C Language CheatSheet

Basics

Basic syntax and functions from the C programming language.

Boilerplate Code

#include<stdio.h>
int main()
{
return(0);
}

printf function

It is used to show output on the screen

printf("Hello World!")

scanf function

It is used to take input from the user

scanf("placeholder", variables)

Comments

A comment is the code that is not executed by the compiler, and the programmer uses it to keep track of the code.

Single line comment

// It's a single line comment

Multi-line comment

/* It's a 
multi-line
comment
*/

Data types

The data type is the type of data

Character type

Typically a single octet(one byte). It is an integer type

char variable_name;

Integer type

The most natural size of integer for the machine

int variable_name;

Float type

A single-precision floating-point value

float variable_name;

Double type

A double-precision floating-point value

double variable_name;

Void type

Represents the absence of the type

void

Escape Sequences

It is a sequence of characters starting with a backslash, and it doesn't represent itself when used inside string literal.

Alarm or Beep

It produces a beep sound

\a

Backspace

It adds a backspace

\b

Form feed

\f

Newline

Newline Character

\n

Carriage return

\r

Tab

It gives a tab space

\t

Backslash

It adds a backslash

\\

Single quote

It adds a single quotation mark

\'

Question mark

It adds a question mark

\?

Octal No.

It represents the value of an octal number

\nnn

Hexadecimal No.

It represents the value of a hexadecimal number

\xhh

Null

The null character is usually used to terminate a string

\0

Conditional Instructions

Conditional statements are used to perform operations based on some condition.

If Statement

if (/* condition */)
{
/* code */
}

If-else Statement

if (/* condition */)
{
/* code */
}
else{
/* Code */
}

if else-if Statement

if (condition) {
// Statements;
}
else if (condition){
// Statements;
}
else{
// Statements
}

Switch Case Statement

It allows a variable to be tested for equality against a list of values (cases).

switch (expression) 
{
case constant-expression: 
statement1;
statement2;
break;
case constant-expression: 
statement;
break;
...
default: 
statement;
}

Iterative Statements

Iterative statements facilitate programmers to execute any block of code lines repeatedly and can be controlled as per conditions added by the programmer.

while Loop

It allows execution of statement inside the block of the loop until the condition of loop succeeds.

while (/* condition */)
{
/* code */
}

do-while loop

It is an exit controlled loop. It is very similar to the while loop with one difference, i.e., the body of the do-while loop is executed at least once even if the expression is false

do
{
/* code */
} while (/* condition */);

for loop

It is used to iterate the statements or a part of the program several times. It is frequently used to traverse the data structures like the array and linked list.

for (int i = 0; i < count; i++)
{
/* code */
}

Break Statement

break keyword inside the loop is used to terminate the loop

break;

Continue Statement

continue keyword skips the rest of the current iteration of the loop and returns to the starting point of the loop

continue;

Functions & Recursion

Functions are used to divide an extensive program into smaller pieces. It can be called multiple times to provide reusability and modularity to the C program.

Function Definition

return_type function_name(data_type parameter...){ 
//code to be executed 
}

Recursion

Recursion is when a function calls a copy of itself to work on a minor problem. And the function that calls itself is known as the Recursive function.

void recurse()
{
... .. ...
recurse();
... .. ...
}

Pointers

Pointer is a variable that contains the address of another variable,

Declaration

datatype *var_name;

Arrays

An array is a collection of data items of the same type.

Declaration

data_type array_name[array_size];

Accessing element

int variable_name = array[index];

Strings

A string is a 1-D character array terminated by a null character ('\0')

Declaration

char str_name[size];

gets() function

It allows you to enter multi-word string

gets("string");

puts() function

It is used to show string output

puts("string");

String Functions strlen()

It is used to calculate the length of the string

strlen(string_name);

strcpy() function

It is used to copy the content of second-string into the first string passed to it

strcpy(destination, source);

strcat() function

It is used to concatenate two strings

strcat(first_string, second_string);

strcmp() function

It is used to compare two strings

strcmp(first_string, second_string);

Structures

The structure is a collection of variables of different types under a single name. Defining structure means creating a new data type.

Structure syntax

struct structureName 
{
dataType member1;
dataType member2;
...
};

typedef keyword

typedef function allows users to provide alternative names for the primitive and user-defined data types.

typedef struct structureName 
{
dataType member1;
dataType member2;
...
}new_name;

File Handling

A set of methods for handling File IO (read/write/append) in C language

FILE pointer

FILE *filePointer;

Opening a file

It is used to open file in C.

filePointer = fopen(fileName.txt, w)

fscanf() function

It is used to read the content of file.

fscanf(FILE *stream, const char *format, ...)

fprintf() function

It is used to write content into the file.

fprintf(FILE *fptr, const char *str, ...);

fgetc() function

It reads a character from a file opened in read mode. It returns EOF on reaching the end of file.

fgetc(FILE *pointer);

fputc() function

It writes a character to a file opened in write mode

fputc(char, FILE *pointer);

Closing a file

It closes the file.

fclose(filePointer);

Dynamic Memory Allocation

A set of functions for dynamic memory allocation from the heap. These methods are used to use the dynamic memory which makes our C programs more efficient

malloc() function

Stands for 'Memory allocation' and reserves a block of memory with the given amount of bytes.

ptr = (castType*) malloc(size);

calloc() function

Stands for 'Contiguous allocation' and reserves n blocks of memory with the given amount of bytes.

ptr = (castType*)calloc(n, size);

free function

It is used to free the allocated memory.

free(ptr);

realloc() function

If the allocated memory is insufficient, then we can change the size of previously allocated memory using this function for efficiency purposes

ptr = realloc(ptr, x);