Upside-down triangle of numbers

Question

I'm a beginner to Java and can't figure out how to print an upside down triangle of numbers. The numbers should decrease in value by 1 for each row. Ex. Number of rows: 6;

Print:

So far this is what I came up with; (int nr is scanned input from user)

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

By having nr--; the loop gets shorter and I cant figure out how to keep the loop going for nr-times, yet still decreasing the amount of numbers printed out.

score 1 · Answer 1 · answered Feb 05 '16 at 19:25

1

You are right in that you need to write a loop to print a line for each number, starting at nr and decreasing by 1 until you get to 0. But you also have to print a variable number of numbers at each line. To do that, a nested loop could be used to print the number the amount of times necessary.

Since you start printing at nr and decrease until you reach 1, you could try writing an outer loop that decrements rather than increments. Then use a nested loop to print the number the required number of times. For example:

for (int i = nr; i > 0; i--) {
    for (int j = 0; j < i; j++) {
        System.out.print(i);
    }
    System.out.println();
}

answered Feb 05 '16 at 19:25

Spencer

176
5

Thank you! This might be a dumb question, but if int i starts out as 0, and decreases by -1, why doesn't (i) print out as -1, -2 etc.? – floval Feb 08 '16 at 17:50
Int i starts out at nr, not 0. It decreases until the condition inside the for loop, i > 0, is false. That condition becomes false when i decrements from 1 to 0, and the loop breaks. – Spencer Feb 08 '16 at 18:20

score 1 · Answer 2 · 2021-04-01T20:59:43.267

In this case, you can use a single while loop and two decreasing variables:

i - number of the row - from 6 to 1
j - number of repetitions in the row - from i to 1:

int i = 6, j = i;
while (i > 0) {
    if (j > 0) {
        // print 'i' element 'j' times
        System.out.print(i);
        --j;
    } else {
        // start new line
        System.out.println();
        j = --i;
    }
}

Output:

^{See also: Printing a squares triangle. How to mirror numbers?}

score 0 · Answer 3 · edited Apr 01 '21 at 17:52

0

Your problem is that you are changing nr, try:

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

edited Apr 01 '21 at 17:52

Community

1
1

answered Feb 05 '16 at 19:19

Martín Muñoz del Río

1,958
11
14

Andreas · Answer 4 · 2016-02-05T19:32:00.730

0

You can't decrease nr and still use it as upper limit in the loops. You should in fact consider nr to be immutable.

Instead, change outer loop to count from nr down to 1, and inner loop to count from 1 to i, and print value of i.

for (int i = nr; i > 0; i--) {
    for (int j = 0; j < i; j++) {
        System.out.print(i);
    }
    System.out.println();
}

edited Feb 05 '16 at 19:32

answered Feb 05 '16 at 19:21

Andreas

154,647
11
152
247

Upside-down triangle of numbers

4 Answers4