How do this program but in reverse, pattern-CodePudding

so i want output like this

i already make the program but it only output these, and im confused how to output the bottom triangle

  1
 123
12345

here's my program

#include <iostream>
using namespace std;

int main() {
    int n = 3 ;
    int i, j, k;


        for (i = 1; i <= n; i  ) {
            for (j = n; j > i; j--) {
                cout << " ";
            }
            for (k = 1; k <= (2 * i - 1); k  ) {
                cout << k;
            }
        cout <<endl;
        }

return 0;
}

CodePudding user response：

@Mojtaba's answer is a perffect extension to your approach.

However, I wanted to provide another method that is generally used in creating such strings that are formatted in a particular manner. It is common to create the entire pattern line by line and then print to the console all at once.

I have appropriately commented the code for your reference and it should be easy to understand:

#include <iostream>
#include <vector>

void pattern(int n) {
    std::vector<std::string> lines; // store the first n lines to print later
    int length = 2*n - 1; // length of each line

    for(int i = 0; i < n; i  ) {
        std::string str = std::string(length, ' '); 
        for(int j = 1; j <= 2*i   1; j  ) {
            str[n - i   j - 2] = j   '0'; 
            // indexing can be figured by observing the pattern
        }
        lines.emplace_back(str);
    }

    for(int i = 0; i < n; i  ) {
        std::cout << lines[i] << std::endl;
    }
    
    for(int i = n-2; i >= 0; i--) {
        std::cout << lines[i] << std::endl;
    }

    return;
}

int main() {
    int n;
    std::cin >> n;

    pattern(n);
}

CodePudding user response：

I added another for loop exactly like yours with different order from n-1. I modified your code to this:

int main() {
    int n = 3 ;
    int i, j, k;


    for (i = 1; i <= n; i  ) {
        for (j = n; j > i; j--) {
            cout << " ";
        }
        for (k = 1; k <= (2 * i - 1); k  ) {
            cout << k;
        }
        cout <<endl;
    }

    for (i = n - 1; i >= 1; i--) {
        for (j = n; j > i; j--) {
            cout << " ";
        }
        for (k = 1; k <= (2 * i - 1); k  ) {
            cout << k;
        }
        cout <<endl;
    }

    return 0;
}

Now it returns: