Homework Question (Program posted)

[CompSciLoser]

Hello,
I'm in a C++ programming class. We were given the assignment to "Write a program that asks the user for a positive integer value. The program should use a loop
to get the sum of all the integers from 1 up to the number entered. For example, if the user
enters 50, the loop will find the sum of 1, 2, 3, 4, ... 50.  
Input Validation: Do not accept a negative starting number."

Here is what I have so far.

  #include <iostream>
using namespace std;
int main()
{
	int sum = 0;
	int num;
	
	cout << "Enter a positive number:\n";
	cin >> num;
	
	for (int x = 0; x <= num; x++)

	{
		sum = sum + num;
		x++;
	}
		if (num < 1)
	{
		cout << "\n" << num << " is an invalid input.";
		cout << " Please enter a positive integer.\n";
	}
		else
		cout << "\nThe sum of numbers 1 through " << num
		<< " " << "is " << sum << endl;
		
		return 0;
}

I don't know where I messed up or went wrong, but whenever I enter the number to test the code, I'm not getting the write answer. For instance, whenever I enter "2" the code should tell me 3, but instead it says 4.

Can someone please tell me where I went wrong.

[TheKingOfTyrants]

Do not accept a negative starting number.

You need to concentrate on this first. This means you should not proceed until the user gives you a positive number. You check to see if the number entered is negative or positive on line 17, but that needs to occur immediately after the user inputs a number and the for-loop you should use needs to occur within the else block of that check.

As far as calculating the number, you need to add the values of x to sum each time instead of num.

Your program flow should look like so:
1. Get input from user.
2. If user inputs a negative number, tell them and do nothing (or keep pestering them until they do as I say :P).
3. Else, loop between [1, num], adding each increment to sum and output result.

[whitenite1]

@CompSciLoser

Also, because you have an x++; in your for loop, you will be adding every other number, since you are increasing the value of x without using it. Leave that (x++;) out of the loop.

[Charles1992]

Also, try sum += x; in your loop. At the moment you are adding your input every iteration. For example, when are inputting 2 the code is adding 2+2. Skipping a step inbetween. The code has 3 iterations because you are starting from 0 but going to == num and therefore have num+1 iterations.