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C info and some basic characteristics Cheat Sheet by

This is a Cheatsheet about C and its basic characteristics

C Cheat sheet

Basic Types
Arithmetic types and are further classified into: (a) integer types and (b) floati­ng-­point types.
Enumerated types
Arithmetic types and they are used to define variables that can only assign certain discrete integer values throughout the program.
The type void
Type specifier void indicates that no value is available.
Derived types
Include (a) Pointer types, (b) Array types, (c) Structure types, (d) Union types and (e) Function types.

Data types

Integer Types
Storage size
Value range
1 byte
-128 to 127 or 0 to 255
unsigned char
1 byte
0 to 255
signed char
1 byte
-128 to 127
2 or 4 bytes
-32,768 to 32,767 or -2,147­,48­3,648 to 2,147,­483,647
%d or %i
unsigned int
2 or 4 bytes
0 to 65,535 or 0 to 4,294,­967,295
2 bytes
-32,768 to 32,767
unsigned short
2 bytes
0 to 65,535
8 bytes
-92233­720­368­547­75808 to 922337­203­685­4775807
unsigned long
8 bytes
0 to 184467440737095516
Floati­ng-­Point Types
Storage size
Value range
4 byte
1.2E-38 to 3.4E+38 (6DP)
8 byte
2.3E-308 to 1.7E+308 (15DP)
long double
10 byte
3.4E-4932 to 1.1E+4932 (19DP)
x50 char
* DP = Decimal precision.


Equal to
Non equal to
Arithmetic Operators
++/ --
lower than
lower or equal than
greater or equal than
greater than

Main Libraries and Functions

Program assertion functions
Character type functions
Locali­zation functions
Mathem­atics functions
Jump functions
Signal handling functions
Variable arguments handling functions
Standard Input/­Output functions
Standard Utility functions
String handling functions
Date time functions
std functions:
Returns a (predi­ctable) random integer between 0 and RAND_MAX based on the randomizer seed.
The maximum value rand() can generate.
srand(­uns­igned integer);
Seeds the randomizer with a positive integer.
(unsigned) time(NULL)
Returns the computer's tick-tock value. Updates every second.

i/o functions

scanf() and printf() functions
printf( )
returns the number of characters printed by it.
returns the number of characters read by it.
getchar() & putchar() functions
reads a character from the terminal and returns it as an integer.
displays the character passed to it on the screen and returns the same character.
gets() & puts() functions
reads a line from stdin(standard input) into the buffer pointed to by str pointer, until either a termin­ating newline or EOF (end of file) occurs.
writes the string str and a trailing newline to stdout.
The standard input-­output header file, named stdio.h contains the definition of the functions printf() and scanf(), which are used to display output on screen and to take input from user respec­tively.

ontrol structures and statements

Loop structure

A loop structure is used to execute a certain set of actions for a predefined number of times or until a particular condition is satisfied. There are 3 control statements available in C to implement loop struct­ures. While, Do while and For statem­ents.

The while statement
Syntax for while loop is shown below:

while(­con­dition)// This condition is tested for TRUE or FALSE. Statements inside curly braces are executed as long as condition is TRUE
statement 1;
statement 2;
statement 3;

The condition is checked for TRUE first. If it is TRUE then all statements inside curly braces are executed. Then program control comes back to check the condition has changed or to check if it is still TRUE. The statements inside braces are executed repeat­edly, as long as the condition is TRUE. When the condition turns FALSE, program control exits from while loop.

The do while statement
Syntax for do while loop is shown below:

statement 1;
statement 2;
statement 3;

The for statement
Syntax of for statement is shown below:

for(in­iti­ali­zation statem­ent­s;test condit­ion­;it­eration statem­ents)
statement 1;
statement 2;
statement 3;

Control structures

Selective control structure
Selection structures are used to perform ‘decision making‘ and then branch the program flow based on the outcome of decision making. Selection structures are implem­ented in C with If, If Else and Switch statem­ents.

The syntax format of a simple if statement is as shown below.

if (expre­ssion) // This expression is evaluated. If expression is TRUE statements inside the braces will be executed
statement 1;
statement 2;
statement 1; // Program control is transfered directly to this line, if the expression is FALSE
statement 2;

Syntax format for If Else statement is shown below.

if(exp­ression 1) // Expression 1 is evaluated. If TRUE, statements inside the curly braces are executed.
{ // If FALSE program control is transf­erred to immediate else if statement.

statement 1;
statement 2;
else if(exp­ression 2)// If expression 1 is FALSE, expression 2 is evaluated.
statement 1;
statement 2;
else if(exp­ression 3) // If expression 2 is FALSE, expression 3 is evaluated
statement 1;
statement 2;
else // If all expres­sions (1, 2 and 3) are FALSE, the statements that follow this else (inside curly braces) is executed.
statement 1;
statement 2;
other statem­ents;

Switch statement

Switch is a multi branching control statement. Syntax for switch statement is shown below.

switch­(ex­pre­ssion)// Expression is evaluated. The outcome of the expression should be an integer or a character constant
case value1: // case is the keyword used to match the intege­r/c­har­acter constant from expres­sion.
//value1, value2 ... are different possible values that can come in expression
statement 1;
statement 2;
break; // break is a keyword used to break the program control from switch block.
case value2:
statement 1;
statement 2;
default: // default is a keyword used to execute a set of statements inside switch, if no case values match the expression value.
statement 1;
statement 2;


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