Develop Reference

Using nested For Loops to create a table of numbers and stars

I need to print a table that looks like this if the user entered a 5 using nested for loops:
****5
***45
**345
*2345
12345
I've been working on this for hours and the closest I got was:
int size = scan.nextInt();
for (int i = 1; i <= size; i++)
{
for (int star = size-1; star >= i; star--)
System.out.print("*");
for (int k = 1; k <= i; k++)
System.out.print(i);
System.out.println();
}
Which outputs this:
****1
***12
**123
*1234
12345

You have too many loops; I find it easier to reason about zero based looping so I'm going to use that. Iterate i and j from 0 to size. If j + 1 is greater than size - i - 1 then we want to print j + 1. Otherwise, we want a star. Like,
for (int i = 0; i < size; i++) {
for (int j = 0; j < size; j++) {
if (j + 1 > size - i - 1) {
System.out.print(j + 1);
} else {
System.out.print('*');
}
}
System.out.println();
}
For size = 5 that outputs (as requested)
****5
***45
**345
*2345
12345
If you simply must have one based indices, that would be
for (int i = 1; i <= size; i++) {
for (int j = 1; j <= size; j++) {
if (j > size - i) {
System.out.print(j);
} else {
System.out.print('*');
}
}
System.out.println();
}

If you want to keep your loops and avoid if statements, you can tweak last loop by changing
for (int k = 1; k <= i; k++)
into
for (int k = 1+size-i; k <= size; k++)
Btw I also find it way easier to start loops from 0, so updated code would look like this:
int size = scan.nextInt();
for (int i = 0; i < size; i++)
{
for (int star = size-1; star > i; star--)
System.out.print("*");
for (int k = size-i; k <= size; k++)
System.out.print(k);
System.out.println();
}
I hope it helps

replace every second line of my triangle with a blank line for loops

instead of getting a full triangle with 5 lines of "*" how do I replace every second line with a blank line, e.g. to look like this
5
555
55555
This is my code:
for(int i = 0; i < 5; i++) {
for(int j = i; j < 5; j++) {
System.out.print(" ");
}
for(int k = 0; k <= (i*2); k++) {
System.out.print("5");
}
System.out.println();
}

you need small modification in your code and you can get what you want.
for(int i = 0; i < 5; i++) {
for(int j = i; j < 5; j++) {
System.out.print(" ");
}
for(int k = 0; k <= (i*2); k++) {
if(i%2==0)
System.out.print("*");
}
System.out.println();
}
check it out.

Just test for i % 2
for(int i = 0; i < 5; i++) {
for(int j = i; j < 5; j++) {
System.out.print(" ");
}
for(int k = 0; k <= (i*2); k++) {
System.out.print(i % 2 == 0 ? "*" : " ");
}
System.out.println();
}
edit
If you want to print 5 instead or * then modify the code to use 5

Check this:
int num= 5; // 'num' denotes the number of lines
int numOfSpaces;
for(int i = 1; i <= num; i++) {
if( i%2 != 0) // checks whether the line number is odd. If odd, prints '*'
{
numOfSpaces = (num-i) / 2; // find the number of blank spaces
for(int j = 1; j <= numOfSpaces; j++) {
System.out.print(" ");
}
for(int k = 1; k <= i; k++) { // number of '*'s to be printed = current line number = i
System.out.print("*");
}
System.out.println();
}
else{
System.out.println(); // leaves every second line blank (ie.,if line number is even.)
}
}

//try this code. It may help you to achieve your output
[Check screen shot for the output of the below code][1]
for (int i = 0; i < 5; i++)
{
for (int j = 0; j < 5 - i; j++)
{
System.out.print(" ");
}
for (int k = 0; k <= i; k++)
{
if(i%2!=0)
{
System.out.print(" ");
}
else{
System.out.print("* ");
}
}
System.out.println();
}

The Code below is Working now.
A simple if condition will solve your problem. Just check if the
value of i is divisible by 2. If it is true then print a
blank line. Else Print * and you are done!
* will be printed on 1st, 3rd and 5th lines.
Blank Space will be printed on 2nd and 4th lines.
public class PrintPattern{
public static void main(String []args){
int lineNo=0; // New Variable for Line Number (Can Use variable 'i' also)
for(int i = 0; i < 5; i++) {
lineNo++;
for(int j = i; j < 5; j++) {
System.out.print(" ");
}
if(lineNo%2!=0){
for(int k = 0; k <= (i*2); k++)
System.out.print('*'); // Will print '*' (or '5') Sequence for Odd Lines - 1st, 3rd, 5th Lines
System.out.println();
}
else
System.out.println();// Will print Blank Line for Even Lines - 2nd and 4th Lines
}
}
}

Try this
for(int i = 0; i < 5; i++) {
for(int j = i; j < 5; j++) {
System.out.print(" ");
}
for(int k = 0; k <= (i*2); k++) {
System.out.print("5"); //Use 5 instaed of * to draw
}
System.out.println();
System.out.println(); //This one will solve your problem
}
Output will be:
5
555
55555
5555555
555555555

I think that you can just enter one more print statement inside the loop:
for(int i = 0; i < 5; i++) {
System.out.println();
for(int j = i; j < 5; j++) {
System.out.print(" ");
}
for(int k = 0; k <= (i*2); k++) {
System.out.print("*");
}
System.out.println();
}
Output
*
***
*****
*******
*********

Height of Java Diamond Asterisk

How can i get this code to display the height correctly? So if the width of the diamond asterisk is 3, and the height is 5, then the diamond will look like this.
*
***
***
***
*
It just adds any excess height to the middle. Here is my code so far. It can do the width just fine.
public static void main(String[] args) {
int width, height, heightT;
Scanner scan = new Scanner(System.in);
while(true) {
System.out.println("Enter width of diamond (odd number between 0-19): ");
width = scan.nextInt();
if (width % 2 != 0) {
if (0 <= width && width <= 19) {
break;
}
}
}
while(true) {
System.out.println("Enter height of diamond (greater than or equal to width): ");
height = scan.nextInt();
if(height >= width) {
heightT = height - width;
break;
}
}
for(int i = 1; i < width + 1; i += 2) {
for(int j = 0; j < 9 - i / 2; j++)
System.out.print(" ");
for(int j = 0; j < i; j++)
System.out.print("*");
System.out.print("\n");
}
for(int i = width - 2; i > 0; i -= 2) {
for(int j = 0; j < 9 - i / 2; j++)
System.out.print(" ");
for(int j = 0; j < i; j++)
System.out.print("*");
System.out.print("\n");
}
}

When solving this type of logic you have to always look at the things that you know never change. In this case, 3 things never change:
1. The first line. Always equal to one asterisk.
2. The middle line. Always equal to width in asterisks.
3. The last line. Always equal to one asterisk.
Now, split the diamond in two by the middle row. Notice the total height will always be the height of the top part (or bottom) times 2 plus 1 (the middle row). You get something more less like this:
for(int i = 0; ((i*2)+1) <= height; i++){
//Print top
}
// Print middle row outside of loops or inside if you must.
for(int i = 0; ((i*2)+1) <= height; i++){
//Print bottom.
}
EDIT: This would only be true for diamonds where height is greater than or equal to the width.
EDIT: This code solves your problem (given height is greater than or equal to width). However, it does not handle width = 0 or width = 1 properly. I trust that would be trivial enough for you to do.
public static void main(String[] args) {
int height = 9, width = 9;
int spaces = (width - 1) / 2, asterisks = 1;
for(int i = 0;((i*2)) < height; i++){
for(int ii = 0;ii < spaces;ii++){
System.out.print(" ");
}
for(int ii = 0;ii < asterisks;ii++){
System.out.print("*");
}
spaces--;
if(asterisks < width)asterisks += 2;
System.out.println();
}
spaces = 0;
for(int i = 0; ((i*2)+1) < height; i++){
if(width < height){
for(int ii = 0;ii < spaces;ii++){
System.out.print(" ");
}
for(int ii = 0;ii < asterisks;ii++){
System.out.print("*");
}
}else{
for(int ii = 0;ii < (spaces + 1);ii++){
System.out.print(" ");
}
for(int ii = 0;ii < (asterisks - 2);ii++){
System.out.print("*");
}
}
spaces++;
asterisks -= 2;
System.out.println();
}
}

You can calculate the difference between height and width and reuse your logic in a while loop.
for(int i = 1; i < width + 1; i += 2) {
for(int j = 0; j < 9 - i / 2; j++)
System.out.print(" ");
for(int j = 0; j < i; j++)
System.out.print("*");
System.out.print("\n");
}
int dif = height-width;
while(dif !=0){
for(int i = width; i < width + 1; i += 2) {
for(int j = 0; j < 9 - i / 2; j++)
System.out.print(" ");
for(int j = 0; j < i; j++)
System.out.print("*");
System.out.print("\n");
}
dif--;
}
for(int i = width - 2; i > 0; i -= 2) {
for(int j = 0; j < 9 - i / 2; j++)
System.out.print(" ");
for(int j = 0; j < i; j++)
System.out.print("*");
System.out.print("\n");
}

Asterisk in Nested loops, Java

I am trying to make my code print out the Asterisk in the image, you see below. The Asterisk are align to the right and they have blank spaces under them. I can't figure out, how to make it go to the right. Here is my code:
public class Assn4 {
public static void main(String[] args) {
for (int i = 0; i <= 3; i++) {
for (int j = 0; j <= i; j++) {
System.out.print("*");
}
for (int x = 0; x <= 1; x++) {
System.out.println(" ");
}
for (int j = 0; j <= i; j++) {
System.out.print("*");
}
}
System.out.println();
}
}

Matrix problems are really helpful to understand loops..
Understanding of your problem:
1) First, printing star at the end- That means your first loop should be in decreasing order
for(int i =7;i>=0; i+=i-2)
2) Printing star in increasing order- That means your second loop should be in increasing order
for(int j =0;j<=7; j++)
Complete code:
for(int i =7;i>=0; i=i-2){ // i=i-2 because *s are getting incremented by 2
for(int j =0;j<=7; j++){
if(j>=i){ // if j >= i then print * else space(" ")
System.out.print("*");
}
else{
System.out.print(" ");
}
}
System.out.println();// a new line just after printing *s
}

Starting loops with 1 can sometimes help you visualize better.
int stopAt = 7;
for (int i = 1; i <= stopAt ; i += 2) {
for (int j = 1; j <= stopAt; j++) {
System.out.print(j <= stopAt - i ? " " : "*");
}
System.out.println();
}
Notice, how each row prints an odd number of *s ending at the line with 7. So, you start with i at 1 and go through 3 1+2, 5 3+2, and then stopAt 7 5+2.
The nested for loop has to print 7 characters always to make sure *s appear right aligned. So, the loop runs from 1 to 7.

Here the complete code:
for(int i = 0; i < 8; i++){
if( i%2 != 0){
for(int x = 0; x < i; x++){
System.out.print("*");
}
}else{
System.out.println();
}
}

Looping Algorithm

How do I make this:
*******
-*****-
--***--
---*---
--***--
-*****-
*******
The following is my code that I have written to try to accomplish the above, but it is not working as expected:
public static void stars(/*int jmlBaris*/) {
for ( int i = 7; i >= 1; i-=2) {
for (int j = 1; j <= i; j++) {
System.out.print("*");
}
System.out.println("");
}
for (int i = 1; i <= 7; i+=2) {
for (int j = 1; j <= i; j++){
System.out.print("*");
}
System.out.println("");
}
}
public static void main(String[] args) {
stars();
}
}

This is how I might write it.
// three loops
public static void stars(int size) {
for (int y = 0; y < size; y++) {
for (int i = 0; i < y && i < size - y - 1; i++)
System.out.print(' ');
for (int i = Math.min(y, size - y - 1); i < Math.max(y + 1, size - y); i++)
System.out.print('*');
System.out.println();
}
}
or
// two loops
public static void stars(int size) {
for (int y = 0; y < size; y++) {
for (int x = 0; x < size; x++)
System.out.print(
(x >= y && x < size - y) ||
(x >= size - y - 1 && x <= y) ? '*' : ' ');
System.out.println();
}
}
or
// one loop
public static void stars(int size) {
for (int i = 0; i < size * size; i++) {
int y = i / size, x = i % size;
System.out.print(
(x >= y && x < size - y) ||
(x >= size - y - 1 && x <= y) ? '*' : ' ');
if (x == size - 1)
System.out.println();
}
}
Note: Whether this uses one, two or three loops, the time complexity is O(N^2). A simple way to determine this is the number of stars produced is O(N^2) no matter how it is done.

I would do something like this with substrings.
String a = "*******"; //7 stars
String blank = " "; //7 spaces
int j = 7;
for (int i = 0; i < 7; i++) {
if (i > j){
System.out.print(blank.substring(0,i));
System.out.println(a.substring(i,j));
}
else{
System.out.print(blank.substring(0,j));
System.out.println(a.substring(j,i));
}
j--;
}
System.out.println(a);
**Previous edit wouldn't have worked. Changes made.
This works.

Try something like this code I compiled on IDEOne (it seems to work, though):
http://ideone.com/9xZ1YB
class Main
{
public static void main(String[] args)
{
stars();
}
static void stars()
{
final int MAX_WIDTH = 7;
for (int i = 0; i < 7; ++i)
{
int width;
if (i < 3) width = MAX_WIDTH - i * 2;
else if (i > 3) width = (i - 3) * 2 + 1;
else width = 1;
// Before spaces
for (int j = 0; j < (MAX_WIDTH - width) / 2; ++j)
{
System.out.print(" ");
}
// Stars
for (int j = 0; j < width; ++j)
{
System.out.print("*");
}
// After spaces
for (int j = 0; j < (MAX_WIDTH - width) / 2; ++j)
{
System.out.print(" ");
}
System.out.println();
}
}
}

For a beginner in algorithms I would recommend you to break down the structure in sub-parts and then try to solve the pattern.
For this specific pattern it could be broken down into several triangles. Each triangle is then solved by different for loops as shown in the image below.
public static void printPattern(int num) {
// this loop generates first 4 lines
for (int i = 0; i < num / 2 + 1; i++) {
// draws the red triangle of '-'
for (int j = 0; j < i; j++) {
System.out.print("-");
}
// draws the green triangle of '*'
for (int j = i; j < num / 2 + 1; j++) {
System.out.print("*");
}
// draws the blue triangle of '*'
for (int j = i + 1; j < num / 2 + 1; j++) {
System.out.print("*");
}
// draws the orange triangle of '-'
for (int j = 0; j < i; j++) {
System.out.print("-");
}
System.out.println();
}
/* this loop generates last 3 lines */
for (int i = 0; i < num / 2; i++) {
// draws the green triangle of '-'
for (int j = i + 1; j < num / 2; j++) {
System.out.print("-");
}
// draws the red triangle of '*'
for (int j = 0; j < i + 2; j++) {
System.out.print("*");
}
// draws the orange triangle of '*'
for (int j = 0; j < i + 1; j++) {
System.out.print("*");
}
// draws the blue triangle of '-'
for (int j = i + 1; j < num / 2; j++) {
System.out.print("-");
}
System.out.println();
}
}
Using similar technique you could generate any pattern.

If I understood you right, your problem is to print indent in lines 2-7.
Imagine same problem with asterisk symbol replaced by 'x' and whitespace replaced by '-'. Then you need to draw
xxxxxxx
-xxxxx-
--xxx--
---x---
--xxx--
-xxxxx-
xxxxxxx
That means you should output 0, 1, 2 space(s) before asterisks in first, second, thrid strings respectively. I let details for you to figure them out.

public static void stars(/*int jmlBaris*/){
String starstr = "*";
String blank = "_";
int spaceBlank;;
for(int i=7; i>=1;i-=2){
spaceBlank = (7-i)*.5;
String starrep = StringUtils.repeat(starstr, i);
String blankrep = StrinUtils.repeat(blank, spacesBlank);
system.out.println(blankrep + starrep + blankrep);
}
for(int j=3 j<=7; j+=2){
spaceBlank = (7-j)*.5;
starrep = StringUtils.repeat(starstr, j);
String blankrep = StrinUtils.repeat(blank, spacesBlank);
system.out.println(blankrep + starrep + blankrep);
}
}
public static void main(String[] args){
stars();
}

You have little missing to put space on your code. I don't care about right space, who can see that? But left space is very important!!
Try this:
public static void stars(/*int jmlBaris*/) {
for ( int i = 7; i >= 1; i-=2) {
for (int k = 0; k < ((7-i) / 2); k++){ /* Missing Here */
System.out.print(" "); /* Missing Here */
} /* Missing Here */
for (int j = 1; j <= i; j++) {
System.out.print("*");
}
System.out.println("");
}
for (int i = 1; i <= 7; i+=2) {
for (int k = 0; k < ((7-i) / 2); k++){ /* Missing Here */
System.out.print(" "); /* Missing Here */
} /* Missing Here */
for (int j = 1; j <= i; j++){
System.out.print("*");
}
System.out.println("");
}
}

int N = 7;
for (int y=0; y<N; y++)
{
for (int x=0; x<N; x++)
System.out.print( (y-x)*(N-y-x-1)<=0 ? '*' : '-');
System.out.println();
}
or, more symmetrically,
int n = 3;
for (int y=-n; y<=n; y++)
{
for (int x=-n; x<=n; x++)
System.out.print( y*y>=x*x ? '*' : '-');
System.out.println();
}