C Tutorial

C Tutorial C Language Environment Setup Execution flow of C program C printf and Scanf C Data type C Token Variable in C Operators in C Comments in C Escape Sequence in C C – Storage Classes C Decision control statement Loop Statement in C Break, continue and goto statement in C Type Casting in C Function in C Recursion in C String in C C Array Pointer in C Dynamic memory allocation C –Structure Nested Structure in C Union in C File Handling in C C pre-processor Static Function In C Sizeof In C Selection Sort In C Scope Of Variables In C Runtime Vs Compile Time In C Random Access Lseek In C Queue Implementation In C Pseudo Code In C Prototype In C Pointer To Pointer In C Pointer Arithmetic In C Passing Array To Function In C Null Character In C Merge Sort In C Macros In C Library Functions In C Memory Leak In C Int In C Goto And Labels In C Fibonacci Series In C Fflush In C Derived Data Types In C Data Types In C Const Vs Volatile In C Character Set In C Character Class Tests In C Calloc In C C Pointers Arrays In C Include In C Clrscr In C C Vs Java String Literals In C Types Of Pointers In C Variables In C Volatile In C Why C Is A Middle Level Language Infix To Postfix Program In C Ceil function in C LCM of two numbers in C Quick sort in C Static in C function pointer as argument in C Top Array Keywords in C Add two numbers using the function in C Armstrong program in C using function Array, Declaring Arrays and Array Initialization Limitations of Inline Function in C Merge and Merge sort with example in C Do-While Loop in C For Loop in C While-Loop in C Difference between while and do-while loop in C Array Of Structures in C Data Structures And Algorithms in C Types Of Structures In C How to Avoid Structure Padding in C Use of Structure in C Do WHILE LOOP in C Programming Examples For Loop in C Programming Examples Entry Control Loop in C Exit control loop in C Infinite loop in C Nested loop in C pow() function in C String Handling functions in C Prime Number code in C Factorial Program in C using For Loop Factorial Program in C Using While Loop Fibonacci Series in C Using For Loop Fibonacci series in C using while loop Prime Number Program in C using for Loop While Loop in C programming examples Built-in functions in C Assert() Function C vs Java Strings Call Back Function in Embedded C Else If Ladder fgets() function Ftell() Function getc() function getch() function gets() function Heap Sort Nested if-else statement Pi() Function Positioning of file Write() function abs() function in C Attributes in C C program to find factorial of a number using Recursion Ferror() in c fopen() function in C Fibonacci series program in C using Recursion Formatted Input and output function in C Snake Game in C User Defined Functions in C Beep() function in C Cbrt() function in C Hook() function in C Isalnum() function in C C Program to find the Roots of a Quadratic Equation C Switch Statements Difference between rand() and srand() function in C Difference between while and for loop in C Doubly Linked list in C Example of Iteration in C How to use atoi() function in C How to use floor() function in C How to use sine() function in C How to use Typedef Struct in C Integer Promotions in C C Program Swap Numbers in cyclic order Using Call by Reference C Program to Find Largest Number Using Dynamic Memory Allocation C Program to Find the Largest Number using Ternary Operator C/C++ Program to Find the Size of int, float, double and char Find the Largest Three Distinct Elements in an Array using C/C++ Loop Questions in C Modulus on Negative Numbers in C Multiplication table program in C using For loop Nested Loops in C Programming Examples C Program for Mean and Median of an Unsorted Array Results of Comparison Operations in C and C++ Reverse a Stack using Recursion in C Simple hash() function in C strcat() Function in C Sum of N numbers in C using For loop Use of free() function in C Write a program that produces different results in C and C++ C Function Argument and Return Values Keywords in C Bank management system in C Calendar application in C Floor() Function in C Free() Function in C How to delete a file in C How to move a text in C Remove an element from an array in C Unformatted input() and output() function in C What are linker and loader in C SJF Scheduling Program in C Socket Programming in C Structure in C Tower of Hanoi in C Union Program in C Variable Declaration in C What is Linked List in C While Loop Syntax in C fork() in C GCD program in C Branching Statements in C Comma Operator in C Control statement in C Double Specifier in C How to create a binary file in C Long int in C Palindrome Number in C Pure Virtual Function in C Run Time Polymorphism in C Types of Array in C Types of Function in C What is a buffer in C What is required in each C Program Associativity of Operators in C Bit Stuffing Program in C Actual and Formal Parameters Addition of two Numbers in C Advantages of function in C Arithmetic Progression Program in C Binomial Coefficient Program in C Difference between Array and List in C Diffie-Hellman Algorithm in C How to convert a number to words in C How to convert a string to hexadecimal in C Difference between If and Switch Statement in C C and C++ Binary Files C program that does not Suspend when Ctrl+Z is Pressed Different ways to Declare the Variable as Constant in C Range of Int in C C Program to find the size of a File FIFO Example in the C Language For loop in C Programming GCD program of two numbers in C GPA Calculator in C How to Calculate Time Complexity in C How to include graphics.h in C How to measure time taken by a function in C How to return a Pointer from a Function in C What is the main in C Addition of Matrix in C Booleans in C C Program for Extended Euclidean algorithms C Program of Fencing the Ground Ceil and Floor in C Compound Interest Program in C Displaying Array in C Distance Vector Routing Protocol Program in c Dos.h Header File in C Language DSA Program in C Explain the two-way selection in C Fee Management System in C File Operations in C

Simple hash() function in C


In this context, we briefly discuss HASH FUNCTION, HASHING or HASH TABLE in C. It is a function used to map data and mapped arbitrary sizes to the fixed-size values.

The most crucial topic in hashing is “SEARCHING”, which determines the time complexity. It reduce time complexity. The data is stored in the array format in the

Simple hash function in C

hash table. It is a faster technique and also very useful. This table held the data in an associative manner.

In this above diagram, we have seen that the actual data is to be stored in the hash key. The key value goes to the hash function. The hash function moved towards the hash value.

The hash value stored in the hash table.

By this diagram we can see that how hash function is works in C language.

What is Hash Function?

In the hash function, H accepted a variable-length block of input known as M and produced the fixed size of the hash value. That value is represented as:                                               

 h = H (M)

The Hash function uses the operation of the constant time. The function is converted a significant number into a small integer form. This function is to store values. It is also used to recover the values from the hash table. This is also used as the address in the hash table.

What are the 3 main properties of the HASH FUNCTION ?

There are three main properties of the secure hash function: Pre-image resistance, Second pre-image resistance, and collision resistance.

What is meant by the good hash function in C ?

A hash function should have the following properties. This properties is determine whether the function is good or bad. The properties are :

  1. In this function, Keys are should be uniformly distributed.
  2. The efficiency of this function should be computable.

Why we use the hash function?

The Hash function uses to store the values. It reduces values from a database because it helps accelerate the process.

Types of hash function in C

The types of hash function in C language are :

  1. Division Method
  2. Mid Square Method
  3. Digit Folding Method
  4. Multiplication Method

Now we are briefly discuss in these method :

1.Division Method :  This method is the most accessible and straightforward method to generate the hash value. The hash function depends upon the reminder of a division; if the hash function divides the value X by M, then the remainder is obtained.

Formula of direct method:

h (x) = x mod M


x is the value of key

M is the size of the hash table

M is the prime number because it is decided that the keys value are uniformly distributed.

Example :

If the value,
x = 1234
M = 4
h (1234) = 1234 mod 4

Advantage :

  • This method is a speedy operation.
  • This method requires only a single division operation and is suitable for the value M.

Disadvantage :

  • We need to take extra care in choosing the value M.
  • The division method leads to poor performance.

2. Mid Square Method : In the mid-square method, the middle part of the square element takes as the index. It is a perfect and valuable hashing method. In this method, two steps require to compare the hash value. The steps are:

Square the value of the key. Which means X2. Exact the middle r digit as the hash value. The value of the r is to be decided based on the size of the table value.

Formula :

h (X) = h (X * X)

here , X is the key value .

Example :

X = 50
X * X = 50 * 50
h (X) = h (X * X)
h (50) = 50
\The hash value is 6

Advantage :

  • In this method, the result is not dominated by the distribution of the top or bottom digit of the main key value.
  • The performance is good in this method.

Disadvantage :

  • In this method, if the size of the key is significant, then its square will double the number of digits.
  • In the mod square method, there is a collision present.

3. Digit Folding Method : The digit folding method is done in two steps:

In this method, the value of key or critical X divides into several parts that are X1, X2, X3, X4………Xn.

Each part contains the same number of digits except the last part because it contains less number of digits than the other part. Then, each part is added, and the hash value we find by ignoring the last carry.

Formula :

X = the key value
X = X1 ,X2, X3, X4 ……… Xn
Sum = X1 + X2 + X3 + X4 + ……… + Xn
h(X) = Sum


Sum is find by adding the parts of key X.

Example :

X = 170316
X1 = 17 ,X2 = 03, X3 = 16
Sum = X1 + X2 + X3
h (X) = 36

4. Multiplication Method : The multiplication method is done by following steps At first, choose a value Y. The value of Y is 0<Y<1.

The key value is X.

Multiply X with Y and extract the functional part from XY.

Then multiply the value of XY with the value of hash table M. The hash value finds by taking the resulting floor in step (iii).

Formula :

h (X) = floor (M(XY mod 1 ))


  • X is the Key value
  • K is the choose value or constant value
  • M is the size or value of the hash table

Example :

X = 1256
Y = 0.523
M = 10
h (1256) = floor (10(1256 * 0.523 mod 1))
= floor (10(656.888 mod 1))
= floor (10(0.888))
= floor (8.88)
= 8

Advantage: The multiplication method is easy to use. This method can work at any value between 0 to 1. The user can easily understand this method.

Disadvantage: The multiplication method depends on the size of the table value. The table value should be in the power of the two, which means table value = 2n [n = 1, 2, 3 …..].Then the whole process of computing the index using hashing value is too fast.

Collision resolution Technique : Collision is storage or condition when two or more data items arrive in the exact location. The collision resolution techniques are mainly two types.

 The techniques are :

  1. Chaining - This is also known as Open hashing.
  2. Open addressing – This is also known as Close hashing.

We want to make an external chain. This technique is also known as open hashing because the provided space, and open space, are used in this hashing. This method gives some chains or boxes for the record that needs two-element entries.

Example – 24, 19, 32, 44, 51 with the hash table size 6

Hash (key) = 24 % 6 = 0

Hash (key) = 19 % 6 = 1

Hash (key) = 32 % 6 = 2

Hash (key) = 44 % 6 = 2

Hash (key) = 51 % 6 = 3


Table no two is already packed with the data 32; that’s why a chain connects 44 in table 2. This is the method of chaining.

Open Addressing : Open addressing means the provided space in the hash table utilizes first. This is also known as closed hashing. Open addressing is divided into three parts – (i) Linear Probing, (ii) Quadratic Probing, and (iii) Double Hashing.

1.Linear Probing –

The Linear Probing method is another technique for collision resolution. In this method, we don’t space the 2 data in one table. By this method, we placed the second data in the following empty table or the space. But if no open space is founded, then it leads to clustering. Then this problem is also known as the clustering problem.

Example - 24, 19, 32, 44 with the hash table size 6

Hash (key) = 24 % 6 = 0

Hash (key) = 19 % 6 = 1

Hash (key) = 32 % 6 = 2

Hash (key) = 44 % 6 = 2


In this diagram, the data 32 and 44 are wanted to place in table no 2, but this method doesn’t allow it. So 32 set table no 2 and 44 sets next empty space, i.e. table no 3.

2.Quadratic Probing –

This method is used to solve the problem which is arrived at by linear probing. The Quadratic Probing method resolves the problem of clustering. The hash function with the hash key is calculated as :

hash (key) = (hash (key) +x*x ) % (size of the hash table)

[x = 1, 2, 3, 4,…….]

Example –24, 19, 32, 44 with the hash table size 6

Hash (key) = 24 % 6 = 0

Hash (key) = 19 % 6 = 1

Hash (key) = 32 % 6 = 2

Hash (key) = 44 % 6 = 2


This diagram shows that 24, 19 and 32 are easily placed in the hash table. But in the case of 44, it has the same hash key value as 32. So as per this method, we calculate the Hash key value of 44.

hash (44) = (44+ (1*1)) % 6 = 3

 so the hash key value of 44 is 3. Now we placed 44 in index number 3.

Double Hashing –

Double means two hash functions we can use here. Using two hash functions, we can resolve the collision problem. Two steps do this method : Calculated just using a simple division method. This must not be equal to zero, and entries must be probed.                      

Hash (key)1 = Key % size of the hash table

Hash (key)2 = p – (key mod p) [p is Prime Number  < size of the hash table]

Example – 20, 34, 45, 70 with table size 11

Hash (key) = 20 % 11 = 9

Hash (key) = 34 % 11 = 1

Hash (key) = 45 % 11 = 1

Hash (key) = 70 % 11 = 4


R1(k) = k mod 11

R2(k) = 8 – ( k mod 8 )

In this diagram , the element 45 can be placed using hash 2(key) = 8 – (45 % 8) = 3

(R1(k) + R2(k)) mod 11

= 1 + 1*3  = 4

So, we place the element 45 in table number 4. Now the hash key value of 70 is 4 . But 45 is already stored in to table number 4 . The element 70 can be placed using hash2(key) = 8 – (70 % 8) = 2

 (R1(k) + R2(k)) mod 11

= 4 + 2 = 6

So, we place the element 70 in table number 6.     

Application of HASH FUNCTION

The hash function is used in programming languages like C, C++, Python, and Java script to implement objects. It is also used in disk-based data structure and database indexing. Hash is used in cryptography and password verification.

Advantage of HASH FUNCTION

The Hash function is more efficient and provides better synchronization than the data structure. It gives a time constant for searching, deletion, and insertion.

Disadvantage of HASH FUNCTION

Main disadvantage of the hash function is a collision. The Hash function also does not allow the null values.


Hashing is very efficient and effective for searching the data. It is a fast method. The hashing is better than any data structure.