C using prime number and Variance & Standard Deviation programs

Check if a given Number is Prime number

#include 

#include 

#include 

void main()

{

    int num, j, flag;

    clrscr();

    printf("Enter a number \n");

    scanf("%d", &num);

    if (num <= 1)

    {

        printf("%d is not a prime numbers \n", num);

        exit(1);

    }

    flag = 0;

    for (j = 2; j <= num / 2; j++)

    {

        if ((num % j) == 0)

        {

            flag = 1;

            break;

        }

    }

    if (flag == 0)

        printf("%d is a prime number \n", num);

     else

        printf("%d is not a prime number \n", num);

        getch();

}

Output

Enter a number

23

23 is a prime number

Enter a number

15

15 is not a prime number

Find Prime Numbers in a given Range

#include 

#include 

#include 

void main()

{

    int num1, num2, i, j, flag, temp, count = 0;

    clrscr();

    printf("Enter the value of num1 and num2 \n");

    scanf("%d %d", &num1, &num2);

    if (num2 < 2)

    {

        printf("There are no primes upto %d\n", num2);

        exit(0);

    }

    printf("Prime numbers are \n");

    temp = num1;

    if ( num1 % 2 == 0)

    {

        num1++;

    }

    for (i = num1; i <= num2; i = i + 2)

    {

        flag = 0;

        for (j = 2; j <= i / 2; j++)

        {

            if ((i % j) == 0)

            {

                flag = 1;

                break;

            }

        }

        if (flag == 0)

        {

            printf("%d\n", i);

            count++;

        }

    }

    printf("Number of primes between %d & %d = %d\n", temp, num2, count); 

getch();

}

Output

Enter the value of num1 and num2

70 85

Prime numbers are

71

73

79

83

Number of primes between 70 and 85 = 4

Calculate the Mean, Variance & Standard Deviation

#include 

#include 

#include 

#define maxsize 10

void main()

{

    float x[maxsize];

    int  i, n;

    float average, variance, std_deviation, sum = 0, sum1 = 0;

    clrscr();

    printf("Enter the value of N \n");

    scanf("%d", &n);

    printf("Enter %d real numbers \n", n);

    for (i = 0; i < n; i++)

    {

        scanf("%f", &x[i]);

    }

    for (i = 0; i < n; i++)

    {

        sum = sum + x[i];

    }

    average = sum / (float)n;

    for (i = 0; i < n; i++)

    {

        sum1 = sum1 + pow((x[i] - average), 2);

    }

    variance = sum1 / (float)n;

    std_deviation = sqrt(variance);

    printf("Average of all elements = %.2f\n", average);

    printf("variance of all elements = %.2f\n", variance);

    printf("Standard deviation = %.2f\n", std_deviation);

    getch();

}

Output

Enter the value of N

5

Enter 5 real numbers

34

88

32

12

10

Average of all elements = 35.20

variance of all elements = 794.56

Standard deviation = 28.19