Variables, also referred to as "identifiers" are named memory locations that have a type, such as an integer or character, and consequently, a size, which is inherited from their type. Since variables are types, they have a set of operations that can be used to change or manipulate them.
An identifier name can be made up of only the following:
There are some reserved words in C++, so the programmer should be cautious in his choice of identifier names. For example, "int" is a poor choice, since that is a reserved word indicating the type of the variable.
char | A 1 byte integer usually used to store a character. |
short | A 2 byte integer. |
int | A 4 byte integer. |
long | 4 or 8 byte integer (compiler dependent). |
float | Single precision floating point number.
(7 digits or more - compiler dependent) |
double | Double precision floating point number.
(15 digits or more - compiler dependent) |
bool | Boolean literal. Values are true (numerically=1) or false (numerically=0). |
string | A variable number of characters.
Note: string is actually a C++ class. In order to use this datatype, you need to add the statement: #include <string> to the start of your program. |
Arrays are fixed-sized sequential collections of elements of the same type.
We can refer to the elements in the array as the first element,
second element, and so forth until we get to the last element.
To set up an array, use this command:
variable_type array_name[no_of_elements];
Notice the square brackets used for the subscripts.
Use these also when you want to reference an array element.
To refer to an index (individual element) within the array, use
array_name[index]
.
In C/C++, the index of the first element is zero (0), and the index of
the last element is no_of_elements - 1.
The simplest example of a "one dimensional" array is a simple list
such as a shopping list with one item per line.
e.g. General Format for declaring a one-dimensional array:
data_type variable_name [ no_of_elements ]
Or, for a two-dimensional array:
data_type
variable_name [ no_of_rows ][ no_of_columns ]
A familiar example of a two dimensional array is what you
see when you use a spreadsheet program.
There are cells organized into a grid of rows and columns.
e.g. Declare an integer array of 2 rows, 3 columns:
int Nums[2][3];
Often you will see a constant declared to hold the array size,
and then this constant used in the array declaration.
i.e.
const R_size = 2;
const C_size = 3;
int Nums[R_size][C_size];
Array elements can also be initialized when the array is declared.
int Nums[2][3] = { {1, 2, 3}, {4, 5, 6} };
Here is a sample program that uses a one-dimensional array. This short program computes the sum of all the values found within the array. Take note of the differences between this and the one written in Pascal.
#include <iostream> using namespace std; int main() { int i, sum = 0; int numbers[5] = {3, 7, 2, 4, 5}; // defines the array and initializes a value to each // element of the array for (i = 0; i < 5; i++) sum += numbers[i]; cout << "sum = " << sum << endl; }
When compiled, the program will print out: sum = 21
Each variable in your program nust be declared and initialized. There are two ways in which we can do this. We can declare our variables first, like this:
char letter; string first_name; int x; long student_id; float payRate; double pi; bool valid; int Nums[2][3];
then initialize them later in the program as a separate statement.
letter = 'A'; first_name = "Ada"; x = 7; student_id = 200201202; payRate = 12.85; pi = 3.1415926536; valid = true; Nums[0][0] = 1; Nums[0][1] = 2; Nums[0][2] = 3; Nums[1][0] = 4; Nums[1][1] = 5; Nums[1][2] = 6;
The other way is to initialize them at the same time as they are declared (in one statement).
char letter = 'A'; string first_name("Ada"); int x = 7; long student_id = 200201202; double pi = 3.1415926536; float payRate = 12.85; bool valid = true; int Nums[2][3] = { {1, 2, 3}, {4, 5, 6} };
We can also declare our initialized variable as a constant, by adding the type qualifier const before the definition. The general format for a const declaration is shown below:
const type variable-name = any value you like
Inside of a program, you will see constants written like this:
const float payRate = 12.85; const double pi = 3.1415926536;
But the programmer can also force the conversion of datatypes by type casting a value. It is simple to do, just put the data type and parentheses around the value that you want to cast.
e.g. int_value = int( float_value / 2 );
This page has been accessed
times.
Last modified: Friday, 21-Aug-2020 15:28:13 CST
Copyright 2000 Department of Computer Science, University of Regina.