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====== C versus C++ ======
Mithat Konar \\ 
Derived from //**Differences Between C and C++**// by Robert Niemann \\
2020-05-03

===== Different header files =====
  * ''<stdio.h>'' input/output
  * ''<stdlib.h>'' standard utility functions
  * ''<string.h>'' string operations
  * ''<ctype.h>'' character class tests
  * ''<math.h>'' math functions

===== Input and output =====
  * C's console and file I/O initially seems more complicated than C++.
  * But it's sometimes preferable even in C++.

===== Console I/O =====
  * ''printf()'' write a formatted string to the console 
  * ''scanf()'' read a formatted string from the keyboard
  * ''putchar()'' write a single character to the console
  * ''getchar()'' read a single character from the keyboard
  * ''puts()'' write a string to the console
  * ''gets()''  read a string from the keyboard

===== File I/O =====
  * Works with pointers to type ''FILE'':<code c>FILE *fp;  /* create a pointer to FILE */</code>
  * ''fopen()'', ''fclose()'' open/close a text file.
  * ''feof()'' detect end-of-file marker in a file.
  * ''fscanf()'' read formatted string from a file.
  * ''fprintf()'' write formatted string to a file.
  * ''fgets()'', ''fputs()'' read/write a string.
  * ''fgetc()'', ''fputc()'' read/write a single character.

===== C is not object-oriented =====
  * You can't create classes or objects in C.
  * You can't use any of C++'s predefined classes and objects.
  * So, no
    * ''cout''
    * ''cin''
    * ''string''
    * ''class''
    * etc.

===== C does not have =====
  * boolean type
    * use ''int'' instead
  * reference variables and function parameters
    * use pointers instead
  * function overloading
    * use clever naming instead
  * ''%%//%% single line comments'' (in older versions of C)
    * use ''/* multi-line syntax */'' instead

===== Strings =====
<code c>
#include <string.h>       /* needed to use strlen() function */

int main(void) {
  char s1[81] = {'H', 'e', 'l', 'l', 'o', '\0'};
  char s2[81] = "Hello World";
  char s3[] = "O hai.";

  int len1 = strlen(s1),  /*  5 */
      len2 = strlen(s2),  /* 11 */
      len3 = strlen(s3);  /*  6 */
  
  ...
</code>
  * Use null-terminated character arrays.
  * Use functions in ''[[https://pubs.opengroup.org/onlinepubs/009695399/basedefs/string.h.html|string.h]]'' to operate on strings.
    * C's ''[[https://pubs.opengroup.org/onlinepubs/009695399/basedefs/string.h.html|string.h]]'' and C++'s ''[[http://www.cplusplus.com/reference/cstring/|cstring]]'' are essentially duplicates.
===== Defining variables =====
<code c>
int  main( )
{
    int a,b,c;
    float x,y,z;
    
    ...
}
</code>
  * In older versions of C, you must define all variables at the beginning of a function.
  * Common practice today anyway.
===== Prototypes =====
<code c>
/* int foo(); <--optional */

int main()
{
    foo();
    return 0;
}

int foo()
{
    printf( "Hello world" );
}
</code>

  * Function prototypes are not required.
  * Best practice to use them anyway.
===== Named constants and macros =====
  * ''const'' modifier is available only in newer versions of C.
  * ''#define'' preprocessor directive typically used instead.<code c>
#define PI 3.1415
#define TAX_RATE 0.065
</code>
  * ''#define'' also often used to create function-like //macros//.<code c>
#define square(x) ((x) * (x))
</code>

===== Casting =====
<code c>
int myInt = 42;
double myDouble;

myDouble = (double)myInt/3;  /* cast myInt to a double */
</code>
  * Place the type you want a value cast to inside parenthesis before the value.
  * No ''static_cast<>'', etc.

===== Dynamic memory =====
  * Use ''malloc()'' and ''free()''.

  * Allocating memory:<code c>
int *x = (int *) malloc(sizeof(int));          /* a single int */
int *xArry = (int *) malloc(sizeof(int) * 10); /* array of ints */
</code>

  * Deallocating memory:<code c>
free(x);
free(xArry);
</code>

===== Structs =====
<code c>
struct MyStruct
{
    double x;
    double y;
};

struct MyStruct aStructInstance;  /* requires struct keyword */
</code>
  * Only member variables are allowed.
    * No member functions.
  * Everything is public.
    * No access specifiers.
  * You must use the ''struct'' keyword when defining ''struct'' variables.



===== Classes =====
  * Nope. Nada. Epic fail. No classes or objects in C //at all//.
===== Some C Resources =====

  * [[https://www.math.brown.edu/~jhs/ReferenceCards/CRefCard.v2.2.pdf|C Reference Card (ANSI)]] Highly recommended!
  * [[C examples|C code examples]]