Spacing for Right aligned Triangle - c++

Question

Assignment:
Write a program that prompts the user for an integer value representing the height of a triangle. The program should then print out a triangle of O’s of that height, with a vertically aligned right edge.
My problem:
I have figured out the code to execute a normal triangle, but I am having some difficulty on writing code to have spacing before my "0's" to make it aligned to the right.
#include <iostream>
using namespace std;
int main()
{
int triHeight;
int c = 0;
int r = 0;
int k = 0;
cout << "Enter the triangle height: " << endl;
cin >> triHeight;
for (c = 0; c <= triHeight; c = c+1)
{
for (r = 0; r < c; r = r + 1)
{
cout << "0";
}
for (k = 0; k <= c; k = k - 1)
{
cout << " ";
}
cout << endl;
}
system("pause");
return 0;
}

Answer 1

You have two main problems :
you write the spaces after the 0 rather than before to have the 0 indented
for (k = 0; k <= c; k = k - 1) never ends up to the possible effect of an overflow
I also encourage you to check the result of >> to be sure a valid integer was enter so like if (!(cin >> triHeight)) cerr << "invalid height" << endl; else { ... }
A right way close to yours using loops for all is (supposing you want a pyramid) :
#include <iostream>
using namespace std;
int main()
{
int triHeight;
cout << "Enter the triangle height: " << endl;
if (!(cin >> triHeight))
cerr << "invalid height" << endl;
else {
for (int h = 1; h <= triHeight; h += 1) {
for (int s = triHeight - h; s != 0; s -= 1)
cout << ' ';
for (int z = 2*(h-1)+1; z >0; z -=1)
cout << '0';
cout << endl;
}
}
}
Compilation and execution :
/tmp % g++ -pedantic -Wextra -Wall c.cc
/tmp % ./a.out
Enter the triangle height:
5
0
000
00000
0000000
000000000
/tmp %
If you want half a pyramid :
#include <iostream>
using namespace std;
int main()
{
int triHeight;
cout << "Enter the triangle height: " << endl;
if (!(cin >> triHeight))
cerr << "invalid height" << endl;
else {
for (int h = 1; h <= triHeight; h += 1) {
for (int s = triHeight - h; s != 0; s -= 1)
cout << ' ';
for (int z = 0; z < h; z += 1)
cout << '0';
cout << endl;
}
}
}
Compilation and execution :
/tmp % g++ -pedantic -Wall -Wextra c.cc
/tmp % ./a.out
Enter the triangle height:
5
0
00
000
0000
00000
/tmp %
You can also do not make the two internal loops by yourself :
#include <iostream>
using namespace std;
int main()
{
int triHeight;
cout << "Enter the triangle height: " << endl;
if (!(cin >> triHeight))
cerr << "invalid height" << endl;
else {
for (int h = 1; h <= triHeight; h += 1)
cout << string(triHeight - h, ' ') << string(h, '0') << endl;
}
}
Compilation and execution :
/tmp % g++ -pedantic -Wall -Wextra c.cc
/tmp % ./a.out
Enter the triangle height:
5
0
00
000
0000
00000
/tmp %
that solution is shorter but creates temporary strings

Answer 2

The logic of your program is wrong. At first you are trying to output the symbol 'O'
for (r = 0; r < c; r = r + 1)
{
cout << "0";
}
and after that you are trying to output spaces
for (k = 0; k <= c; k = k - 1)
{
cout << " ";
}
Moreover this loop is invalid because the variable k is decremented starting from 0.
The program can be written using only one loop and standard i/o manipulators declared in the header <iomanip>
Here is a demonstrative program
#include <iostream>
#include <iomanip>
int main()
{
while ( true )
{
const char c = 'O';
std::cout << "Enter the height of a triangle (0 - exit): ";
int height = 0;
if ( not ( std::cin >> height ) or ( height <= 0 ) ) break;
std::cout << '\n';
for ( int i = 0; i < height; i++ )
{
std::cout << std::setw( height - i ) << std::setfill( ' ' ) << c;
std::cout << std::setw( i + 1 ) << std::setfill( c ) << '\n';
}
std::cout << '\n';
}
return 0;
}
The program output might look the following way
Enter the height of a triangle (0 - exit): 1
O
Enter the height of a triangle (0 - exit): 2
O
OO
Enter the height of a triangle (0 - exit): 3
O
OO
OOO
Enter the height of a triangle (0 - exit): 4
O
OO
OOO
OOOO
Enter the height of a triangle (0 - exit): 5
O
OO
OOO
OOOO
OOOOO
Enter the height of a triangle (0 - exit): 6
O
OO
OOO
OOOO
OOOOO
OOOOOO
Enter the height of a triangle (0 - exit): 7
O
OO
OOO
OOOO
OOOOO
OOOOOO
OOOOOOO
Enter the height of a triangle (0 - exit): 8
O
OO
OOO
OOOO
OOOOO
OOOOOO
OOOOOOO
OOOOOOOO
Enter the height of a triangle (0 - exit): 9
O
OO
OOO
OOOO
OOOOO
OOOOOO
OOOOOOO
OOOOOOOO
OOOOOOOOO
Enter the height of a triangle (0 - exit): 10
O
OO
OOO
OOOO
OOOOO
OOOOOO
OOOOOOO
OOOOOOOO
OOOOOOOOO
OOOOOOOOOO
Enter the height of a triangle (0 - exit): 0

Answer 3

The simplest way to do this is to use the built in features of the std::iostream:
#include <iostream>
#include <iomanip>
#include <string>
int main()
{
int triHeight;
int c = 0;
std::cout << "Enter the triangle height: \n";
std::cin >> triHeight;
std::cout << std::setfill(' ') << std::right;
for (c = 0; c < triHeight; c++)
{
std::cout << std::setw(triHeight) << std::string(c+1,'0') << '\n';
}
return 0;
}
You can get back to a left aligned triangle by simply changing std::right to std::left.