need some printing number pyramid - c

Question

I need to program a number pattern pyramid like that:
Here is my code:
#include<stdio.h>
int main()
{
int i, j, rows = 5;
for (i = 1; i <= 5; i++)
{
for (j = 1; j <= i; j++)
{
printf("%d ", j);
}
printf("\n");
}
for (i = 0; i <= 5; i++)
{
for (j = 0; j <= i; j++)
{
printf("%d ", j);
}
printf("\n");
}
}
Where am I doing wrong? I need to flip somehow the first triangle pattern and mix it with the second. Please help.

Answer 1

Your pyramid is 6 levels high. The max number is 5. This is not a coincidence. There is a direct relationship.
If n is 5, you need to do something 6 times, from 0 to n. There's a loop.
for (int i = 0; i <= n; i++) {
...
}
On each row you need to do print from i to 0, and then from 1 to i. That's two loops.
for (int j = i; j > 0; j--) {
...
}
for (int j = 1; j <= i; j++) {
...
}
Of course, you also need to indent a number of spaces inversely related to i, which is another loop.
for (int j = 0; j <= /* Fill in here for inverse relationship */; j++) {
...
}

Answer 2

I need to flip somehow the first triangle pattern and mix it with the second.
TL;DR The trick is very simple: your row index i should start from |n - j| (or abs(n - j)) where j is the column index and n is the number.
Here is how you can do it:
for (int j = 0; j < ncols; ++j) {
for (int i = abs(n - j); i < nrows; ++i) {
matrix[i][j] = '0' + abs(n - j);
}
}
Explanation:
Imagine you have a matrix. In order to build a pyramid with a number n, you will need:
n + 1 rows (since you will have 0 included in the top). Let's call it nrows.
2n + 1 columns (2n because the numbers will appear twice in a row, 1 because you will have one 0 per row). Let's call it ncols.
0 1 2 3 4 5 6 7 8 9 10
- - - - - - - - - - -
0 | 0
1 | 1 0 1
2 | 2 1 0 1 2
3 | 3 2 1 0 1 2 3
4 | 4 3 2 1 0 1 2 3 4
5 | 5 4 3 2 1 0 1 2 3 4 5
First, you want to fill the first half, i.e. from column 0 to n: for (int j = 0; j <= n; ++j).
J | End | Start | Pattern of Start
---------------------------------------
0 | N | N | N - 0
---------------------------------------
1 | N | N - 1 | N - 1
---------------------------------------
2 | N | N - 2 | N - 2
---------------------------------------
... | ... | ..... | N - J
---------------------------------------
N | N | 0 | N - N
The pattern is: for (int i = n - j; i < nrows; ++i). You would fill that first half with n - j.
Second, you want to fill the second half, i.e. from column n + 1 to 2n: for (int j = n + 1; j < ncols; ++j).
J | End | Start | Pattern of Start
------------------------------------------
N + 1 | N | 1 | N + 1 - N = J - N
------------------------------------------
N + 2 | N | 2 | N + 2 - N = J - N
------------------------------------------
N + 3 | N | 3 | N + 3 - N = J - N
------------------------------------------
..... | ... | ..... | N + X - N = J - N
------------------------------------------
2N | N | N | 2N - N = J - N
The pattern is: for (int i = j - n; i < nrows; ++i). You would fill that second half with j - n.
Now, you can do two separate for loops to fill the first and second halves.
// Fill first half
for (int j = 0; j <= n; ++j) {
for (int i = n - j; i < nrows; ++i) {
matrix[i][j] = '0' + n - j;
}
}
// Fill second half
for (int j = n + 1; j < ncols; ++j) {
for (int i = j - n; i < nrows; ++i) {
matrix[i][j] = '0' + j - n;
}
}
You can write one for loop by replacing n - j and j - n with abs(n - j), since both of them are positive values (see TL;DR above, or the code below).
Full functionning code:
#include <stdio.h>
#include <stdlib.h>
void print_matrix(const int nrows, const int ncols, const char matrix[nrows][ncols])
{
for (int i = 0; i < nrows; ++i) {
for (int j = 0; j < ncols; ++j)
printf("%c ", matrix[i][j]);
printf("\n");
}
}
void init_matrix(const int nrows, const int ncols, char matrix[nrows][ncols], const char value)
{
for (int i = 0; i < nrows; ++i)
for (int j = 0; j < ncols; ++j)
matrix[i][j] = value;
}
void print_pyramid(const int n)
{
// Calculate the number of rows and columns
const int nrows = n + 1;
const int ncols = n * 2 + 1;
char matrix[nrows][ncols];
// Initialization
init_matrix(nrows, ncols, matrix, '\0');
// Fill the matrix
for (int j = 0; j < ncols; ++j) {
for (int i = abs(n - j); i < nrows; ++i) {
matrix[i][j] = '0' + abs(n - j);
}
}
// Printing
print_matrix(nrows, ncols, matrix);
}
int main(void)
{
print_pyramid(5);
}

Answer 3

You have to include all 3 for loops in one for loop which runs 6 times. First you have to print spaces. Then first half of the triangle and then the other half. After that you have to print \n .
#include<stdio.h>
int main()
{
int i, j,k,l;
for (i = 0; i <=5; i++)
{
for (j = 5; j > i; j--)
{
printf(" ");
}
for (k = i; k >=0; k--)
{
printf("%d ", k);
}
for (l = 1; l <=i; l++)
{
printf("%d ", l);
}
printf("\n");
}
}