Discussion

C as a Programming Language:

• Programming as logic
• Language as grammar and syntax
• Procedural
• Modular
• Abstraction/Hiding
• Object-Oriented
• C++: Parametrization or Generic Programming

Building:

• Generating an executable from code
• Concept of Makefile

Compiling:

• Preprocessing – cpp
• Compiling – gcc
• Some important flags (-o, -c, -Wall, -L, -I, -l, -g, -O, -D, -Wl,)
• Cross compiling

Directives and Include:

• #include
• #define
• #ifdef
• Include guards
• What's in the include?
• Include path “”, <>

General Guidelines

• Maintainability/Readability
• Flexibility/Scalability – Growth and Reduction
• Usability
• Re-usability of Code

Empty Program

• Every statement ends with ;
• Space insensitive
• {} scopes
• A brief intro to functions
• main

Data Types

• Primitive/Built-in data type controls:
• Typical types
  • double, float
  • int, short, long, long long
  • unsigned, unsigned short, unsigned long, unsigned long long
  • char, unsigned char – ASCII
• typedef (architecture example)

Variables

• Data Type (Domain)
• Scope – Variables on stack
• Declaration
• Global variables
• Qualifiers
  • static
  • extern

Data Represenation

• Writing constants
• Chars
• printf
• scanf

Operators

(type)  Cast Operator
[ ]  Array Subscript
a.b  a Member of b
a->b a Member by pointer b
}

• Unary (pre/post++, !, ~, &, *)

++a Prefix Increment
a++ Postfix Increment
!   Not
&   Address-of 
*   Indirection of (used mainly with Pointers)
~   

• Arithmetic (*,/,%,+,-)
• Bitwise (>>,<<,&,^,|)

==
    is equal to
!=
    is not equal to
>
    is greater than
<
    is less than
>=
    is greater than or equal to
<=
    is less than or equal to 

• Logical (&&, ||)

&&  Logical AND
    is logical AND same meaning as the AND operator
||  Logical OR
    is logical OR same meaning as the OR operator

• Conditional (? :)

Precedence

• Who gets processed First?
• Primary
• Unary (Right associative)

Casting

• Explicit cast
• Implicit cast

Code Example

//Declaration
int x; char c = 'k';
int x, y;

//Explicit Casting
char x = 'a'; int y = (int) x;
int x = 5; char y = (char) x;

// Implicit cast
double a, b, c; int x; c = a*b + x;
x = a*b + c;

Pointers, the short version!

Actually, pointers are not exactly references. A pointer is a normal variable but it carries the memory address of another variable. That other variable can be a premitive type (char, int, bool, long, ..) or an aggregate type (Object, structure, array, ...) or a function (pointers to functions).

A point could point to anything (reference anything), that could be a pointer to an object of a class , a pointer to a structure, a point to int, to char … to anything actually. A major difference between a pointer and references is that references are managed, wether in java or .net or any other dynamic language.

A managed environment means that your JVM or .net CLR, takes care of a lot of things for you…

One of the most important of these things are pointers. To be specific, java has no pointers at all, just references. c# does support pointers.

Anyway, in c and c++ you can use a pointer to point to anything simply as follows:

int* p ;
char* p;

this is the declaration, it doesn’t point to anything now… in other languages, if you tried to use this pointer it will throw an exception , in c it wont it will simply get you the value that originally existed in the place you are pointing to… and if you attempted to write to it, you will overwrite someone else’s data or in best cases you will write in a random place where no one knows if it is used or not.

It's IMPORTANT and considered a best practice to initialize your pointers (Use NULL if you don't yet know what they will point to). Pointers are randomly initialized. If you try to access it without initializing, you can get a SEGV when you read from it and/or write to it. Depending on the random "value" it points to.

pointers are used for multiple reasons. I can't remember all of them:

• C has no "pass by reference". You actually pass the memory address by value here (To change the value of a pointer, you need to pass a pointer to a pointer).
• Pass by value can be bad if you have a large data structure!
• Some data structures can only be passed as pointers.
• In C, you can't practically do strings without pointers.
• No dynamic memory allocation without pointers.
• The array declaaration is a pointer to the 1st element of the array!
• Pointers to functions are important also!

You can get the address of any variable in c using the & operator:

int  x = 0;
int* p = &x;

that way, p is pointer that points to x. to get the value in x we use the * operator:

*p  = 6; 

You could a pointer value to another with no problems:

nt* p2 = p; 

an important usage of the pointer is passing a variable by reference if we have a function as follows:

void  SomeFunctionName (int s)
{
	S = 5;
} 

And used as follows:

int x = 2;
SomeFunctionName(x);

Actually, this didn’t do anything… x will still be 2, because it is called by value, that means it sent a copy of its value to s..

It is important to note that c does not have have out-of-the-box pass by reference.

Written like this:

void  SomeFunctionName (int* s)
{
	*S = 5;
}

And used as follow:

int x = 2;
SomeFunctionName (&x);

In c an array is a pointer to the first element of the array. The point here is the dynamic allocation... Note: add the lib where the function malloc exist in malloc.h and in the code:

int* ar = (int*)malloc (10 * sizeof(int));

note: that in c you can say the following:

ar++;

What if I want to pass an array to a function I would do the following:

void foo (int* par)
{
      par[3] = 3;
}

And pass it using the following:

foo(ar);

If I tried to do that the way in the previous example, like the following:

void foo(int* par)
{
      par = (int*)malloc (10 * sizeof(int));
}

And pass it using the following:

foo(ar);

Nothing will happen, we have changed what the pointer “par” points to not what the original array points to…

For this to work, we need to make a pointer to pointer… That is written like this:

int** pp = &ar;

here we are assigning the address of the ar pointer to pp… that way we can do the following:

*pp  =  (int*)malloc (10 * sizeof(int));

That will change the value of ar… Thus we could do the following to the function:

void foo(int** par)
{
*par = (int*)malloc (10 * sizeof(int));
}

And pass it using the following:

foo(&ar);

That’s all… my goal was to overview the pointers briefly… you will have some long book in the c to get it all but this is the short version… Thank you.

Simple Examples

Simple Examples

Example 1: Prints Hello World

#include <stdio.h>

int main()
{
  printf( "Hello World\n" );
  return 0;
}

Example 2: Declare Variables

#include <stdio.h>
int main() 
{
    int x;
    printf( "Declare x first\n" );
    return 0;
}

Example 3: If Else

#include <stdio.h>	

int main()            /* Most important part of the program! */
{
    int age;                          /* Need a variable... */
    printf( "Please enter your age" );  /* Asks for age */
    scanf( "%d", &age );                 /* The input is put in age */
    if ( age < 100 ) {                  /* If the age is less than 100 */
    printf ("You are pretty young!\n" ); /* Just to show you it works... */
  }
else if ( age == 100 ) {            /* I use else just to show an example */ 
     printf( "You are old\n" );       
  }
  else {
    printf( "You are really old\n" );     /* Executed if no other 
statement is */
  }
  return 0;
}

Example 4: For Loop

#include <stdio.h>

int main()
{
    int x;
    /* The loop goes while x < 10, and x increases by one every loop*/
    for ( x = 0; x < 10; x++ ) {
        /* Keep in mind that the loop condition checks 
           the conditional statement before it loops again.
           consequently, when x equals 10 the loop breaks.
           x is updated before the condition is checked. */   
        printf( "%d\n", x );
    }
    getchar();
}

Example 5: While Loop

#include <stdio.h>

int main()
{
    int x;
    /* The loop goes while x < 10, and x increases by one every loop*/
    for ( x = 0; x < 10; x++ ) {
        /* Keep in mind that the loop condition checks 
           the conditional statement before it loops again.
           consequently, when x equals 10 the loop breaks.
           x is updated before the condition is checked. */   
        printf( "%d\n", x );
    }
    getchar();
}

Example 6: Do While Loop

#include <stdio.h>

int main()
{
  int x;

  x = 0;
  do {
    /* "Hello, world!" is printed at least one time
      even though the condition is false*/
    printf( "%d\n", x );
  } while ( x != 0 );
  getchar();
}