Hey guys I am extremely new so i need a help with my For Loop code

[dolma123]

So im trying to add the previous number to the next one like 1+2+3+4+5...+n,
when i put int a = 0; in the For loop it doesnt add it just displays like if i write 15 down there it just says
1
2
3
4
5...
if i put int a = 0; out of for it works fine, can someone help me understand this in and out thing?

  #include <iostream>
using namespace std;
int main()
{
    cout <<"Enter a number > " << flush;
    int b;
    cin >> b;
        int a = 0;

    for (int i = 0 ; i<b ;i = i+1 ){

        a=a+i;
        cout << a << endl;
    }







    return 0;

}

[Handy Andy]

Hello dolma123,

Welcome to the forum.

Defining "a" inside the for loop means that each iteration through the for loop will set "a" to zero before you use it.

Defining "a" outside the for loop means that you only define "a" once. Then when you change "a" inside the for loop it will always have a new value each iteration of the loop.

Hope that helps,

Andy

P.S. most generally the third part of the for loop i written i++. What you have will work, but i++ is the shorter more common version.

[dolma123]

OH MY GOD,
Thank you Andy you are right!!! Thank you for clearing my mind :3 <3

[jonnin]

see if
a+=i; instead of a = a+i gives what you expected, or a += a+i, depending on what you wanted?

or, maybe a better thing... can you tell us exactly what you think it should do ?

[dolma123]

Yeah i tried it its the same but it kinda makes me confused when i look at my code? maybe because im not familiar with it?

[jonnin]

what are you trying to make it do... trying to second guess isnt working :)

[Handy Andy]

Hello dolma123,

I put together these two versions of your original program in the hope that it helps you understand what is happening.

#include <iostream>

//  This version will show you the value of "a".
int main()
{
	//mstd::SetScreen();

	std::cout << "Enter a number > " << std::flush;
	int b;
	std::cin >> b;
	int a = 0;

	for (int i = 1; i <= b; i = i + 1)  // <--- Set i to start at 1. Changed the middle part to <= so i would catch the last number.
	{
		a += i;  // <--- Shorter version. Works the same.

		std::cout << a << std::endl;
	}

	//  Used to keep the console window open.
	std::cin.get();  // <--- Gets the \n left over from the first cin.
	std::cin.get();

	return 0;
}

////  This version will show you what is being added together to get your answer.
//int main()
//{
//	std::cout << "Enter a number > " << std::flush;
//	int b;
//	std::cin >> b;
//	int a = 0;
//
//	std::cout << "The result of adding ";
//
//	for (int i = 1; i <= b; i = i + 1)
//	{
//		a += i;
//
//		std::cout << i;
//		((i == b) ? std::cout << "" : std::cout << " + ");
//	}
//	std::cout << " is " << a << std::endl;
//
//      Used to keep the console window open.
	std::cin.get();  // <--- Gets the \n left over from the first cin.
	std::cin.get();//	return 0;
//} 

See what you think. Let me know if you have any questions.

Hope that helps,

Andy