fstream question in program

[warscoten]

I have been trying for a while to figure out how to put my program together where it writes to a file the height of a projectile.

The exact problem is stated as this: Write a program that writes to a file a table that shows the height of a projectile launched straight up for each second from launch time (time zero) until the projectile hits the ground. The last entry in the table should show a projectile height of 0. The height after t seconds is given by: s = (in. velocity)* t - .5gt^2 where g is 9.8m/s^2.
The program should prompt the user for the launch velocity.


My program so far is:


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

const g=9.8;

int main()
{
ofstream outfile( "table.txt", ios::on ); // is this supposed to be on or out?
double launch velocity, lv;
double time, t;
double height, h;

cout << "Enter speed of launch velocity(m/s) and receive the height after a certain number of seconds. => ";

cin >> lv;


h = ((lv * t) - (.5 * g *(t ^ t)))


outfile << h;


cout << "The position of the projectile during second intervals is .....";


outfil.close();

return 0;
}


I want the txt file that will be created to be called table. My problem is that I am not sure of what I need to add to have my equation write data to a txt file. And also if you see any other mistakes that I have made in the program or from the directions please tell me. I am a beginner so I might not understand all the lingo and more advanced stuff.

Please excuse the format of my program because I am not too sure how to put it in code form like it is supposed to, so if you can tell me that would be great.

Thank you

[coder777]

See http://www.cplusplus.com/reference/iostream/ofstream/ for the flags in the constructor. You might need only one parameter. Depends on what you want.

h = ((lv * t) - (.5 * g *(t ^ 2))) ; is missing. ^ is bit wise or. What you need is pow() http://www.cplusplus.com/reference/clibrary/cmath/pow/

[code]Your code[/code]

[firedraco]

What you need is pow()

In this case, don't even bother. Just use t * t, pow is for tricky stuff like 2^(7.3)

[warscoten]

Ok. I fixed the t in the equation. I already looked at those links, but since I am a beginner, they didn't make too much sense to me. I understand what the fstream function does, but I am confused on how to implement into the program to use the velocity input and equation to write to a file. Any one else want to help?

[warscoten]

Anybody want to answer this question?

[matsom]

how to implement into the program to use the velocity input and equation to write to a file.

First figure out what data(s) you want to output, then figure out how you want to present it to the user, e.g taking newton's F = ma, we want to present it to the user how the F changes with the increase of mass and ask user for a starting value of m, and use a = 10m/s²:

Enter a start value for m: //this is std::cout
5
For m = 5 until m = 20, using a = 10ms^(-2): //std::cout until the end of loop
 m      F
 5     50
10    100
15    150
20    200

How you write it into your file is how you write it to screen using std::cout

[zb0S216C]

const g=9.8;
This isn't quite complete.

double launch velocity, lv;
Something is missing between launch and velocity.

ofstream's are structures that output data to a file as standard. You could remove ios::on / ios::out and see if anything new arises.

[warscoten]

The problem is I don't know how to write it onto a file. Can anyone help me with the questions in my main post and not just vaguely explain roundabout answers?

[matsom]

...vaguely explain roundabout answers?

1. "How you write it into your file is how you write it to screen using std::cout" I think this is pretty direct.

2. You've been here long enough already to know
- that people who respond to your posts will never give a complete solution to assignment questions
- there'll always be a reminder to post your codes to show what you've done/already knew

3. here's a (much) less roundabout way to explain #1:

//using iostream
#include <iostream>
using namespace std;
int main()
{
    cout << "Hello world" << endl; //print text to screen, start the next print at the next line
    cout << 123456789 << endl; //print numbers to screen
    return 0;
}

//using fstream
#include <fstream>
using namespace std;
int main()
{
    ofstream fout("out.txt"); //default mode is enough for most cases
    fout << "Hello world" << endl; //print text into file, start the next print at the next line
    fout << 123456789 << endl; //print numbers into file
    fout.close();
    return 0;
}