CODEWITHSUNDEEP
javanested-loops
Clayton
Clayton

Reputation: 73

Generate Alphabetic Pyramid based on user input

I'm having trouble with this homework assignment and would like some assistance. I do not want just solutions, as I want to learn from them.

We are doing a letter pyramid using loops. I can't seem to figure out how to put these FOR loops together to make this work as instructed.

The user should enter a letter (or other character which gives an error) then the program converts the letter to upper case if not already. After the conversion to upper case, loops are used in order to go from the character 'A' to whatever the user enters then back to 'A' again. An example is below.

I have attached my code that I have come up with but the output of the program should be as below but the lines are supposed to be spaces. I just added them for spacing:

Enter a single letter (Enter alphabet to display Pyramid): E

____A
___ABA
__ABCBA
_ABCDCBA
ABCDEDCBA

My output is simply this:

Please enter a single letter:
f
                    ABCDEFEDCBA

Here is the code:

import java.util.*; // For using Scanner class for input

public class LetterPyramid {
    public static void main(String[] args) {
        Scanner key = new Scanner(System.in);
        System.out.println("Please enter a single letter:");
        char input = key.next().charAt(0);
        input = Character.toUpperCase(input);
        if (!(Character.isLetter(input))) {
            System.out.println("Error: Invalid letter: " + input);
        } else {
            for (int i = input; i < 'Z'; i++) {
                System.out.print(" ");
            }
        }
        for (char y = 'A'; y < input; y++) {
            System.out.print(y);
            if (y == input) {
                System.out.println(y);
            }
        }
        for (char x = input; x >= 'A'; x--) {
            System.out.print(x);
        }
        System.out.println();
    }
}

Upvotes: 2

Views: 9795

Answers (4)

marty bu
marty bu

Reputation: 744

Because you said you want to learn sth... here's just an example

For each letter we have to add: we print the word and then add the new letter in the middle of the word. And yes we have to duplicate the letter in the middle. In my example you avoid this by saving the half word instead of saving the whole word.

string word = "A";

for (int i = 'B'; i < input; i++) {
  print word
  print i
  print inverse word
  print newline

  word = word + i
}

probably that is what you wanted...

edit: I frogot to add the space that it's a pyramid: just add print (input - i) spaces before those prints.

Upvotes: 1

nickb
nickb

Reputation: 59699

I stripped down your program to the core algorithm that is at work: Printing the tree.

So, here is what I came up with, along with a demo so you can see it working.

But first, an explanation:

This uses a char variable named middle to keep track of what the current middle character is that we are about to print. This is useful, as we can create the while loop, which states that we should continue to print the tree while the current middle character is less than or equal to the input character.

I also calculate the number of spaces we'll need on the left hand side of the first row with spaces. This is a bit of a trick, so lets look at this line:

int spaces = input - (int) 'A'; // Might be a better way to do w/o cast

We normalize the number of spaces so it ranges from 0 to X, instead of 65 to (X + 65). So, for an input of A, spaces will be 0, which makes sense, since we wouldn't want to print any spaces if the input was just A. If input was B, spaces would be 1, since we'd print one space on the first line.

Then it's just a matter of setting up the loops:

  1. Print the left hand side spaces, which ranges from 0 to spaces
  2. Print the left side of the tree, including the middle, ranging from A to middle
  3. Print the right hand side of the tree, ranging from middle - 1 to A
  4. Print the right side spaces with an identical loop at the first (this is unnecessary, as it won't be visible in the console)

Finally, we print a newline and then need to adjust our flags. So we decrement spaces, since we just printed a line of output, and increment middle, since we want the next line's middle character to be the next character after the one that printed.

Here is the commented code, which I learn better from seeing, so hopefully I've explained it well enough. If you have questions, feel free to ask.

    char middle = 'A'; int spaces = input - (int) 'A';
    while( middle <= input) {

        // Print the left side spaces
        for( int i = 0; i < spaces; i++)
            System.out.print(" ");

        // Print the left side of the tree (including the middle)
        for( char y = 'A'; y <= middle; y++)
            System.out.print( y);

        // Print the right side of the tree
        for( char y = Character.toChars( middle - 1)[0]; y >= 'A'; y--)
            System.out.print( y);

        // Print the right side spaces
        for (int i = 0; i < spaces; i++)
            System.out.print(" ");

        // Print a new line
        System.out.println();

        // Subtract 1 from the number of spaces we need
        spaces--; 

        // Increment the middle character
        middle++;
    }

With an input of F, this will generate:

     A     
    ABA    
   ABCBA   
  ABCDCBA  
 ABCDEDCBA 
ABCDEFEDCBA

Upvotes: 1

Keppil
Keppil

Reputation: 46219

Well, you have managed to build the bottom of the pyramid, so that's a good start. What you need to do next is to put your 3 for loops in a bigger for loop, where you go from 'A' to your input character, and use this as end condition in your smaller loops:

  for(...) {
    for (int i = input; i < 'Z'; i++) {
      System.out.print(" ");
    }
    for (char y = 'A'; y < input; y++) {
      System.out.print(y);
      if (y == input) {
        System.out.println(y);
      }
    }
    for (char x = input; x >= 'A'; x--) {
      System.out.print(x);
    }
  }

Also, the for loop responsible for spaces probably needs some extra work, it doesn't work very well at the moment.

Upvotes: 0

mrswadge
mrswadge

Reputation: 1749

You're really close to what you want. You need to use a loop to adjust your starting point and output from A, then B, C, D, E, F etc.

    if ( ! ( Character.isAlphabetic( input ) ) ) {
      System.out.println( "Error: Invalid letter: " + input );
    } else {
      for ( char n = 'A'; n <= input; n++ ) {
        pyramid( n );
      }
    }

I tried this and it worked for me. I didn't change any code in your loops, just extracted it to a method.

Upvotes: 0

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