- Write a C program to print all prime numbers between 1 to N using for loop.
- Wap in C to print prime numbers between 1 to 100.

#### Required Knowledge

A **Prime number** is a natural number greater than 1 that is only divisible by either 1 or itself. All numbers other than **prime numbers** are known as composite numbers. There are infinitely many prime numbers, here is the list of first few prime numbers

2 3 5 7 11 13 17 19 23 29 31 37....

**Algorithm to check whether a number is prime number or not**

*Let, N be a positive number.*

- For every number i, between 2 to N/2(2<= i <= N/2) check whether i divides N completely(check If i is a factor of N).
- if (N % i == 0), then N cannot be a Prime number.
- If none of the number between 2 to N/2 divides N completely then N is a prime number.

## C program to print all prime numbers between 1 to N using for loop

#include<stdio.h> #include<conio.h> int main(){ int N, i, j, isPrime, n; printf("To print all prime numbers between 1 to N\n"); printf("Enter the value of N\n"); scanf("%d",&N); /* For every number between 2 to N, check whether it is prime number or not */ printf("Prime numbers between %d to %d\n", 1, N); for(i = 2; i <= N; i++){ isPrime = 0; /* Check whether i is prime or not */ for(j = 2; j <= i/2; j++){ /* Check If any number between 2 to i/2 divides I completely If yes the i cannot be prime number */ if(i % j == 0){ isPrime = 1; break; } } if(isPrime==0 && N!= 1) printf("%d ",i); } getch(); return 0; }

Output

To print all prime numbers between 1 to N Enter the value of N 50 Prime numbers between 1 to 50 2 3 5 7 11 13 17 19 23 29 31 37 41 43 47

**Write a C program to find product of digits of a number using while loop.**

Wap in C to multiply the digits of a number.

Wap in C to multiply the digits of a number.

#### Required Knowledge

To **multiply digits of a number** we have to remove one digit at a time, we can use '/' division and '%' modulus operator. Number%10 will give the least significant digit of the number, we will use it to get one digit of number at a time. To remove last least significant digit from number we will divide number by 10.

**Product of digits** of 2534 = 2 x 5 x 3 x 4 = 120

**Algorithm to find product of digits of a number**

- Get least significant digit of number (number%10) and multiply it to the product variable.
- Remove least significant digit form number (number = number/10).
- Repeat above two steps, till number is not equal to zero.

## C program to find sum of all even numbers between 1 to N using for loop

#include <stdio.h> #include <conio.h> int main() { int num, temp; long productOfDigit = 1; /* * Take a number as input from user */ printf("Enter a Number\n"); scanf("%d", &num); temp = num; while(num != 0){ /* get the least significant digit(last digit) of number and multiply it to productofDigit */ productOfDigit *= num % 10; /* remove least significant digit(last digit) form number */ num = num/10; } printf("Product of digits of %d = %ld", temp, productOfDigit); getch(); return 0; }

Output

Enter a Number 2436 Product of digits of 2436 = 144

Enter a Number 2222 Product of digits of 2436 = 16

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