How to print Floyd's triangle (of integers) using C program?

Floyd's triangle is a right-angle triangle of consecutive numbers, starting with 1 in the top left corner. Each row contains one more number than the previous row, forming a triangular pattern −

1
2 3
4 5 6
7 8 9 10

Syntax

for (i = 1; i <= rows; i++) {
    for (j = 1; j <= i; j++) {
        printf("%d ", number);
        number++;
    }
    printf("<br>");
}

Example 1: Basic Floyd's Triangle

This program generates Floyd's triangle by printing consecutive numbers row by row −

#include <stdio.h>

int main() {
    int rows, i, j, start = 1;
    
    printf("Enter number of rows: ");
    scanf("%d", &rows);
    
    for (i = 1; i <= rows; i++) {
        for (j = 1; j <= i; j++) {
            printf("%d ", start);
            start++;
        }
        printf("<br>");
    }
    
    return 0;
}

Enter number of rows: 5
1 
2 3 
4 5 6 
7 8 9 10 
11 12 13 14 15 

Example 2: Reverse Floyd's Triangle

This program creates a reverse Floyd's triangle by starting with the largest number and decrementing −

#include <stdio.h>

int main() {
    int rows, i, j;
    
    printf("Enter number of rows: ");
    scanf("%d", &rows);
    
    int k = rows * (rows + 1) / 2;
    
    for (i = rows; i >= 1; i--) {
        for (j = 1; j <= i; j++) {
            printf("%4d", k--);
        }
        printf("<br>");
    }
    
    return 0;
}

Enter number of rows: 5
  15  14  13  12  11
  10   9   8   7
   6   5   4
   3   2
   1

How It Works

• Outer loop: Controls the number of rows (from 1 to rows)
• Inner loop: Prints numbers in each row (j numbers in the j-th row)
• Counter variable: Keeps track of the current number to print
• Formula: Total numbers in n rows = n*(n+1)/2

Conclusion

Floyd's triangle demonstrates nested loops and sequential number generation. The pattern is useful for understanding triangular number sequences and can be modified to create variations like reverse triangles.