In this article, we will learn how to write a C program to print prime numbers from 1 to 100. We will also see a program to display prime numbers from 1 to n where value of n is entered by user.
Program to print Prime Numbers from 1 to 100
In this program, we have a user defined function checkPrimeNum(), this function checks whether the number is prime or not.
We are running a loop from 1 to 100, inside this loop we are calling checkPrimeNum() to check every number between 1 and 100. If this function returns 1 we are displaying the number else we are ignoring it, thus printing only prime numbers from 1 to 100.
#include <stdio.h>
int checkPrimeNum(int num)
{
// Any number less than 2 is not a prime number
if(num < 2){
return 0;
}
//if greater than 2 then check for prime number
else{
int temp = num/2;
for(int i = 2; i <=temp; i++)
{
if(num % i == 0)
{
//return 0 if number is not prime
return 0;
}
}
}
// return 1 if number is prime
return 1;
}
int main()
{
// change this number as per the requirement. Here, we are printing
// the prime numbers from 1 to 100 so the n is 100. If you
// want to display first 50 prime numbers then change it to 50
int n = 100;
printf("Prime numbers from 1 to %d: ", n);
for(int i=1; i <= n; i++){
if(checkPrimeNum(i))
printf("%d ",i);
}
return 0;
}
Output:
Program to print Prime Numbers from 1 to N
The logic used in this program is similar to the first program. Here, we are displaying prime numbers from 1 to n, the value of n is entered by user. This value is captured using scanf() and a loop runs from 1 to n to print first n prime numbers.
#include <stdio.h>
int checkPrimeNum(int num)
{
// Any number less than 2 is not a prime number
if(num < 2){
return 0;
}
//if greater than 2 then check for prime number
else{
int temp = num/2;
for(int i = 2; i <=temp; i++)
{
if(num % i == 0)
{
//return 0 if number is not prime
return 0;
}
}
}
// return 1 if number is prime
return 1;
}
int main()
{
int n;
//taking the value of n from user
printf("Enter the value of n: ");
scanf("%d", &n);
printf("First %d prime numbers: ", n);
for(int i=1; i <= n; i++){
if(checkPrimeNum(i))
printf("%d ",i);
}
return 0;
}
Output:
Enter the value of n: 10 First 10 prime numbers: 2 3 5 7
Practice same program in Java.