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C Programming Language Basics Cheat Sheet (DRAFT) by

This has the basics involved in the C Programming Language

This is a draft cheat sheet. It is a work in progress and is not finished yet.

General Knowledge

Syntax in C
All Statements in C must end with a semicolon ;
keywords and other code elements are case-s­ens­itive
Escape Sequences
In C, within a string the \n will cut the string and move the part after to the next line. The \t will tab the string after, giving it more space
Single Line Comments
//This is a single line comment within c
Block Comments
/* Block comments are nice for when you have a lot to say about a particular piece of code */
Compiling C Code
to compile c code, in a terminal you'll need to type in, minimally, gcc fileName.c
this will output something call a.out which will allow you to run the program
Altern­ati­vely, if you do gcc fileName.c -o fileName you can then run it using the denotation of filename instead


if Statements
if(x == 3){
else-if Statements
if(x == 3){
} else if (x < 3) {
printf(x - 1);
else statements
if(x == 3){
} else if (x < 3) {
printf(x - 1);
} else {
Ternary Operators: A condensed if-else statement
if (a < b) {
min = a;
} else {
min = b;

min = a < b ? a : b; ((This is the ternary Operator for the above if)
to briefly explain it, it essent­ially will set min to a if the a < b is true otherwise b, the second option, will be what min is set to
Switch Statem­ents: A Condensed series of cascading else statem­ents, it tests a value and compares it against multiple cases.
switch (grade) {
case 9:


Functions in C
A function is a block of reusable logic that may have a defined set of input and output
Built-In Function in C
The C Progra­mming language comes with built-in standard library fuctions
- printf()
**Note to be able to use these make sure to #include <st­dio.h>
Calling Functions
int myNumber = increm­ent­By(5, 2);

A function is called by stating the function name followed by parent­heses. One or more argument values can be places in the parent­heses as the function requires.
Storing a return value
int myNumber = increm­ent­By(5, 2);

A function's return value, or output, can be stored in a variable for future use.
Function Signature
Return Type


Variable Names in C
In C, Variable names follow specific Rules:
Names can only be composed of upper and lower case letters, numbers, and unders­cores.
The first character must be a letter (upper or lower case).
No keywords are allowed as the full name (int is not allowed but int_count would work)
Data Types in C
The four main data types in c are: int, char, double, and float
Declaring Variables in C
int int_count = 4;
double priceA­pples;
Setting Variables in C
When you declare a variable, you do not need to set it right away, but you can set it right away if you want to
Variable Casting in C
You can implicitly or explicitly cast to variables in C. However, implicitly casting may not have the same effect as explicitly casting

Loops and Errors

While Loops, will iteratre until a condition is met
while (a < 10) {
do -While loops, while loops that initially execute the body once before checking conditions
do {
printf­("not true!");
} (while 2 == 3);
for loops, iterates a set number of times
for (int i = 0; i <= 10; i++) {
Loop Keywords
All Loops can Utilize Keywords like continue and break.
Continue will restart the loop without completing anything within the loop past the continue keyword.
break will completely stop the loop and continue on after it within the code.

Pointers and Memory

What is a pointer?
A pointer is a variable that sotres the hexade­cimal address of the variable it is pointing to within memory
Declaring pointers
type* pntr;
type *pntr;
Accessing Memory Address
A Memory Address of a vairiable is obtained using the reference operator (&).
*example &var
Derefe­rencing Pointers
A Pointer is derefe­rence using the derefe­rence operator (*)
*Example *pntr
Increm­enting and Decrem­enting Pointers
Pointers can be increm­ented and decrem­ented using the + and - arithmetic operators
Accessing Arrays
Arrays can be accessed by using a pointer to the first element and icreme­nting and decrem­enting as necessary


Mathma­tical Symbols in C
Addition: +
Subtra­ction: -
Division: /
Multip­lic­ation: *
Increm­enting: ++
Decrem­enting: --
Modulo: %
Assignment Operations in C
Assign­ment: =
Addition then Assign­ment: +=
Subtra­ction then Assign­ment: -=
Multip­lic­ation then Assign­ment: *=
Division then Assign­ment: /=
Modulo then Assign­ment: %=
Comparing Values in C
Both sides Equal?: ==
Two sides not equal?: !=
left lower then right?: <
left lower or equal to right?: <=
left greater than right?: >
left greater than or equal to right?: >=
Logical Operators in C
and: && (Both sides true?)
or: || (At least one side true?)
not: ! (true = false, false = true)

Arrays and Strings

Creating Uninit­ialized Arrays
type arr[ar­ray­_size];
char word[15];
Creating initilized Arrays
type arr[] = {el1, el2};
char word[] = {'H', 'e', 'l, 'l', 'o', '\0'}
Accessing Array Elements
word[0]; ('H')
First and Last Array Elements
firstE­lement = arr[0];
lastEl­ement = arr[ar­raySize - 1];
Note C does not have a built in way to actually find the size of an array, this is simply a handy trick to find the amount of elements an array should be able to hold.
int arr[17];
size_t sizeArr = sizeof­(arr) / sizeof­(ar­r[0]);
**Note size_t is an unsigned integer type used to represent the size of objects in bytes, its the return type of sizeof()
Invalid Array Access
While it is possible to access beyond an array, it will cause the program to behave unpred­ictably
Creating Multid­ime­nsional Arrays
unitia­liz­edM­ultArr = type arr[12­][1­5]...[13];
initia­liz­edM­ultArr = type arr[][­15]­[20­]...[n] = {{elm1, elm2}, {elm3}}
Arrays are static
The length of a string cannot be modified as a string is a char array in C
Null Character
All Strings terminate with a null character ('\0')
The length of a string
find the length using the strlen() function
string concat­enation
strcat() function can be used to concate two strings
a string can be copied into an empty char array using this function