printing a triangle

i have this problem : take a number from the user, and print a triangle with that number of rows. everything is clear except for the loop that does the actual printing, i just can't come up with anything.

number: 3

....*
..***
*****

(i used dots instead of spaces in my post)

Post code please...

Asterisk triangles are boring. Give your teacher something with a little more pizzaz!

Code:

---

#include <stdio.h>
#include <stdlib.h>

int main ( void )
{
  char buff[BUFSIZ];
  int height;
  int spaces;
  int i, j;

  printf ( "Enter the height (32 is a good one): " );
  fflush ( stdout );
  if ( fgets ( buff, sizeof buff, stdin ) == NULL ) {
    fprintf ( stderr, "Error reading input\n" );
    return EXIT_FAILURE;
  }
  if ( sscanf ( buff, "%d", &height ) != 1 ) {
    fprintf ( stderr, "Invalid input detected\n" );
    return EXIT_FAILURE;
  }
  spaces = height / 2;
  for ( i = 0; i < height; i += 2, spaces-- ) {
    for ( j = 0; j < spaces; j++ )
      putchar ( ' ' );
    for ( j = 0; j <= i; j++ )
      putchar ( ( ~i & j ) ? ' ' : '*' );
    putchar ( '\n' );
  }

  return EXIT_SUCCESS;
}

---

Code:

---

(defun pramt(c a)
        (unless (= a 0)
        (princ c)
        (pramt c (- a 1))))

(defun lines(amt max)
        (unless (= amt (+ max 1)) (pramt " " (- max amt))
        (pramt "*" (+ 1 (* (- amt 1) 2)))
        (terpri)
        (lines (+ amt 1) max)))

---

My code owns yours, prelude. Eat lisp!

Code:

---

usage: (lines 1 5)
output:
    *
    ***
  *****
  *******
 *********

---

If you do want asterisks:

Code:

---

#include <stdio.h>
#include <stdlib.h>

int main()
{
        int Rows = 0;
        int Row_Width = 1;

        printf("%s", "Enter Number of Rows\n");
        scanf("%d", &Rows);
       
        int Num_Rows = Rows-1;

        for(int i = 0; i < Rows; i++)
        {     
                for(int k = Num_Rows; k > 0; k--)
                        {
                                printf("%s", " ");
                        }
                        Num_Rows --;

                for(int j = 0; j < Row_Width; j++)
                {
                        printf("%s", "*");                       
                }

                printf("\n");       
                Row_Width += 2;
                               
        }

        return EXIT_SUCCESS;
}

---

Piece of crap compared to the one above. :eek:

>My code owns yours, prelude. Eat lisp!
Did you run my code? :p Anyway, what are you doing posting lisp on a C board? :rolleyes:

> Did you run my code?

Woah, that is cool.

> Anyway, what are you doing posting lisp on a C board? :rolleyes:

I'm trying to learn it. :(

Quote:

---

Originally posted by Prelude
Did you run my code?

---

Prelude, you are a Goddess! And very weird... :D

Once again predlude showes us how ungodly good she is:)

Quote:

---

Originally posted by Brian2

Code:

---

(defun pramt(c a)
        (unless (= a 0)
        (princ c)
        (pramt c (- a 1))))

(defun lines(amt max)
        (unless (= amt (+ max 1)) (pramt " " (- max amt))
        (pramt "*" (+ 1 (* (- amt 1) 2)))
        (terpri)
        (lines (+ amt 1) max)))

---

---

In C it would look like this:

Code:

---

void lines(int rows) {
    for(i=0; i<rows; i++) {
        for(j=0; j<rows-i-1; j++) printf(" ");
        for(k=0; k<i*2+1; k++) printf("*");
        printf("\n");
    }
}

---

I think the C solution is shorter and better readable.

Quote:

---

Originally posted by Prelude

Code:

---

      putchar ( ( ~i & j ) ? ' ' : '*' );

---

---

Nice. Can you explain how it works?

Code:

---

(defun stars (amt)
        (dotimes (cur amt) (dotimes (num (- amt cur)) (princ " "))
        (dotimes (num (1+ (* (1- cur) 2))) (princ "*")) (terpri)))

---

HA! (oh and you didnt declare some of your variables). Also, code is not supposed to be readable. That's why they call it "code"! :)

>Nice. Can you explain how it works?
Sure, but that would take all the fun out of figuring it out for yourself. :) But I'll give you a big hint. For each iteration of the outer loop, print the amount of spaces and then print i + 1 of i's binary digits. Like so:

Code:

---

void printbin ( unsigned bin )
{
  int i;

  for ( i = 0; i <= bin; i++ )
    printf ( "%d", !!( bin & i ) );
  printf ( "\n" );
}

...

spaces = height / 2;
for ( i = 0; i < height; i += 2, spaces-- ) {
  for ( j = 0; j < spaces; j++ )
    putchar ( ' ' );
  printbin ( i );
}

---

Be sure to notice the pattern from the bottom up, then try complimenting bin inside of the loop to rotate the pattern 180 degrees:

Code:

---

printf ( "%d", !!( ~bin & i ) );

---

thank you all for the replies and your solutions. Prelude's code is great, although i don't understand the last part. Ohh well , i'll just read it a few more times...