C Foundation

What is C? C Compiler Installation C Extensions C Compiler C Interpreter C Program Structure

C Basics

C Keywords C Data Types C Identifiers C Variables C Constant C Escape Sequences C Constant and Volatile C Typecast

Operators

What is Operator C Comma Operator C Arithmetic Operators C Relational Operators C Logical Operators C Bitwise Operators C Conditional Operators C : : Operator C Operator Priority

Basic IO's

Basic IO's C Formatted Functions C Unformatted Functions C Common Functions

Control Statements

What is Control Statement C if Statement C if else Statement C Nested if Statement C Else if Statement C Break Statement C Continue Statement C Switch Statement C Goto Statement

Looping

What is Control Loop C for Loop C Nested for Loop C while Loop C Nested while Loop C do while Loop C Nested do while loop

Functions

What is Function C User Defined Functions C Recursion C Passing Parameters

Scope

Scope C Local Scope C Global Scope

Storage Classes

What is Storage Class C Auto C Extern C Static C Register

Array

What is Array C One Dimensional Array C Two Dimensional Array C Multi Dimensional Array C Arrays Of Strings

String

What is String C String Functions

Pointer

What is Pointer C Pointers Arithmetic C Pointer to Pointer C Pointers and Arrays C Pointers and Strings C Pointer to Functions Void Pointers Null Pointers C Null and Void Pointer

Structure

What is Structure C Struct within Struct C Array within Structure C Pointer to Structure C Structure and Function C Enum C Bitfield Structure C Type def

Union

What is Union

Files

What is File C read a file C write a file C File Handling C Error Handling C Low Level Disk I/O C Other file functions

Memory Allocation

What is Memory Allocation C Malloc() C Calloc() C Free() C Realloc() C Coreleft()

C Reference

All ASCII Code Basic C Questions

C Interview

C Interview Sets All Star Patterns All Number Patterns All Alphabet Patterns All Series Patterns
The ones who are crazy enough to think they can change the world are the ones who do.
- Steve Jobs

C Prime Number

What Is Prime Number

A prime number is a whole number or a natural number greater than 1 that has no positive divisors other than 1 and itself. For example, 7 is prime number because it has no positive divisors other than 1 and 7. 6 is not a prime number because it has positive divisors such as 1, 2, 3, 6.

Prime Numbers From 1 to 100

prime numbers in c

Interesting Facts

  • 0 and 1 are not considered as a prime numbers.
  • 2 is the only even prime number.

C Program - Prime Number (Easy)

Let us work through a program to find whether the number is prime or not.

c-prime-number-1.c
#include <stdio.h>
int main()
{
int num, temp, i, j = 0;
printf("Enter a number to check if it is prime : ");
scanf("%d",&num);
for ( i = 2; i <= num/2; i++ )
{
temp = num%i;
if(temp == 0)
j++;
}
if(num > 1)
{
if ( j < 1)
printf("%d is a prime number",num);
else
printf("%d is not a prime number",num);
}
return 0;
}
Enter a number to check if it is a prime number: 111
111 is not a prime number

Note:

Logically prime numbers are divisible by 1 and by itself, so we have to neglect those numbers. Let us consider a prime number say 101, after half of this number i.e) 50.5 approx 50. only one number is cable of dividing 101 which is by itself. So we will consider the numbers from 2 to 50. Now the idea is straight forward, if any of those numbers from 2 to 50 will divide 101. Then clearly 101 is not a prime number. This is a logic we used in for loop condition.

C Program - Prime Number (Hard)

Let us work through a program to find whether the number is prime or not.

c-prime-number-2.c
#include <stdio.h>
int main()
{
int num, a;
printf("Enter a number to check if it is prime : ");
scanf("%d",&num);
for ( a = 2;a <= num-1;a++ )
{
if ( num%a == 0 )
{
printf("%d is not a prime number\n", num);
break;
}
}
if ( a == num )
printf("%d is a prime number",num);
return 0;
}
Enter a number to check if it is a prime number: 7
7 is a prime number

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