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More about 2D arrays

In this article, we will learn about some core concepts in 2D arrays such as Printing the left diagonal, right diagonal elements or Printing the elements forming the lower and upper triangle. These problems are extremely important for your exams and placement tests!

Jump to specific sections

The left diagonal
The right diagonal
The lower triangle
The upper triangle

The left diagonal

To access the elements lying on the left diagonal we write -


    #include <stdio.h>
    void main()
    {

    int a[3][3]={ 
            {1,2,3},
            {4,5,6},
            {7,8,9} 
            };

    for(int i = 0 ; i < 3 ; i++)
     {   
        for(int j = 0 ; j < 3 ; j++)
        {
            if(i == j)
            printf("%d",a[i][j]);

            printf(" ");
        }

        printf("\n");
     }

    }

Output

    1
     5
       9

The right diagnol

To print all the elements lying on the right diagonal we write -


    #include <stdio.h>
    void main()
    {

    int a[3][3]={ 
            {1,2,3},
            {4,5,6},
            {7,8,9} 
            };

    for(int i = 0 ; i < 3 ; i++)
        {   
        for(int j = 0 ; j < 3 ; j++)
        {
            if(i+j == 2)
            printf("%d",a[i][j]);

            printf(" ");
        }

        printf("\n");
        }

    }

Output

        3
      5
    7

The lower triangle

All the elements present on the left diagonal or lying below the left diagonal are included in the lower triangle. To print all the elements lying on the lower triangle, we write -


    #include <stdio.h>
    void main()
    {

        int a[3][3]={ 
            {1,2,3},
            {4,5,6},
            {7,8,9} 
          };

        for(int i = 0 ; i < 3 ; i++)
        {   
            for(int j = 0 ; j < 3 ; j++)
            {
                if(i >= j)
                printf("%d",a[i][j]);

                printf(" ");
            }

            printf("\n");

        }
    }

Output

    1
    4 5
    7 8 9

The upper triangle

All the elements present on the right diagonal or lying below it are included in the upper triangle. To print them, we write -


        #include <stdio.h>
        void main()
        {
    
            int a[3][3]={ 
                {1,2,3},
                {4,5,6},
                {7,8,9} 
              };
    
            for(int i = 0 ; i < 3 ; i++)
            {   
                for(int j = 0 ; j < 3 ; j++)
                {
                    if(i <= j)
                    printf("%d",a[i][j]);
                    else
                    printf(" ");

                    printf(" ");
                }
    
                printf("\n");
    
            }
        }

Output

    1 2 3 
      5 6 
        9