C program to print L diagonal triangle:

void main()

{

                int i=0,j=0;

                int arr[rows][cols];

                for (i=0; i<=rows-1; i++)

                                for(j=0;j<=cols-1;j++)

                                {

                                                printf("Enter elements (%d,%d)\n",(i+1),(j+1));

                                                scanf("%d",&arr[i][j]);

                                }

                for (i=0; i<=rows-1; i++)

                {

                                printf("\t");       

                                for(j=0;j<3;j++)

                                                {

                                                printf("%d  ",arr[i][j]);

                                                }

                                                printf("\n");

                }

                printf("\n Revers of matrix\n");

                for(i=0;i<=rows-1;i++)

                {

                                printf("\t");

                                for(j=0;j<=cols-1;j++)

                                {

                                                if(i==j)

                                                printf("%d  ",arr[i][j]);

                                                else

                                                                printf("   ");

                                }

                                                printf("\n");

                }

}