Question

How to calculate sum of series 1 + 11 + 111 + 1111 + ... N in C++

Answer 1

#include <iostream>

// sum = 1 + 11 + 111 + 1111 + ... N 
 
long sum_of_series(int N) {
    long sum = 0, tmp = 1;
	
	for (int i = 0; i < N; i++) {
		std::cout << tmp << " ";
		
		if (i < N - 1)
			std::cout << "+ ";
		
		sum += tmp;
		tmp = (tmp * 10) + 1;		
	} 
	
	return sum;
}
 
int main()
{
    int N = 6;
    
    long sum = sum_of_series(N);

	std::cout << "= " << sum;
}
  
  
    
/*
run:
    
1 + 11 + 111 + 1111 + 11111 + 111111 = 123456
 
*/

 

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