Arrays 2d Arrays 2d Arrays 2d Arrrays 2d

©LPU CSE101 C Programming
CSE101-Lec#17(Part-2)
• Multidimensional Arrays(2D Array)

2D-Array
• The basic form of declaring a two-dimensional array of size x,
y:
• Syntax:
• data_type array_name[x][y];
• data_type: Type of data to be stored. Valid C/C++ data type.
• We can declare a two dimensional integer array say ‘x’ of size
10,20 as:
• int x[10][20];
• Elements in two-dimensional arrays are commonly referred by
x[i][j] where i is the row number and ‘j’ is the column number

2D-Array
• A two – dimensional array can be seen as a table with ‘x’ rows
and ‘y’ columns where the row number ranges from 0 to (x-1)
and column number ranges from 0 to (y-1). A two –
dimensional array ‘x’ with 3 rows and 3 columns is shown
below:

Also known as Multiple-Subscripted Arrays
• Multiple subscripted arrays
– Tables with rows and columns (m by n array)
– Like matrices: specify row, then column
int a[rows][column];
4
Row 0
Row 1
Row 2
Column 0
0
Column 1 Column 2 Column 3
a[ 0 ][ 0 ]
a[ 1 ][ 0 ]
a[ 2 ][ 0 ]
a[ 0 ][ 1 ]
a[ 1 ][ 1 ]
a[ 2 ][ 1 ]
a[ 0 ][ 2 ]
a[ 1 ][ 2 ]
a[ 2 ][ 2 ]
a[ 0 ][ 3 ]
a[ 1 ][ 3 ]
a[ 2 ][ 3 ]
Row subscript
Array name
Column subscript

Memory representation of 2D-Array
• A 2D array’s elements are stored in continuous memory locations. It can
be represented in memory using any of the following two ways:
1. Column-Major Order
2. Row-Major Order
1. Column-Major Order:
In this method the elements are stored column wise, i.e. m elements of
first column are stored in first m locations, m elements of second column
are stored in next m locations and so on. E.g.
A 3 x 4 array will stored as below:

Memory representation of 2D-Array
• 2. Row-Major Order:
In this method the elements are stored row wise, i.e. n
elements of first row are stored in first n locations, n elements
of second row are stored in next n locations and so on. E.g.
A 3 x 4 array will stored as below:

Initialization
1) Initializing at the point of declaration:
• int a[ 2 ][ 2 ] = { { 1, 2 }, { 3, 4 } };
Initializers grouped by row in braces
• If not enough, unspecified elements set to zero
• Int a[ 2 ][ 2 ] = { { 1 }, { 3, 4 } };
• int a3[2][2]={1,2};//Remaining elements are zero
• int a4[2][2]={0};//All elements are zero
1 2
3 4
1 0
3 4

Initialization
• int a5[][2]={1,2,3};//It is possible to skip row size, if
elements are initialized at the point of declaration
• int a[2][]={1,2,3};//Not possible to skip column
size[Error will come]
• int a[][]={1,2,3};//Not possible to skip both row and
column size[Error will come]

Initialization
2) Taking input from user
int a[3][3], i, j;
for(i=0; i<3; i++)
{ // for loop for rows
for(j=0; j<3;j++)
{ // for loop for columns
printf(“enter the value ofa[%d][%d]: ”, i, j);
scanf(“%d”, &a[i][j]);
} //end for columns
} //end for rows

Program to
display 2D
array
#include<stdio.h>
void main()
{
int a[3][3], i, j;
for(i=0; i<3; i++)
{ // for loop for rows
for(j=0; j<3;j++)
{ // for loop for columns
printf(“enter the value of a[%d][%d]: ”, i, j);
scanf(“%d”, &a[i][j]);
} //end for columns
} //end for rows
printf(“elements of 2D matrix are”);
for(i=0; i<3; i++)
{
for(j=0;j<3;j++)
{
print(“%dt”, a[i][j]);
} //end for
printf(“n”);
} //end for
} //end main

enter the value of a[0][1] :1
Element of 2D matrix are:
1 2 3
4 5 6
7 8 9

Matrix operations using 2D arrays
• WAP to find the sum of two matrices
• WAP to display the transpose of a matrix
• WAP to find the sum of diagonal elements of a
matrix
• WAP to perform multiplication of 2 matrices
and display the result

WAP to find the sum of two matrices
#include <stdio.h>
int main()
{
float a[3][3], b[3][3], c[3][3];
int i, j;
printf("Enter elements of 1st matrixn");
for(i=0; i<3; i++)
{
for(j=0; j<3 ;j++)
{
printf("Enter a%d%d: ", i, j);
scanf("%f", &a[i][j]);
}
}
// Taking input using nested for loop
printf("Enter elements of 2nd matrixn");
for(i=0; i<3; i++)
{
for(j=0; j<3; j++)
{
printf("Enter b%d%d: ", i, j);
scanf("%f", &b[i][j]);
}
}
// adding corresponding elements of two arrays
for(i=0; i<3; i++)
{
for(j=0; j<3; j++)
{
c[i][j] = a[i][j] + b[i][j];
}
}
// Displaying the sum
printf("nSum Of Matrix:n");
for(i=0; i<3; i++)
{
for(j=0; j<3; j++)
{
printf("%.1ft", c[i][j]);
}
printf("n");
}
return 0;
}

WAP to display the transpose of a matrix
#include <stdio.h>
int main()
{
int a[10][10], transpose[10][10], r, c, i, j;
printf("Enter rows and columns of matrix: ");
scanf("%d %d", &r, &c);
// Storing elements of the matrix
printf("nEnter elements of matrix:n");
for(i=0; i<r; i++)
{
for(j=0; j<c; j++)
{
printf("Enter element a%d%d: ",i, j);
scanf("%d", &a[i][j]);
}
}
// Displaying the matrix a[][] */
printf("nEntered Matrix: n");
for(i=0; i<r; i++)
{
for(j=0; j<c; j++)
{
printf("%d ", a[i][j]);
}
printf("nn");
}
// Finding the transpose of matrix a
for(i=0; i<r; i++)
{
for(j=0; j<c; j++)
{
transpose[i][j] = a[j][i];
}
}
// Displaying the transpose of matrix a
printf("nTranspose of Matrix:n");
for(i=0; i<r; i++)
{
for(j=0; j<c; j++)
{
printf("%d ",transpose[i][j]);
}
printf("nn");
}
return 0;
}

WAP to find the sum of diagonal elements of a matrix
#include<stdio.h>
int main()
{
int a[10][10],sum=0;
int i,j,m,n;
printf("Enter number of rows and
column:");
scanf("%d%d",&m,&n);
printf("Enter Elements : ");
for(i=0;i<m;i++)
{
for(j=0;j<n;j++)
{
scanf("%d",&a[i][j]);
}
}
for(i=0;i<m;i++)
{
for(j=0;j<n;j++)
{
if(i==j)
{
sum=sum+a[i][j];
}
}
}
printf("Sum of Diagonal
Elements = %d ",sum);
}

WAP to perform multiplication of 2 matrices and display the result
#include <stdio.h>
int main()
{
int a[10][10], b[10][10], result[10][10], r1, c1, r2, c2, i, j, k;
printf("Enter rows and column for first matrix: ");
scanf("%d %d", &r1, &c1);
printf("Enter rows and column for second matrix: ");
scanf("%d %d",&r2, &c2);
// Column of first matrix should be equal to column of second matrix and
while (c1 != r2)
{
printf("Error! No. of columns of first matrix not equal to no.of row of
second.nn");
printf("Enter rows and column for first matrix: ");
scanf("%d %d", &r1, &c1);
printf("Enter rows and column for second matrix: ");
scanf("%d %d",&r2, &c2);
}
// Storing elements of first matrix.
printf("nEnter elements of matrix 1:n");
for(i=0; i<r1; i++)
{
for(j=0; j<c1; j++)
{
printf("Enter elements a%d%d: ",i,j);
scanf("%d", &a[i][j]);
}
}
// Storing elements of second matrix.
printf("nEnter elements of matrix 2:n");
for(i=0; i<r2; i++)
{
for(j=0; j<c2; j++)
{
printf("Enter elements b%d%d: ",i, j);
scanf("%d",&b[i][j]);
}
// Initializing all elements of result matrix to 0
for(i=0; i<r1; i++)
{
for(j=0; j<c2; j++)
{
result[i][j] = 0;
}
}
// Multiplying matrices a and b and
// storing result in result matrix
for(i=0; i<r1; i++)
{
for(j=0; j<c2; j++)
{
for(k=0; k<c1; k++)
{
result[i][j]+=a[i][k]*b[k][j];
}
}
}
// Displaying the result
printf("nOutput Matrix:n");
for(i=0; i<r1; i++)
{
for(j=0; j<c2; j++)
{
printf("%d ", result[i][j]);
}
printf("nn");
}
return 0;
• }

Dry running

Q1
What will be the output of following code?
#include<stdio.h>
int main()
{
int a[][3]={1,2,3,4,5,6};
printf("%d",a[0][2]);
return 0;
}
A. 2
B. 3
C. 4
D. Compile time error

Q2
Which of the following is invalid initialization of 2D Array?
A. int a[][2]={1,2,3,4};
B. int a[2][2]={1,2,3,4};
C. int a[2][]={1,2,3,4};
D. int a[2][2]={};

Q3
What will be the output of following code?
#include<stdio.h>
int main()
{
int a[3][2]={{1,2},{3,4},{5,6}};
printf("%d",a[1][1]*a[2][1]);
return 0;
}
A. 24
B. 12
C. 8
D. 20

Arrays 2d Arrays 2d Arrays 2d Arrrays 2d

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