# C Program to Print All Prime Numbers between 1 to N

• 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.

#### 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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