Java Program to Print Downward Right Triangle Number Pattern - 1
In this program we print a downward right triangle number pattern. The first row prints 1 to 5, and each row after it is one number shorter.
Like every pattern program, it is built from nested loops: the outer loop picks the row, and the inner loops print what goes on that row.
1. The Pattern
For 5 rows the program prints:
Pattern
1 2 3 4 5 1 2 3 4 1 2 3 1 2 1
2. How the Program Works
Here is what each printed line is made of when numberOfRows is 5:
| Line | Leading spaces | Printed after the spaces |
|---|---|---|
| 1 | 0 | 1 2 3 4 5 |
| 2 | 0 | 1 2 3 4 |
| 3 | 0 | 1 2 3 |
| 4 | 0 | 1 2 |
| 5 | 0 | 1 |
- The outer loop counts
rowdown fromnumberOfRowsto 1, so the longest row comes first. - The inner loop prints the numbers from 1 to
row, each followed by a space. System.out.println()moves to the next line after each row.
3. Java Program
public class Pattern7 {
public static void main(String[] args) {
int numberOfRows = 5;
// outer loop for the rows, counting down
for (int row = numberOfRows; row >= 1; row--) {
// inner loop to print the numbers 1 to row
for (int column = 1; column <= row; column++) {
System.out.print(column + " ");
}
// move to the next line
System.out.println();
}
}
}
Output
1 2 3 4 5 1 2 3 4 1 2 3 1 2 1
4. Print the Pattern for Any Number of Rows
To let the user choose the size of the pattern, read the number of rows with a Scanner. The loops stay the same.
import java.util.Scanner;
public class Pattern7Input {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
System.out.print("Enter the number of rows: ");
int numberOfRows = scanner.nextInt();
scanner.close();
// outer loop for the rows, counting down
for (int row = numberOfRows; row >= 1; row--) {
// inner loop to print the numbers 1 to row
for (int column = 1; column <= row; column++) {
System.out.print(column + " ");
}
// move to the next line
System.out.println();
}
}
}
Output (with sample input)
Enter the number of rows: 6 1 2 3 4 5 6 1 2 3 4 5 1 2 3 4 1 2 3 1 2 1
5. Summary
- The outer loop picks the row; the inner loops print the spaces and the numbers for that row.
- Work out how many spaces and which numbers each row needs, then write one inner loop for each.
- Keep
numberOfRowsin a variable, so the same program can print the pattern in any size.
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