[java] Printing *s as triangles in Java?

My assignment in my Java course is to make 3 triangles. One left aligned, one right aligned, and one centered. I have to make a menu for what type of triangle and then input how many rows is wanted. The triangles have to look like this

*
**
***
****


   *
  **
 ***
****


  *
 ***
*****

So far I was able to do the left aligned triangle but I can't seem to get the other two. I tried googling but nothing turned up. Can anyone help? I have this so far.

import java.util.*;
public class Prog673A
{
    public static void leftTriangle()
    {
        Scanner input = new Scanner (System.in);
        System.out.print("How many rows: ");
        int rows = input.nextInt();
        for (int x = 1; x <= rows; x++)
        {
            for (int i = 1; i <= x; i++)
            {
                System.out.print("*");
            }
            System.out.println("");
        }
    }
    public static void rightTriangle()
    {
        Scanner input = new Scanner (System.in);
        System.out.print("How many rows: ");
        int rows = input.nextInt();
        for (int x = 1; x <= rows; x++)
        {
            for (int i = 1; i >= x; i--)
            {
                System.out.print(" ");
            }
            System.out.println("*");
        }
    }
    public static void centerTriangle()
    {

    }
    public static void main (String args [])
    {
        Scanner input = new Scanner (System.in);
        System.out.println("Types of Triangles");
        System.out.println("\t1. Left");
        System.out.println("\t2. Right");
        System.out.println("\t3. Center");
        System.out.print("Enter a number: ");
        int menu = input.nextInt();
        if (menu == 1)
            leftTriangle();
        if (menu == 2)
            rightTriangle();
        if (menu == 3)
            centerTriangle();
    }
}

Sample Output:

Types of Triangles
1.  Left
2.  Right
3.  Center
Enter a number (1-3):  3
How many rows?: 6

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

This question is related to java loops

The answer is


import java.util.Scanner;

public class A {

    public void triagle_center(int max){//max means maximum star having
        int n=max/2;
        for(int m=0;m<((2*n)-1);m++){//for upper star
            System.out.print(" ");
        }
        System.out.println("*");

        for(int j=1;j<=n;j++){
            for(int i=1;i<=n-j; i++){
                System.out.print("  ");
            }
            for(int k=1;k<=2*j;k++){
            System.out.print("* ");
            }

            System.out.println();
        }


    }

    public void triagle_right(int max){
        for(int j=1;j<=max;j++){
            for(int i=1;i<=j; i++){
                System.out.print("* ");
            }

            System.out.println();
        }
    }

    public void triagle_left(int max){
        for(int j=1;j<=max;j++){
            for(int i=1;i<=max-j; i++){
                System.out.print("  ");
            }
            for(int k=1;k<=j; k++){
                System.out.print("* ");
            }

            System.out.println();
        }
    }

    public static void main(String args[]){
        A a=new A();
        Scanner input = new Scanner (System.in);
        System.out.println("Types of Triangles");
        System.out.println("\t1. Left");
        System.out.println("\t2. Right");
        System.out.println("\t3. Center");
        System.out.print("Enter a number: ");
        int menu = input.nextInt();
        Scanner input1 = new Scanner (System.in);
        System.out.print("maximum Stars in last row: ");
        int row = input1.nextInt();
        if (menu == 1)
            a.triagle_left(row);
        if (menu == 2)
            a.triagle_right(row);
        if (menu == 3)
            a.triagle_center(row);
    }
}

// This is for normal triangle

for (int i = 0; i < 5; i++)
        {
            for (int j = 5; j > i; j--)
            {
                System.out.print(" ");
            }
            for (int k = 1; k <= i + 1; k++) {
                System.out.print(" *");
            }
            System.out.print("\n");
        }

// This is for left triangle, just removed space before printing *

for (int i = 0; i < 5; i++)
        {
            for (int j = 5; j > i; j--)
            {
                System.out.print(" ");
            }
            for (int k = 1; k <= i + 1; k++) {
                System.out.print("*");
            }
            System.out.print("\n");
        }

For left aligned right angle triangle you could try out this simple code in java:

import java.io.*;
import java.util.*;

public class Solution {

    public static void main(String[] args) {
      Scanner sc=new Scanner(System.in);
      int size=sc.nextInt();
       for(int i=0;i<size;i++){
           for(int k=1;k<size-i;k++){
                   System.out.print(" ");
               }
           for(int j=size;j>=size-i;j--){

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

Question:

      *
     ***
    *****

Answer:

    int i,a,j;
    i=5;
    while (i>=3)
    {
        a=1;
        while (a<=i)
        {

            System.out.print(" ");
            a++;
        }
        j=10;
        while (j/2>=i)
        {
            System.out.print("*");
            --j;
        }
        System.out.println("");
        i--;
    }   

Enjoy!!


well for the triangle , you need to have three loops in place of two , one outer loop to iterate the no of line two parallel loops inside the main loop first loop prints decreasing no of loops second loop prints increasing no of '' well i could give the exact logic as well , but its better if you try first just concentrate how many spaces and how many '' u need in every line relate the no of symbols with loop iterating no of lines and you're done ..... if it bothers more , let me know , i'll explain with logic and code as well


Ilmari Karonen has good advice, and I'd just like to generalize it a bit. In general, before you ask "how can I get a computer to do this?" ask "how would I do this?"

So, if someone gave you an empty Word document and asked you to create the triangles, how would you go about doing it? Whatever solution you come up with, it's usually not hard to translate it to Java (or any other programming language). It might not be the best solution, but (hopefully!) it'll work, and it may point you to a better solution.

So for instance, maybe you would say that you'd type out the base, then go up a line, then type the next highest line, etc. That suggests that you can do the same in Java -- create a list of Strings, base-to-top, and then reverse them. That might suggest that you can just create them in reverse order, and then not have to reverse them. And then that might suggest that you don't need the list anymore, since you'll just be creating and printing them out in the same order -- at which point you've come up with essentially Ilmari Karonen's advice.

Or, maybe you'd come up with another way of doing it -- maybe you'd come up with Ilmari Karonen's idea more directly. Regardless, it should help you solve this and many other problems.


Left alinged triangle- * **



from above pattern we come to know that-
1)we need to print pattern containing n rows (for above pattern n is 4).
2)each  row contains star and no of stars i each row is incremented by 1.
So for Left alinged triangle we need to use 2 for loop.
1st "for loop" for printing n row.
2nd  "for loop for printing stars in each rows. 


 Code for  Left alinged triangle-

 public static void leftTriangle()
{
       /// here  no of rows is 4
 for (int a=1;a<=4;a++)// for loop for row
 {   
 for (int b=1;b<=a;b++)for loop for column
 {
 System.out.print("*");
 }

System.out.println();}
}

Right alinged triangle- *
**



from above pattern we come to know that-
1)we need to print pattern containing n rows (for above pattern n is 4).
 2)In each  row we need to print spaces followed by a star & no of spaces            in each row is decremented by 1.
 So for Right alinged triangle we need to use 3 for loop.
 1st "for loop" for printing n row.
 2nd  "for loop for printing spaces.
 3rd "for loop" for printing stars.

Code for Right alinged triangle -

public void rightTriangle()
{
    // here 1st print space and then print star
  for (int a=1;a<=4;a++)// for loop for row
 { 
 for (int c =3;c>=a;c--)// for loop fr space
 {  
 System.out.print(" ");
 }
 for (int d=1;d<=a;d++)// for loop for column
 { 
 System.out.print("*");   
 }
 System.out.println(); 
 }
 }

Center Triangle- *
* *



from above pattern we come to know that- 1)we need to print pattern containing n rows (for above pattern n is 4). 2)Intially in each row we need to print spaces followed by a star & then again a space . NO of spaces in each row at start is decremented by 1. So for Right alinged triangle we need to use 3 for loop. 1st "for loop" for printing n row. 2nd "for loop for printing spaces. 3rd "for loop" for printing stars.

Code for center Triangle-

public  void centerTriangle()
{   
for (int a=1;a<=4;a++)// for lop for row
{   
for (int c =4;c>=a;c--)// for loop for space
{  
System.out.print(" ");
}
for (int b=1;b<=a;b++)// for loop for column
{
System.out.print("*"+" ");
}
System.out.println();}
}

CODE FOR PRINTING ALL 3 PATTERNS - public class space4 { public static void leftTriangle() { /// here no of rows is 4 for (int a=1;a<=4;a++)// for loop for row {
for (int b=1;b<=a;b++)for loop for column { System.out.print("*"); }

System.out.println();}
}

public static void rightTriangle()
{
    // here 1st print space and then print star
  for (int a=1;a<=4;a++)// for loop for row
 { 
 for (int c =3;c>=a;c--)// for loop for space
 {  
 System.out.print(" ");
 }
 for (int d=1;d<=a;d++)// for loop for column
 { 
 System.out.print("*");   
 }
 System.out.println(); 
 }
 }

public static void centerTriangle()
{   
for (int a=1;a<=4;a++)// for lop for row
{   
for (int c =4;c>=a;c--)// for loop for space
{  
System.out.print(" ");
}
for (int b=1;b<=a;b++)// for loop for column
{
System.out.print("*"+" ");
}
System.out.println();}
}
public static void main (String args [])
{
space4 s=new space4();
s.leftTriangle();
s.rightTriangle();
s.centerTriangle();
}
}

1) Normal triangle

package test1;


 class Test1 {

     public static void main(String args[])
     {
         int n=5;
     for(int i=0;i<n;i++)
     {

         for(int j=0;j<=n-i;j++)
         {

             System.out.print(" ");
         }

         for(int k=0;k<=2*i;k++)
         {
         System.out.print("*");
         }

         System.out.println("\n");

     }

     }

2) right angle triangle

package test1;


 class Test1 {

     public static void main(String args[])
     {
         int n=5;
     for(int i=0;i<n;i++)
     {

         for(int j=0;j<=n-i;j++)
         {

             System.out.print(" ");
         }

         for(int k=0;k<=i;k++)
         {
         System.out.print("*");
         }

         System.out.println("\n");

     }

     }


}

     }

3) Left angle triangle

package test1;


 class Test1 {

     public static void main(String args[])
     {
         int n=5;
     for(int i=0;i<n;i++)
     {

         for(int j=0;j<=i;j++)
         {

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

         System.out.println("\n");

     }

     }


}

package apple;

public class Triangle
{
private static final int row = 3;

public static void main(String...strings){
    printLeftTrangle();
    System.out.println();
    printRightTrangle();
    System.out.println();
    printTrangle();
}

/*  Pattern will be
     *
     **
     ***
     ****
 */

public static void printLeftTrangle(){

    for(int y=1;y<=row;y++){
     for(int x=1;x<=y;x++)
         System.out.print("*");
     System.out.println();
    }
}

/*  Pattern will be
        *
       **
      ***
     ****
 */
public static void printRightTrangle(){
    for(int y=1;y<=row;y++){
        for(int space=row;space>y;space--)
            System.out.print(" ");
        for(int x=1;x<=y;x++)
            System.out.print("*");
        System.out.println();
    }
}

/*  Pattern will be
     *
    ***
   *****
*/

public static void printTrangle(){

    for(int y=1, star=1;y<=row;y++,star +=2){
        for(int space=row;space>y;space--)
            System.out.print(" ");
        for(int x=1;x<=star;x++)
            System.out.print("*");
        System.out.println();
    }
}
}

This is the least complex program, which takes only 1 for loop to print the triangle. This works only for the center triangle, but small tweaking would make it work for other's as well -

import java.io.DataInputStream;

public class Triangle {
    public static void main(String a[]) throws Exception{
        DataInputStream in = new DataInputStream(System.in);

        int n = Integer.parseInt(in.readLine());
        String b = new String(new char[n]).replaceAll("\0", " ");
        String s = "*";
        for(int i=1; i<=n; i++){
            System.out.print(b);
            System.out.println(s);
            s += "**";
            b = b.substring(0, n-i);
            System.out.println();
        }
    }
}

You might be interested in this too

      Scanner sc = new Scanner(System.in);
      int n=sc.nextInt();
      int b=0;
      for(int i=n;i>=1;i--){
      if(i!=n){
      for(int k=1;k<=b;k++){
      System.out.print(" ");
        }
            }
       for(int j=i;j>=1;j--){
       System.out.print("*");
       if(i!=1){
       System.out.print(" ");
        }
            }
       System.out.println();
       b=b+2;
        }

Output:: 5

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

public class triangle {
    public static void main ( String arg[] ){

        System.out.print("Enter Triangle Size : ");
        int num=0;
        try{
            num=Integer.parseInt( read.readLine() );
        } catch(Exception Number){
            System.out.println("Invalid Number!");
        }
            for(int i=1;i<=num;i++){
                for(int j=1;j<num-(i-1);j++){
                    System.out.print(" ");
                }
                for(int k=1;k<=i;k++){
                    System.out.print("*");
                    for(int k1=1;k1<k;k1+=k){

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

Find the following , it will help you to print the complete triangle.

package com.raju.arrays;

public class CompleteTriange {

public static void main(String[] args) {
    int nuberOfRows = 10;
      for(int row = 0; row<nuberOfRows;row++){

          for(int leftspace =0;leftspace<(nuberOfRows-row);leftspace++){
              System.out.print(" ");
          }
          for(int star = 0;star<2*row+1;star++){
              System.out.print("*");
          }
          for(int rightSpace =0;rightSpace<(nuberOfRows-row);rightSpace++){
              System.out.print(" ");
          }
          System.out.println("");
      }

}

}

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




I know this is pretty late but I want to share my solution.

public static void main(String[] args) {
    String whatToPrint = "aword";
    int strLen = whatToPrint.length(); //var used for auto adjusting the padding
    int floors = 8;
    for (int f = 1, h = strLen * floors; f < floors * 2; f += 2, h -= strLen) {
        for (int k = 1; k < h; k++) {
                System.out.print(" ");//padding
            }
        for (int g = 0; g < f; g++) {
            System.out.print(whatToPrint);
        }
        System.out.println();
    }
}

The spaces on the left of the triangle will automatically adjust itself depending on what character or what word you want to print.

if whatToPrint = "x" and floors = 3 it will print

x xxx xxxxx If there's no automatic adjustment of the spaces, it will look like this (whatToPrint = "xxx" same floor count)

xxx xxxxxxxxx xxxxxxxxxxxxxxx

So I made add a simple code so that it will not happen.

For left half triangle, just change strLen * floors to strLen * (floors * 2) and the f +=2 to f++.

For right half triangle, just remove this loop for (int k = 1; k < h; k++) or change h to 0, if you choose to remove it, don't delete the System.out.print(" ");.


public static void main(String[] args) {

    System.out.print("Enter the number: ");
    Scanner userInput = new Scanner(System.in);
    int myNum = userInput.nextInt();
    userInput.close();

    System.out.println("Centered Triange");
    for (int i = 1; i <= myNum; i+=1) {//This tells how many lines to print (height)

        for (int k = 0; k < (myNum-i); k+=1) {//Prints spaces before the '*'
            System.out.print(" ");
        }

        for (int j = 0; j < i; j++) { //Prints a " " followed by '*'.   
            System.out.print(" *");
        }

        System.out.println(""); //Next Line     
    }

    System.out.println("Left Triange");
    for (int i = 1; i <= myNum; i+=1) {//This tells how many lines to print (height)

        for (int j = 0; j < i; j++) { //Prints the '*' first in each line then spaces.  
            System.out.print("* ");
        }

        System.out.println(""); //Next Line         
    }

    System.out.println("Right Triange");
    for (int i = 1; i <= myNum; i+=1) {//This tells how many lines to print (height)

        for (int k = 0; k < (myNum-i); k+=1) {//Prints spaces before the '*'
            System.out.print("  ");
        }

        for (int j = 0; j < i; j+=1) { //Prints the " " first in each line then a "*".  
            System.out.print(" *");
        }

        System.out.println(""); //Next Line         
    }

}

For the right triangle, for each row :

  • First: You need to print spaces from 0 to rowNumber - 1 - i.
  • Second: You need to print \* from rowNumber - 1 - i to rowNumber.

Note: i is the row index from 0 to rowNumber and rowNumber is number of rows.

For the centre triangle: it looks like "right triangle" plus adding \* according to the row index (for ex : in first row you will add nothing because the index is 0 , in the second row you will add one ' * ', and so on).


For center triangle

      Scanner sc = new Scanner(System.in);
      int n=sc.nextInt();
      int b=(n-1)*2;  
      for(int i=1;i<=n;i++){
      int t= i;
      for(int k=1;k<=b;k++){
      System.out.print(" ");
       }
       if(i!=1){
        t=i*2-1;
       }
       for(int j=1;j<=t;j++){
       System.out.print("*");
       if(j!=t){
       System.out.print(" ");
       }
        }
        System.out.println();
            b=b-2;  
        }

output:

            *
          * * *

(a)   (b)        (c)   (d)
* ********** ********** *
** ********* ********* **
*** ******** ******** ***
**** ******* ******* ****
***** ****** ****** *****
****** ***** ***** ******
******* **** **** *******
******** *** *** ********
********* ** ** *********
********** * * **********

int line;
int star;
System.out.println("Triangle a");
        for( line = 1; line <= 10; line++ )
        {
            for( star = 1; star <= line; star++ )
            {

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

 System.out.println("Triangle b");

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

        if(line<star)
                System.out.print( "*" );
                else
                  System.out.print(" ");
            }
            System.out.println();
        }

 System.out.println("Triangle c");

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

        if(line<=star)
                System.out.print( "*" );
                //else
                 // System.out.print(" ");
            }
            System.out.println();
        }

 System.out.println("Triangle d");

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

        if(line>10-star)
                System.out.print( "*" );
                else
                  System.out.print(" ");
            }
            System.out.println();
        }

    for(int i=1;i<=5;i++)
    {
        for(int j=5;j>=i;j--)
        {
            System.out.print(" ");
        }
        for(int j=1;j<=i;j++)
        {
            System.out.print("*");
        }

        for(int j=1;j<=i-1;j++)
        {
            System.out.print("*");
        }
        System.out.println("");
    }

 *
***




This will print stars in triangle:

`   
public class printstar{
public static void main (String args[]){
int m = 0;
for(int i=1;i<=4;i++){
for(int j=1;j<=4-i;j++){
System.out.print("");}

for (int n=0;n<=i+m;n++){
if (n%2==0){
System.out.print("*");}
else {System.out.print(" ");}
}
m = m+1;
System.out.println("");
}
}
}'

Reading and understanding this should help you with designing the logic next time..