C Program to Print Floyd's Triangle.

#include <stdio.h>
int main()
{
    int rows, i, j, number= 1;

    printf("Enter number of rows: ");
    scanf("%d",&rows);

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

        printf("\n");
    }

    return 0;
}

Output

1
2 3
4 5 6
7 8 9 10