Declaration and initialization

Declaration

With the declaration we name a variable and make it known to the compiler. Since each variable name of a data type must be unique, the compiler can also catch the error when trying to declare two variables with the same type and the same name.

Definition

The definition means that a memory area is allocated to a variable. The memory area has a unique address and is used to store values. However, a declaration without definition can also take place. Then both concepts are combined.

Initialization

If we have declared a variable, it has a random value – depending on what is currently in the allocated memory area. Normally you don’t want to work with such random values. Therefore we can use initialization to set the variable to an initial value. Variables should always be initialized to avoid working with a random value.

Code Explanation

LineDescription
1include <iostream> header that defines the standard input/output stream objects
2Namespaces allow to group entities like classes, objects and functions under a name.
4Declaration of the main() function with the return value int
6Declaration of variable integerNumber
9 – 19Declaration and initialization of different variables of different data types
22Initialize the variable integerNumber with the value 1000000000
25 – 37Outputs one variable per line
#include <iostream>
using namespace std;

int main () {
    // variable declaration
    int integerNumber; 

    // variable declaration & initialization
    short shortNumber = 10000; 
    unsigned int unsignedInteger = 10;
    long longNumber = 10000000000;
    unsigned long unsignedLong = 234342;
    double doubleNumber = 5.534;
    long double longDouble = 53453.534;
    float floatNumber = 6.767f;
    char symbol = 'c';
    bool isBoolean= true;
    string charString = "My first string";
    int myArray[] = {16, 24, 35, 41};

    // variable initialization
    integerNumber = 1000000000;

    // variables output
    cout << shortNumber << "\n"
         << integerNumber << "\n"
         << unsignedInteger << "\n"
         << longNumber << "\n"
         << unsignedLong << "\n"
         << doubleNumber << "\n"
         << longDouble << "\n"
         << floatNumber << "\n"
         << symbol << "\n"
         << isBoolean << "\n"
         << charString << "\n"
         << myArray[3] << "\n"
         << endl;
}
Output
10000
1000000000
10
10000000000
234342
5.534
53453.5
6.767
c
1
My first string
41