C

Archived

This page has been archived and will receive no further updates.

See:

General

Coding style

Google C++ Style Guide

Comments

/* This is a comment */

(No single-line comments, i.e. //)

Data types:

  • char
  • int
  • float
  • double

Notes:

  • C has no built-in data type for strings (only characters), so you can use an array of characters instead

  • C has no boolean data type. Use int (0 and 1) or see here:

    http://stackoverflow.com/a/1921557/399105

Variables

Declare a variable:

Note: variable declarations must come before other types of statements in the given code block!

type name

Ex:

int myVariable;
int a, b, c, d;

Declare a constant (variable that can only be assigned once):

const int x;

Pointers

  • Various uses:
    • To pass by reference instead of pass by value. This allows modification of the original object as well as can be less expensive than passing by value (which makes a copy of the object passed).
    • When a request to create an object on the heap is made, a pointer will be returned.
    • Arrays are pointers, as are strings (character arrays).
  • The pointer must be the same type as the variable it’s pointing to.

  • When declaring a pointer, these mean the same thing (use the first):

    int _p;
int_ p;

Referencing and dereferencing:

// int *p is used to declare a pointer variable that holds an address
void f(int *p) {
    // prints the address of the variable
    printf("%p\n", p);
    // prints the value of the variable. This is called dereferencing
    printf("%d\n", \*p);
...

int x = 47;
// use & in front of a variable to get the address of it (reference)
f(&x);

Structures

  • About as close as you get in C to an object; structures are types that can themselves contain a group of related types

Declare a struct:

struct Student {
    int grade1;
    int grade2;
};

(make sure you don’t forget to end it with a semicolon)

Declare a struct variable:

struct Student student1;

(treat it like a normal variable type except with the addition of struct)

Access a member of a struct:

student1.grade1 = 97;

Access a member of a struct pointer

struct Student \*sp = &student1; // define the pointer
cout << sp->grade1 << endl; // access a member of the struct pointer

Arrays

  • Ordered list containing elements of the same type
  • The size of the array must be declared beforehand
  • An array without brackets acts as a pointer (you don’t need to use the ampersand)

Declare an array:

type name[number_of_elements];

Ex:

int examplearray[100];

Declare a multidimensional array:

type name[number_of_elements][number_of_subelements];

Functions

  • Functions that do not return values have a return type of void
  • A prototype (declaring the function return type, name, arguments, and then ending with a semicolon) must be declared above main() if the function itself will be declared below#### Define a function:

return_type name (type arg1, type arg2, ...) { }

Ex:

int main()
{

(this is a function that returns an integer)

Declare a function with variable-lenth arguments:

Use an ellipsis as the last argument

Ex:

int some_function (int x, ...)
{
    va_list a_list;
    va_start(a_list, x);
}

Errors

C uses error constants like:

  • EINVAL: Invalid argument.
  • EPERM: Operation not permitted.

For more information, see: http://en.wikipedia.org/wiki/Errno

Misc

Display something to the screen

printf("text to display\n");

String formatting:

printf("You entered %d", this_is_a_number);

“static” modifier

  • When used inside a function to declare a variable, it simply means that once the variable has been initialized, it remains in memory until the end of the program
    • It also prevents that variable from being reinitialized if the function is called again (it retains its previous value)

Enums

Enums create named integers whose values are automatically assigned:

enum ShapeType {
    circle,
    square,
    rectangle
};
ShapeType shape = circle;