To find the sum of Given Arithmetic progression

Question - 

Given an Arithmetic progression , we have to find the sum of progression till n element.

Example - 

Input : arr[] = {1, 2, 3} n = 10

Output : 55

Approach - 

We calculate the sum using standard formula.

Implementation - 

//sum of given arithmetic progression

#include<iostream>

using namespace std;

void sum(int arr[],int n)

{

int a=arr[0];

int d=arr[1]-arr[0];

int sum;

sum=(n*(2*a+(n-1)*d))/2;

cout<<"Sum is : "<<sum<<endl;

}

int main(int argc, char *argv[])

{

int n;

cout<<"Enter n : ";cin>>n;

int arr[3];

cout<<"Enter first 3 elements : "<<endl;

for(int i=0;i<3;i++)

cin>>arr[i];

sum(arr,n);

return 0;

}

code on compiler

Time complixity - O(1)