Use C++ to Print a Floyd triangle - c++

Question

I'm trying to build a program which will accept numbers from user and create Floyd triangle.
I tried using the logic of Floyd triangle, but its printing as a line.
Example:
Enter total numbers: 5
Enter the numbers: 3,8,2,4,9
O/p:
3
82
249
Here's my code:
#include <iostream>
using namespace std;
int main()
{
int totalnos, j, i;
cout << "Enter total numbers: ";
cin >> totalnos;
int numbers[totalnos];
cout << "Enter the numbers: ";
for (i = 1; i <= totalnos; i++)
{
cin >> numbers[i];
}
for (i = 1; i <= totalnos; i++)
{
for (j = 1; j <= 1; j++)
{
cout << numbers[i];
}
}
}

Answer 1

You have a problem with the kind of loops shown below. I don't know wether this kind of solution is due to you coming from the Pascal world, or because you've seen it elsewhere. Anyway, you should not make loops start in 1 and go to i, or at least, you should take into account that in the C-like world (C, C++, Java, C#, and many others), arrays start at index 0, and end at index n - 1, being n the size of the array.
int numbers[totalnos];
cout << "Enter the numbers: ";
for (i = 1; i <= totalnos; i++)
{
cin >> numbers[i];
}
The problem is actually not what indexes you use for loops, but that you must always use 0..n-1 when accessing arrays. So you can change your loop to just access the array correctly:
int numbers[totalnos];
cout << "Enter the numbers: ";
for (i = 1; i <= totalnos; i++)
{
cin >> numbers[ i - 1 ];
}
Or you can do as all programmers in the C-like world, and directly start your indexes at 0:
int numbers[totalnos];
cout << "Enter the numbers: ";
for (i = 0; i < totalnos; i++)
{
cin >> numbers[i];
}
Instead of going from 1 to totalnos, now you go from 0 to totalnos - 1 (notice the i < totalnos instead of the i <= totalnos, that's a sutil change).
You were accessing memory past the limit of the array, which means that your program will show undefined behaviour (this means that it will probably crash, though under some conditions, nothing seems to happen, which is even more dangerous).
Now the algorithm itself. I haven't heard about the Floyd triangle. It seems that it is built with the natural numbers starting from 1. However, you are asking for totalnos numbers. You will need more than totalnos numbers in order to build a Floyd triangle with totalnos rows. That's why you need to adjust the position of the number being shown taking into account the number of columns for each row (numPos starts with 0).
cout << endl;
for (i = 0; i < totalnos; i++)
{
if ( ( totalnos - i ) < numPos ) {
numPos = totalnos - i;
}
for (j = 0; j < i; j++)
{
cout << numbers[numPos] << ' ';
++numPos;
}
cout << endl;
}
You can find the whole code here: http://ideone.com/HhjFpz
Hope this helps.

Answer 2

Internal loop can be modified as below :
for (i=0; i < 3; i++)
{
for (j=0; j<=i; j++)
{
cout << numbers[i+j];
}
cout<<" ";
}
Hard coded value "3" can be replaced with the "number of rows of Floyd triangle .
I think this will do the trick .

Answer 3

In inner loop you made mistake with j <= 1; should be j <= i;
And you missed '\n' char for new line.
Here is fix:
#include <iostream>
using namespace std;
int main()
{
int totalnos, j, i, k = 0;
cout << "Enter total numbers: ";
cin >> totalnos;
//int numbers[totalnos];
//cout << "Enter the numbers: ";
// for (i = 1; i <= totalnos; i++)
// {
// cin >> numbers[i];
// }
for (i = 1; i <= totalnos; i++)
{
// your code for (j = 1; j <= 1; j++)
for(j=1; j<=i; ++j) // fixed
cout << k+j << ' ';
++k;
cout << endl; // fix
}
}