Week4: Looping Statements in C (for, while, do-while)

Q1. Check Prime Number

Question:
Write a program to check if a number is prime or not using a for loop.

Program:

#include <stdio.h>

int main() {
    int num, i, isPrime = 1;
    printf("Enter a number: ");
    scanf("%d", &num);

    if (num <= 1) {
        isPrime = 0;
    } else {
        for (i = 2; i * i <= num; i++) {
            if (num % i == 0) {
                isPrime = 0;
                break;
            }
        }
    }

    if (isPrime) {
        printf("%d is prime.\n", num);
    } else {
        printf("%d is not prime.\n", num);
    }

    return 0;
}
````

---

## Q2. Magic Number Using `do-while`

**Question:**
Write a program to check if a number is a magic number using a `do-while` loop.

**Hint:**

* Find the sum of the digits of the given number.
* If the product of the sum and the reverse of the sum equals the given number, then it is a magic number.

Example:

Number: 1729 Sum of digits: 1+7+2+9 = 19 Reverse of sum: 91 Product: 19 * 91 = 1729 → Magic number

**Program:**

```c
#include <stdio.h>

int reverse(int num) {
    int rev = 0;
    while (num != 0) {
        rev = rev * 10 + num % 10;
        num /= 10;
    }
    return rev;
}

int main() {
    int num, sum = 0;
    printf("Enter a number: ");
    scanf("%d", &num);

    int temp = num;
    do {
        sum += temp % 10;
        temp = temp / 10;
    } while (temp != 0);

    int revSum = reverse(sum);
    if (num == sum * revSum) {
        printf("%d is a magic number.\n", num);
    } else {
        printf("%d is not a magic number.\n", num);
    }

    return 0;
}

---

Q3. Factorial of Numbers from 1 to n

Question: Write a program to print factorials of all numbers from 1 to n using nested loops.

Example:

If user input is 5, output should be:
Factorial of 1 = 1
Factorial of 2 = 2
Factorial of 3 = 6
Factorial of 4 = 24
Factorial of 5 = 120

Program:

#include <stdio.h>

int main() {
    int n, i, j, factorial;

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

    for (i = 1; i <= n; i++) {
        factorial = 1;
        for (j = 1; j <= i; j++) {
            factorial *= j;
        }
        printf("Factorial of %d = %d\n", i, factorial);
    }

    return 0;
}

---

Q4. Fibonacci Series Using Loop

Question: Write a program to print the Fibonacci series using a loop.

Program:

#include <stdio.h>

int main() {
    int n, i, first = 0, second = 1, next;

    printf("Enter the number of terms: ");
    scanf("%d", &n);

    printf("Fibonacci Series: ");
    for (i = 0; i < n; i++) {
        if (i <= 1) {
            next = i;
        } else {
            next = first + second;
            first = second;
            second = next;
        }
        printf("%d ", next);
    }

    printf("\n");
    return 0;
}

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