Question

how to write a cpp program that takes a number from a user, and print the sum of all numbers from one to that number on screen? using loop interation as basic as possible.

Answer 1

#include <iostream>
using namespace std;
int main() {
    cout<<"Enter the number"<<endl;
    int n; // variable n to be taken as input from user
    cin>>n; // taking the number as input from the user

    long long sum1 = 0; // to display the sum from 1 to n

    // 1st method - using for loop (iteration) 
    // time complexity of this method is O(n)

    for(int i = 1;i <= n; i++){
        sum1 += i;
    }


    cout <<"sum from method 1 is -> "<< sum1<<endl;
    
    // 2nd method - using maths
    // time complexity of this mehod is O(1)
    //mathematical formula to be used is sum = n*(n+1)/2;

    long long sum2 = n*(n+1)/2;

    cout <<"sum from method 2 is -> "<< sum2<<endl;


}

i have also attached the screenshot for the sample input and output.Thanks for the question. Happy Coding and Stay Safe.