Searching Algorithms</a></li>
  <li><a href="https://github.com/smv1999/CompetitiveProgrammingQuestionBank/tree/master/Sorting%20Algorithms">Sorting Algorithms</a></li>
  <li><a href="https://github.com/smv1999/CompetitiveProgrammingQuestionBank/tree/master/Standard%20Template%20Library">Standard Template Library</a></li>

Recursion/first_index_of_element_in_array.cpp

@@ -0,0 +1,37 @@
+/*Program to find first index of a number in array*/
+#include <iostream>
+using namespace std;
+int firstIndex(int arr[],int n,int x){
+  if(n==0){ //if size of array is 0 
+    return -1;
+  }
+  if(arr[0]==x){ //if the element is found on first index 
+    return 0;
+  }
+  int ans=firstIndex(arr+1,n-1,x);//recursion
+  if(ans==-1){
+    return -1;
+  }
+  else{
+    return ans+1;
+  }
+}
+
+int main() {
+  int n,x,a[200];
+  cin>>n;
+  for(int i=0;i<n;i++){
+    cin>>a[i];
+  }
+  cin>>x;
+  cout<<firstIndex(a,n,x);
+  
+}
+/*Example
+Input:
+5
+5 5 6 7 9
+5
+Output:
+0 
+*/