Pyramids using asterisks

Question

One of my questions was a problem asked by my prof and that is write a loop that will display the following patterns

I have figured out A but my problem is B the second one

My code for A

 for( row = 10; row >= 0; row--)     // number of rows
         {
            for( cnt = 0; cnt < row; cnt++) // number of stars
               {
                  System.out.print( "*");
               }
               System.out.println();
         }

I have done multiple different ways and have came to the conclusion that A) is going

row(10)1.2.3.4.5.6.7.8.9.10
row(9) 1.2.3.4.5.6.7.8.9
row(8) 1.2.3.4.5.6.7.8

and B) is doing something in the lines of

row(10) 1.2.3.4.5.6.7.8.9.10
row(9)  2.3.4.5.6.7.8.9.10
row(8)  3.4.5.6.7.8.9.10

Can anyone help me with what I am missing in my code to turn it into the mirror image.

Answer 1

The easy way to handle such a problem is to know how many lines you have and base your code on that. The first for loop represents how many lines the pyramid has, in this case, 10. The way to base the number of stars or spaces on the line is the following.

Basically the formula is:

Rate of change*(line) + X = Amount of stars/spaces at that line

Start by getting rate of change, then you get the X and implement it in your code.

In the first line you have 10 stars, then on the second 9 stars, on the third 8 stars, so on and so forth. In order to get rate of change, you subtract the second amount of stars with the first, or the third with the second (you get the same result, since it is decreasing at the same rate). Try 9-10 or 8-9 you get -1. So if you pick the first line, by using the formula you get -1*1 + X = 10, where X will be equal 11. If you would check the "-1*line +11" inside the second for loop, and take line = 1, the answer you get will be 10, which is the amount of stars you have on line 1. You will get the same formula if you take line 2 or 3. Take line 3, you get -1*3 + X = 8 which results in X = 11.

Note that what you use in your code is left hand side of the formula i.e Rate of change*(line) + X

Next you have the number of spaces. I do not know how many spaces you have on the first line, therefore I assumed you have 10 spaces, and incremented by 3. So 10 on the first line, 13 on the second and so on. Again you do the same steps. You need to base your calculations on the amount of lines, first by getting the rate of change by subtracting the amount of spaces on the second line by the first (13- 10). Take line 1. 3*1 + X = 10 (since on the first line we have 10 spaces). X = 7. Try line number 2, 3*2 + X = 13, you still get X = 7. Now you know you have a solid constant formula you can use in your code.

We implement it in the code.

public class Pyramid {
    public static void main (String [] args){
        for(int line = 1; line <=10; line++){
            //j is decreasing since number of stars are decreasing
            for(int j = -1*line + 11; j >=1; j--){
                System.out.print("*");
            }
            //k is decreasing since number of spaces are increasing
            for(int k = line; k <= 3*line +7; k++ ){
                System.out.print(" ");
            }

            for(int j = -1*line + 11; j >=1; j--){
                System.out.print("*");
            }
            //End of line, start new one
            System.out.println();
        }   
    }

Answer 2

public class Printstar {
public static void main(String[] args){
   int space=1;
   for(int i=1;i<=10;i++)
   {
      for(int j=0;j<10-i;j++)
   {
       System.out.print("*");

   }  
      for(int j=0;j<space;j++)
          System.out.print(" ");

      for(int j=0;j<10-i;j++)
          System.out.print("*");
      System.out.println();
      space=space+2;
   }
      }}

Answer 3

This is my ending result for my code based on all the information I have gathered here, thank you all. `

             for( row = 10; row >= 0; row--)   // number of rows
             {
                 for( cnt= 10; cnt - row >= 0; cnt--)   // number of spaces before the asterisk
                 {
                     System.out.print( " ");
                 }
                for( cnt = 0; cnt < row; cnt++) // number of stars
                  {

                     System.out.print("*");
                 }
                System.out.println();
            }


         }

`

Answer 4

Probably shouldn't word your question as asking for homework answers but nonetheless:

public class PyramidPrinter

    public static void printPyramid(boolean mirrorize) {

        for (int i = 10; i > 0; i--) {
            if (mirrorize) {
                for (int j = 10; j > 0; j--) {
                    if (j <= i) {
                        System.out.print("*");
                    } else {
                        System.out.print(" ");
                    }
                }
            } else {
                for (int j = 0; j < 10; j++) {
                    if (i > j) {
                        System.out.print("*");
                    } else {
                        System.out.print(" "); // might not even need
                    }
                }
            }
            System.out.println();
        }

    }

    public static void main(String[] args) {
        printPyramid(false); // A
        printPyramid(true);  // B
    }
}

The key here is use of a combination of forward and backward incrementing for-loops, to essentially pad spaces with asterisks and pad asterisks with spaces.

Results:

**********
********* 
********  
*******   
******    
*****     
****      
***       
**        
*         
**********
 *********
  ********
   *******
    ******
     *****
      ****
       ***
        **
         *

Answer 5

Here is a complete code -

int main(){

    char star = '*';
    char space = ' ';
    int noOfTimesToPrint = 10;
    int noOfSpaceToPrint = 1;
    int line = 0;
    int starCount = 0;
    int spaceCount = 1;

    for(line=1; line<=10; line++){

     for(starCount=1; starCount<=noOfTimesToPrint; starCount++){
        printf("%c", star);
     }

     for(spaceCount=1; spaceCount<=noOfSpaceToPrint; spaceCount++){
        printf("%c", space);
     }
     noOfSpaceToPrint = noOfSpaceToPrint+2 ;

     for(starCount=1; starCount<=noOfTimesToPrint; starCount++){
        printf("%c", star);
     }
     printf("\n");
     --noOfTimesToPrint;
    }
}  

Some explanations -

• You can adjust the initial no of space to print by setting noOfSpaceToPrint. Here it is set for printing 1 space. You can adjust according to your requirement.
• The first inner for loop block print the A portion of your image
• The second inner for loop block print the space portion of your image and
• The last inner for loop portion print the B portion of your image
• The outer for loop portion is used to print a line that is -

line 1 : ********** **********

and so on

Hope It will help. Thanks a lot

Output of the code is :

Answer 6

There you go ! I put everything into a class for you so that you can run the program directly..

I am not implementing it very efficiently probably.

As you can see I am printing spaces which start from 10, and for every line I add 2 more spaces in order to mirror the "asterisk" effect

public class asterisk {
    public static void main(String[] args) {
        int spaces=10;
         for( int row = 10; row >= 0; row--)     // number of rows
         {
            for( int cnt = 0; cnt < row; cnt++) // number of stars
               {
                  System.out.print( "*");
               }
               for( int cnt = 0; cnt < spaces; cnt++) {
               System.out.print( " "); }
               spaces=spaces+2;
                for( int cnt = 0; cnt < row; cnt++) {
               System.out.print( "*"); }

               System.out.println();
         }
    }
}

If you want more or less than 10 spaces between A and B you just change the initial value that you set the variable "spaces" to !

Answer 7

You want to try something like this:

for( int row = 10; row >= 0; row--)     // number of rows
     {
        for( int cnt = 10; cnt - row >= 0; cnt--) // number of stars
           System.out.print(" ");
        for (int cnt = 0; cnt <= row; cnt++)
            System.out.print( "*");

        System.out.println();
     }

Hope that helps.

Answer 8

look into String.format() where you can pad (left or right) any string to a certain width like so:

String stars = //use your loop from (a) to produce a number of stars
String toOutput = String.format("%10s", stars);