How to print a triangle using user-defined coordinates?

[CopaceticCoffee]

I have to write a program that takes three sets of user-given coordinates (x1, y1), (x2, y2), (x3, y3) and prints a right triangle using these coordinates on a grid. Right now I have:

int x1, y1, x2, y2, x3, y3;

cout << "Please enter the triangle's coordinates: ";
cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;

base = x2 - x1;
height = y3 - y2;

for(int i = height; i >= 1; ++i)
    {
        for(int j = base; j >= 1; ++j)
        {
            cout << j << " ";
        }
        cout << "\n";
    }

This results in a bombardment of increasing numbers when I run the program. Can someone help point me in the right direction? I know how to print out a basic triangle using for loops but I am struggling with getting this to work with user defined coordinates.

[48T7M4Gy]

Why not show us the whole program if it's not too long? And some sample output.

line 1: doesn't make any sense if you are declaring the variable
lines 6 and 7: base and height aren't declared

[CopaceticCoffee]

Oh wow, I can't believe I typed line 1 like that. That's not how it is in my actual program. I fixed it. Here's my program:

#include <iostream>

using namespace std;

int main(){

int x1, y1, x2, y2, x3, y3;

cout << "Please enter the triangle's coordinates: ";
cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;

int base = x2 - x1;
int height = y2 - y1;

for(int i = height; i >= 1; ++i)
    {
        for(int j = base; j >= 1; ++j)
        {
            cout << j << " ";
        }
        cout << "\n";
    }
return 0;
}

My logic is, I'm sure, way off. I hope there's enough here to work with.

[CopaceticCoffee]

What I really need help with is the for loops. I can fix my math for finding base and height, but once I do, I need a better understanding of how to work with those variables in the for loops to print out a triangle properly.

[48T7M4Gy]

OK that's better. So to save us a lot of time what's say you hard code the values for the coordinates and edit that post. Just comment out the cin on line 10 - don't delete it and add a couple of lines x1 = whatever etc

[CopaceticCoffee]

Here's the updated code with hardcoded variables:

#include <iostream>

using namespace std;

int main(){

int x1 = 0, 
     y1 = 0, 
     x2 = 4, 
     y2 = 0, 
     x3 = 4, 
     y3 = 4;

//cout << "Please enter the triangle's coordinates: ";
// cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;

int base = x2 - x1;
int height = y2 - y1;

for(int i = height; i >= 1; ++i)
    {
        for(int j = base; j >= 1; ++j)
        {
            cout << j << " ";
        }
        cout << "\n";
    }
return 0;
}

[48T7M4Gy]

Good

[48T7M4Gy]

I'm still trying to work out what you're supposed to be doing but here's a start. Look carefully at what of changed. > vs < , the values of base and height are suss too so print them out is a good move or use a debugger.

Printing blank spaces is a bad move because you don't get feedback while you're testing.

It's starting to make sense though.

#include <iostream>

using namespace std;

int main(){
    
    int x1 = 0,
    y1 = 0,
    x2 = 4,
    y2 = 0,
    x3 = 4,
    y3 = 4;
    
    //cout << "Please enter the triangle's coordinates: ";
    // cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
    
    int base = x2 - x1;
    int height = y2 - y1;
    
    for(int i = 0; i < 5; ++i)
    {
        for(int j = 0; j < 5; ++j)
        {
            cout << i << "*";
        }
        cout << "\n";
    }
    return 0;
}

[48T7M4Gy]

So far, height = 0 !!
int height = y3 - y2; !!

[48T7M4Gy]

#include <iostream>

using namespace std;

int main(){
    
    int x1 = 0,
    y1 = 0,
    x2 = 4,
    y2 = 0,
    x3 = 3,
    y3 = 4;
    
    //cout << "Please enter the triangle's coordinates: ";
    // cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
    
    int base = x2 - x1;
    int height = y3 - y2;
    
    cout << "base " << base << " height " << height << '\n';
    
    for(int i = 0; i < base; ++i)
    {
        for(int j = i; j < height; ++j)
        {
            cout << i << "*";
        }
        cout << "\n";
    }
    return 0;
}

base 4 height 4
0*0*0*0*
1*1*1*
2*2*
3*
Program ended with exit code: 0

This probably gives you enough to play arround with. :)

[CopaceticCoffee]

Thank you so much for your help! This has given me a great start. I will play around with the code :)

[48T7M4Gy]

y1 and x3 aren't used - they would be used if the base and height aren't aligned with the x,y axes. In which case the nested loop would need to be substantially modified - best check that you are/are not required to program for that.

[keskiverto]

user-given coordinates (x1, y1), (x2, y2), (x3, y3) and prints a right triangle using these coordinates on a grid.

I'm a user. I give coordinates: 42 42 42 42 42 42
I'm disappointed, I did expect to see a triangle on the quintillion * quintillion grid.

In other words, what do we know about the grid? Barely large enough to fit the triangle?
(For my input, a 42*42 would be enough.)

Where is the (0,0)? Top left, bottom left, center? Is (0,1) above or below (0,0)?

I enter three points. What if I change the order of the points? Should the image change?

What to do about aliasing?


The task (as written) gives the user "freedom". That in turn means that the program/programmer must have more answers.