Thread: reading whole .txt file after entering numbers

hello

i am trying to make a program that will take numbers entered output them to a text file and compute the average and the standard deviation from the numbers in the file. I can enter the numbers fine and the program will write them to the file fine. I dont know how to make the program read all of the numbers that i have entered. the program will read the last number that i entered but nothing else. so like if i entered 3 numbers it would read only the last number i entered.

Code:

#include<iostream>
#include<fstream>
#include<cstdlib>
using namespace std;

void asknumbers(ofstream& myfile,int& howmanynumbers,double& numbers);
void readnumbers(ifstream& outfile, double numbers, double& total,int howmanynumbers);


int main()
{
	ofstream myfile;
	ifstream outfile;
	int howmanynumbers;
	double numbers,total;
	char repeat;

	do
	{
		

		myfile.open("numbers_file.txt",ios::trunc);			//opens and deletes everything from before
		myfile.close();										//closes file

		asknumbers(myfile,howmanynumbers,numbers);			//function for asking numbers
		readnumbers(outfile,numbers,total,howmanynumbers);
		
	

		cout<<"Do you want to repeat: ";
		cin>>repeat;
		

		system("cls");
	}while(repeat=='y'||repeat=='Y');						//end first do loop

	system("pause");
	return 0;
}



void asknumbers(ofstream& myfile,int& howmanynumbers,double& numbers)
{

	cout<<"how many numbers do you want to input:";			//asks how many number i want to put in
	cin>>howmanynumbers;

	int numbercounter;
	numbercounter=howmanynumbers;

		do													//asks for the numbers
		{

			cout<<"enter the numbers:";
			cin>>numbers;

			myfile.open ("numbers_file.txt",ios::app);		//writes to file called numbers_file.txt
			myfile<<numbers<<endl;							//writes numbers to the file
			myfile.close();									//closes file

			numbercounter--;								//counts down how many numbers put in

		}while(numbercounter>=1);							//ends asking for numbers
}


void readnumbers(ifstream& outfile,double numbers, double& total,int howmanynumbers)
{
	total=0;
	outfile.open("numbers_file.txt");						//opens file
	for(int x=howmanynumbers;x>0;x--)
	{
	
		outfile>>numbers;										//reads numbers
	}
	total+=numbers;						//calculates total from numbers input
	cout<<"The total of the numbers is: "<<total<<endl;

}

readnumbers is reading all of the numbers, but each time it executes the line

Code:

outfile>>numbers;

the previous entry is overwritten by the next one so you're not doing anything with any but the last entry. The line

Code:

total += numbers:

should be inside the for loop.

Also, in your asknumbers function, instead of opening and closing the file on every iteration of the do-while loop, you should open the file just once before the loop, and close it after the loop.

Thanks

I have another question about how i would calculate the standard deviation...
I know that the standard deviation is calculated as:
sqrt((n1-avg)^2+(n2-avg)^2+(n3-avg)^2+...)/howmanynumbers) right?
I guess my question is how would I get my program to get the n1,n2,n3, variables and so on into that equation?
I have this

Code:

void standarddev(ifstream& outfile, double numbers,double average,double& standardd,int howmanynumbers)
{
	outfile.open("numbers_file.txt");								//opens file
	for(int x=howmanynumbers;x>0;x--)
	{
		standardd=sqrt(pow((numbers-average),2)/average);
	}
	cout<<"The standard deviation of those numbers is: "<<standardd<<endl;
}

but I dont think its right, could I get some help