Data structure is the way you organize data in the main memory during execution of a program.
An array is a collection of similar data elements.
Declaration : int A[5];
Initialization : int B[5]={2,4,6,8,10};
If you have an array of some size and don't define the elements they will become zero by default.
A structure is a collection of data members that are related under one name.
- Defining a structure
struct Rectangle { int length; int width; };
- Size of a structure
The total size of a structure is the sum of its element in memory. An int is 4 bytes.
- Declaring a structure
struct Rectangle r;
struct Rectangle r={10,15} with initialization
- Accessing members
Members are accessed with dot operators.
r.length = 15;
r.width = 10;
A pointer is an address variable that is meant for storing the address of data not the data itself. You cannot use a for each loop on a pointer.
A pointer allows a program to access Heap memory and resources outside of the program.
Pointers are also used for parameter passing.
Data variable == int a = 10;
Address variable == int *p;
Pointer initialization == p = &a;
Use an asterisk * for declaration and dereferencing. The ampersand & is is used when initializing.
Every pointer takes 8 bytes no matter the data type.
A reference is an alias given to a variable. Use an ampersand & to declared a reference. Referencing is useful for parameter passing in small functions. A reference must be initialized when declared.
A pointer uses -> to access a structure instead of a dot operator.
A function is a group of related instructions that performs a specific task. They are also known as modules or procedures. Breaking your program into smaller functions used inside of a main function is called Modular or Procedural programming. One function cannot access the variables of another function.
In call by value, the changes in formal parameters will not affect the actual parameters. Call by value should be used when you want to process something and return the result.
In call by address, the actual parameters address are passed to formal parameters and the formal parameters must be pointers.
In call by reference, the formal function parameters need to ampersand & to to change the actual parameters. It is possible, that the function will run inline depending on the compiler.
Arrays are passed only by address, never by value. When an array is a formal parameter, it's actually a pointer to an array.
A structure can be called by value, address, and reference. When using value, the formal parameters will not affect the actual parameters. In call by reference, the formal parameters will change actual parameters. If the structure contains an array, you can still pass by value.