In this example, you will take a number from the user and find the nth prime number in the C++ program.
The number which will divide by 1 or itself is called a prime number except 1, for example, 2, 3, 5, 7, etc are prime numbers.
input: 5 output: 11
For example, if the user enters 5 then the 5th prime number is 11.
#include<iostream>
using namespace std;
int main()
{
int num,PrimeCount=0,i,flag,prime=1;
cout << "enter the number:";
cin >> num;
while(num!=PrimeCount)
{
flag=0;
prime++;
for(i=2;i<=(prime/2);i++)
{
if(prime%i==0)
flag=1;
}
if(flag==0)
{
PrimeCount++;
}
}
cout << num << "th prime number is:"<<prime;
return 0;
}
enter the number:6 6th prime number is:13
Take a number from the user and stored it in variable num.
Iterate loop until PrimeCount is equal to num.
Inside the outer loop, iterate the inner loop from 2 to prime/2. (inner loop find the prime number)
inside the inner loop, check if the remainder is zero i.e prime%i==0, then set the flag=1. (flag=1 means the number is not prime).
In the outer loop, use the if-statement to check flag value is zero i.e flag==0, if the flag value is zero then the number is prime, inside the if-statement increment value of PrimeCount.
#include<iostream>
using namespace std;
int FindNthPrime(int num);
int main() {
int num, prime = 1;
cout << "enter the number:";
cin >> num;
prime = FindNthPrime(num);
cout << num << "th prime number is:" << prime;
return 0;
}
int FindNthPrime(int num) {
int PrimeCount = 0, i, flag, prime = 1;
while (num != PrimeCount)
{
flag = 0;
prime++;
for (i = 2; i <= (prime / 2); i++)
{
if (prime % i == 0)
flag = 1;
}
if (flag == 0) {
PrimeCount++;
}
}
return prime;
}
enter the number:5 5th prime number is:11