Hello Developers ! Today I'm starting cheatsheet Series. I'll be posting cheatsheet for programming languages and many more.

These cheatsheets are also available on my GitHub.
Improve this GitHub repository by contributing to it

Download PDF from here

C Cheatsheet

Table of content

• C Cheatsheet
  • Table of content
  • Boilerplate Code
  • printf() function
  • scanf() function
  • Variables
  • Basic Data Types
  • Format Specifiers
  • Escape Sequences
  • Operators
  • Conditional Statements
    • If Statement
    • If-Else Statements
    • If Else-If Statements
    • Switch Case Statements
    • Iterative Statements
    • While loop
    • Do-While Loop
    • For Loop
    • Break Statement
    • Continue Statement
  • Functions
  • Recursion
  • Pointers
  • Arrays
  • Strings
    • Important String Functions
  • Structures
  • Dynamic Memory Allocation
  • File Handling
• Credits

Boilerplate Code

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

printf() function

It is used to print anything/show output on console

printf("Hello World");

scanf() function

It is used to take input from user

scanf("format specifier",variable_name);

Variables

It is data name that is used to store the data value in the memory.

Rules to declare variables:

Basic Data Types

char - It stores single character. Size - 1 byte

char var_name = 'a';
// Another example
char var_name2 = 'x';

int - It stores an integer value. Size - 4 bytes

int age = 18;
//Another example
int amount = 10000;

float - It stores an floating point value with 6 digit precision. Size - 4 bytes

float radius = 5.8;
//Another example
float area = 15.2;

double - It stores an float value with 14 digit precision. Size - 8 bytes.

double var = 12.1531452;
//Another Example
double more_var = 542.12452;

void - Represents the absence of type.

void main(){
    //does not return anything.
}

Format Specifiers

Escape Sequences

Operators

Arithmetic Operators

Relational Operators

Logical Operators

Increment and Decrement Operators

variable_name++ Here ++ is a increment operator, it increments the value of variable by 1.
variable_name-- Here -- is a decrement operator and it decrements the value of variable by 1.

More examples:

int a = 1; // a value is 1
a++;       // Now Value becomes 2

int b = 5; // b value is 5
b--;       // Now, b value is 4

Conditional Statements

If Statement

if(codition)
{
    //statements or code
}
//example
int a = 1, b = 5;
if(a < b){
    printf("A is smaller");
}

If-Else Statements

if(condition){
    //statements
}
else{
    //statements
}
//example
int a=1; b=5;
if(a < b){
    printf("A is smaller");
}
else{
    printf("B is smaller");
}

If Else-If Statements

if(condtion){
    //code
}
else if(another_condtion){
    //code
}
else{
    //code
}

Switch Case Statements

switch(expression)
{
    case constant-expression:
        statement1;
        statements2;
        break;
    case constant-expression:
        another_statements;
        break;

    .....(n number of cases)
    default;
        statements;
}

Iterative Statements

It executes the statements inside a block of loop until condition is false

While loop

while(condition){

    //code
}
//example

int a = 10;
while(a <=10){
    printf("%d",a);
}//will print 1 to 10

Do-While Loop

do{
    // code
}
while(codition);

For Loop

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

Break Statement

Break keyword is used to terminate the loop.

break;

Continue Statement

Continue keyword skips the rest of iterative code of loop and return to starting point of loop.

continue;

Functions

Functions are used to divide the code and to avoid repetitive task. It provides reusability and readability to code.
Function Declaration

return_type function_name(data_type-parameters){
    //code
}
//  Example of function to add two numbers

int add(int a, int b){
    return a+b;
}

Recursion

Recursion is the process of repeating items in a self-similar way.If a program allows you to call a function inside the same function, then it is called a recursive call of the function.

void myFunction(){
    myFunction();   //Function calling itself
}

//Factorial Using Recursion
long factorial(long n){
    if(n==0){
        return 1;
    }
    return n * factorial(n -1);
}

int main(){
    int n = 5;
    printf("Factorial of %d is %l.",n,factorial(n));
    return 0;
}
//OUTPUT : Factorial of 5 is 120.

Pointers

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

datatype *var_name;

Arrays

Array is an collection of data of same data-type.

Declaration

data_type array_name[array_size];

Fetching Array Element
Array index starts from 0.

data_type variable_name = arr[index]

//Example

int arr = {1,2,3,4,5};
printf("%d",arr[0])
//OUTPUT : 1

Strings

It is basically 1D character array. It character of string is null character (\0)
Declaration

char string_name[size];

Important String Functions

gets() function
It is used to take input of multi-character string

gets("string");

puts() function
It is used to show string output

puts("string");

strlen() function
It prints the length of string.

strlen(string_name);

strcat() function
It is used to concatenate two strings.

strcat(string1, string2);

strcmp() function
It is used to compare two strings. Gives output in 0/1.

strcmp(string1, string2);

strcpy() function
It is used to copy the content of 1st string to another string.

strcpy(string1, string2);

Structures

A structure creates a data type that can be used to group items of possibly different types into a single type.
Declaration

struct student
{
    char name[50];
    int class;
    float percentage;
    char college[50];
};      //Notice the semicolon

Dynamic Memory Allocation

If you are aware of the size of an array, then it is easy and you can define it as an array. For example, to store a name of any person, it can go up to a maximum of 100 characters. But now let us consider a situation where you have no idea about the length of the text you need to store, for example, you want to store a detailed description about a topic. Here we need to define a pointer to character without defining how much memory is required and later. So we use Dynamic Memory Allocation.

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

var = (casting_type*)malloc(size);
//Example
var = (int*)malloc(n * sizeof(int))

calloc() function
Stands for “contiguous allocation” method in C is used to dynamically allocate the specified number of blocks of memory of the specified type.

var = (cast_type*)calloc(n, size);

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

var = realloc(var2,n);

File Handling

Creating File Pointer

FILE *file

Opening a File

file = fopen(file_name.txt,w)

fscanf() function
Used to read file content

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

fprintf() function
Used to write the file content

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

Closing a File

fclose(file);

Credits

This cheatsheet is written and managed by Rohan Kiratsata.

Something is missing? Contribute to this repo and improve.