Program of Prime Number with explanation | In C

Practice Program

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Program of prime Number.

A prime number is a natural number greater than 1 that has no positive integer         divisors other   than 1 and itself.

 For example, 5 is a prime number because it has no positive divisors other than 1 and 5.

Solution: through for loop

void main()
{
    int i,j,n;
    printf("Enter the number:");
    scanf("%d",&n);
    
     printf("Prime numbes from 1 to %d are:\n",n));
    for(j=1;j<=n;j++)
    {

        for(i=2;i<i++) //for every value of j we are checking
        {               //the divisibility of that number with 2 to (j-1)
            if(j%i == 0)
            {         //if j value  is divisible by i value then
              break;   //we are terminating the loop with the break keyword

            }           //termination is the indication
                       //that given number is not an prime number

        }//As above loop will complete normally,means it will not get terminated by break keyword
        if(j == i)        //then value of j will become equal to the value of i
           printf("%d\t",j);      //being both the value equal is the indication that the number is a Prime number,
                            //so we are checking that values are equal or not
                            // if they are equal then we are printing it


}


}

Output1

Enter the number:20

Prime numbers from 1 to 20 are: 2       3        5        7        11     13    17    19

Output2

Enter the number:10

Prime numbers from 1 to 10 are:
2       3        5        7

Output3

Enter the number:30

Prime numbers from 1 to 10 are:
2       3        5        7        11     13    17    19    21    23    27    29

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Solution: from while loops

void main()
{
    int i,j,n;
    printf("Enter the number:");
    scanf("%d",&n);
    j = 1;
    printf("Prime numbers from 1 to %d are:",n);
    while(j<=n)
    {
        i=2;
        while(i<j) //for every value of j we are checking
        {               //the divisibility of that number with 2 to (j-1)
            if(j%i == 0)
            {         //if j value  is divisible by i value then
              break;   //we are terminating the loop with the break keyword

            }           //termination is the indication
                       //that given number is not an prime number
         i++;
        }//As above loop will complete normally,means it will not get terminated by break keyword
        if(j == i)        //then value of j will become equal to the value of i
           printf("%d\t",j);      //being both the value equal is the indication that the number is a Prime number,
                            //so we are checking that values are equal or not
                            // if they are equal then we are printing it

     j++;
}


}

Solution: from do-while loops

void main()
{
    int i,j,n;
    printf("Enter the number:");
    scanf("%d",&n);
    j = 1;
    printf("Prime numbers from 1 to %d are:",n);
    do
    {
        i=2;
        do//for every value of j we are checking
        {               //the divisibility of that number with 2 to (j-1)
            if(j%i == 0)
            {         //if j value  is divisible by i value then
              break;   //we are terminating the loop with the break keyword

            }           //termination is the indication
                       //that given number is not an prime number
         i++;
        } while(i<j);//As above loop will complete normally,means it will not get terminated by break keyword
        if(j == i)        //then value of j will become equal to the value of i
           printf("%d\t",j);      //being both the value equal is the indication that the number is a Prime number,
                            //so we are checking that values are equal or not
                            // if they are equal then we are printing it

     j++;
}while(j<=n);


}

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defining a function 'is_prime' which will check whether a number is prime number or not.

int is_prime(int n)
{
    int i,raise;

    for(i=2;i<i++)
    {
        if(n%i == 0)
        {
            raise = 1;
            break;
        }
    }
    if(n == i)
    {
        return 1;
    }
    else
        return 0;

}

Using above define function 'is_prime()':

void main()

{
    int n,result;

    printf("Enter the Number");
    scanf("%d",&n);

    //calling function.
    result = is_prime(n);//actual parameter.

    if(result == 1)//if 'is_prime()' will return 1,
    {            // then number is prime,otherwise not
        printf(Prime Number);
    }
    else
        printf("Not an Prime Number");
}

Output1

Enter the Number:407

Prime Number

Using above define function 'is_prime()':

void main()

{
    int n,result;

    printf("Enter the Number");
    scanf("%d",&n);

    //calling function.
    result = is_prime(n);//actual parameter.

    if(result == 1)//if 'is_prime()' will return 1,
    {            // then number is prime,otherwise not
        printf(Prime Number);
    }
    else
        printf("Not an Prime Number");
}

Output2

Enter the Number:1

Not an Prime Number

Using above define function 'is_prime()':

void main()

{
    int n,result;

    printf("Enter the Number");
    scanf("%d",&n);

    //calling function.
    result = is_prime(n);//actual parameter.

    if(result == 1)//if 'is_prime()' will return 1,
    {            // then number is prime,otherwise not
        printf(Prime Number);
    }
    else
        printf("Not an Prime Number");
}

Output1

Enter the Number:7

Prime Number

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