part12.1

Two-Dimensional Arrays

What is a two-dimensional array ?
- A collection of variables having the same data type
- The variables are thought as being structured in two dimensions
- Each variable is accessed using:
(i) a name which is the same for all of them
(ii) a pair of indices that represent the position of the variable in each dimension

- In other words, a two-dimensional array is an array of arrays !!
Declaring two-dimensional arrays
- Specify the type of the variables followed by the size in each dimension

DataType ArrayName [ConstIntExpression][ConstIntExpression]
Accessing individual components

ArrayName [IndexExpression][IndexExpression]

- The IndexExpression may be just a constant, or a variable or even an expression
- The result of IndexExpression must be an integer value
- Examples: value[4][1], value[2*a+1][a-1] (assuming a is an integer)
Each array element can be treated the exactly the same way as a simple variable
- Assign a value: value[2][3]=100;
- Read a value into it: cin >> value[2][3];
- Write its contents: cout << value[2][3];
- Pass it as a parameter: y=sqrt[value[2][3]);
Initializing two-dimensional arrays
- Two-dimensional arrays can be initialized in a declaration
```
int value[2][3] = 
{
  {10, 20, 12}
  {13, 33, 45}
};
```
- Two-dimensional arrays can also be initialized using two loop statements:
Aggregate operations
- No aggregate operations (assignment, comparison, arithmetic, etc.)
- Passing a two-dimensional array to a function ? Yes !!
Processing two-dimensional arrays
- Sum the rows
- Sum the columns
- Sum all the elements
- Print the table

Sum the rows

- Compute the average temperature per week

for(i=0; i<52; i++)
{
 sum = 0.0;
 for(j=0; j<7; j++)
   sum = sum + temperature[i][j];

 average = sum / 7;
 cout << "The average temperature of the " << i << "-th week is " << average << endl;
}

Sum the columns

- Compute the average temperature for each day of the week

for(j=0; j<7; j++) 
{ 
 sum = 0.0; 
 for(i=0; i<52; i++) 
   sum = sum + temperature[i][j]; 
 
 average = sum / 52; 
 cout << "The average temperature of the " << j << "-th day is " << average << endl; 
}

Sum all the elements

- Compute the average temperature of the year

sum = 0.0;
for(i=0; i<52; i++)
 for(j=0; j<7; j++) 
   sum = sum + temperature[i][j]; 
 
 average = sum / (7*52); 
 cout << "The average temperature of the year is " << average << endl; 
}

Print the temperatures

- Week by week

for(i=0; i<52; i++) 
{
 for(j=0; j<7; j++)
   cout << temperature[i][j] << " ";
 cout << endl;
}

- Day by day

for(j=0; j<7; j++)
{ 
  for(i=0; i<52; i++) 
    cout << temperature[i][j] << " "; 
 cout << endl; 
}