C Program to Check Armstrong Number of three digits

Source code:

#include <stdio.h>
int main()
{
    int number, originalNumber, remainder, result = 0;

    printf("Enter a three digit integer: ");
    scanf("%d", &number);

    originalNumber = number;

    while (originalNumber != 0)
    {
        remainder = originalNumber%10;
        result += remainder*remainder*remainder;
        originalNumber /= 10;
    }

    if(result == number)
        printf("%d is an Armstrong number.",number);
    else
        printf("%d is not an Armstrong number.",number);

    return 0;
}

Output:

Enter a three digit integer: 371
371 is an Armstrong number.

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C Program to Check Whether a Number is Positive or Negative

Source code:

#include <stdio.h>
int main()
{
    double number;

    printf("Enter a number: ");
    scanf("%lf", &number);

    if (number <= 0.0)
    {
        if (number == 0.0)
            printf("You entered 0.");
        else
            printf("You entered a negative number.");
    }
    else
        printf("You entered a positive number.");
    return 0;
}

Output 1:

Enter a number: 12.3
You entered a positive number.

Output 2:

Enter a number: 0
You entered 0.

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C Program to Display Prime Numbers Between Intervals Using Function

Source code:

#include <stdio.h>

int checkPrimeNumber(int n);
int main()
{
    int n1, n2, i, flag;

    printf("Enter two positive integers: ");
    scanf("%d %d", &n1, &n2);
    printf("Prime numbers between %d and %d are: ", n1, n2);

    for(i=n1+1; i<n2; ++i)
    {
        // i is a prime number, flag will be equal to 1
        flag = checkPrimeNumber(i);

        if(flag == 1)
            printf("%d ",i);
    }
    return 0;
}

// user-defined function to check prime number
int checkPrimeNumber(int n)
{
    int j, flag = 1;

    for(j=2; j <= n/2; ++j)
    {
        if (n%j == 0)
        {
            flag =0;
            break;
        }
    }
    return flag;
}

Output:

Enter two positive integers: 12
30
Prime numbers between 12 and 30 are: 13 17 19 23 29

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C Program to Display Prime Numbers Between Two Intervals

Source code:

#include <stdio.h>
int main()
{
    int low, high, i, flag;
    printf("Enter two numbers(intervals): ");
    scanf("%d %d", &low, &high);

    printf("Prime numbers between %d and %d are: ", low, high);

    while (low < high)
    {
        flag = 0;

        for(i = 2; i <= low/2; ++i)
        {
            if(low % i == 0)
            {
                flag = 1;
                break;
            }
        }

        if (flag == 0)
            printf("%d ", low);

        ++low;
    }

    return 0;
}

Output:

Enter two numbers(intervals): 20 
50
Prime numbers between 20 and 50 are: 23 29 31 37 41 43 47

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C Program to Check Whether a Number is Prime or Not

Source code:

#include <stdio.h>
int main()
{
    int n, i, flag = 0;

    printf("Enter a positive integer: ");
    scanf("%d",&n);

    for(i=2; i<=n/2; ++i)
    {
        // condition for nonprime number
        if(n%i==0)
        {
            flag=1;
            break;
        }
    }

    if (flag==0)
        printf("%d is a prime number.",n);
    else
        printf("%d is not a prime number.",n);
    
    return 0;
}

Output:

Enter a positive integer: 29
29 is a prime number.

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C Program to Calculate the Sum of Natural Numbers

Source code:

#include <stdio.h>
int main()
{
    int n, i, sum = 0;
    
    printf("Enter a positive integer: ");
    scanf("%d",&n);

    for(i=1; i <= n; ++i)
    {
        sum += i;   // sum = sum+i;
    }

    printf("Sum = %d",sum);

    return 0;
}

Output:

Enter a positive integer: 100
Sum = 5050

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C Program to Display Factors of a Number

Source code:

#include <stdio.h>
int main()
{
    int number, i;

    printf("Enter a positive integer: ");
    scanf("%d",&number);

    printf("Factors of %d are: ", number);
    for(i=1; i <= number; ++i)
    {
        if (number%i == 0)
        {
            printf("%d ",i);
        }
    }

    return 0;
}

Output:

Enter a positive integer: 60
Factors of 60 are: 1 2 3 4 5 6 12 15 20 30 60

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C Program to Check Whether a Number is Prime or Not

Source code:

#include <stdio.h>
int main()
{
    int n, i, flag = 0;

    printf("Enter a positive integer: ");
    scanf("%d",&n);

    for(i=2; i<=n/2; ++i)
    {
        // condition for nonprime number
        if(n%i==0)
        {
            flag=1;
            break;
        }
    }

    if (flag==0)
        printf("%d is a prime number.",n);
    else
        printf("%d is not a prime number.",n);
    
    return 0;
}

Output:

Enter a positive integer: 29
29 is a prime number.

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C Program to Check Leap Year

Source code:

#include <stdio.h>

int main()
{
    int year;

    printf("Enter a year: ");
    scanf("%d",&year);

    if(year%4 == 0)
    {
        if( year%100 == 0)
        {
            // year is divisible by 400, hence the year is a leap year
            if ( year%400 == 0)
                printf("%d is a leap year.", year);
            else
                printf("%d is not a leap year.", year);
        }
        else
            printf("%d is a leap year.", year );
    }
    else
        printf("%d is not a leap year.", year);
    
    return 0;
}

Output 1:

Enter a year: 1900
1900 is not a leap year.

Output 2:

Enter a year: 2012
2012 is a leap year.

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C Program to Calculate Area and Circumference of circle

Source Code:

#include<stdio.h>

int main() {

   int rad;
   float PI = 3.14, area, ci;

   printf("\nEnter radius of circle: ");
   scanf("%d", &rad);

   area = PI * rad * rad;
   printf("\nArea of circle : %f ", area);

   ci = 2 * PI * rad;
   printf("\nCircumference : %f ", ci);

   return (0);
}

Output:

Enter radius of a circle : 1

Area of circle : 3.14

Circumference  : 6.28

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