I have made a program on prime number but when i run the program and enter a number it says it's not a prime number.what's wrong

Question

https://code.sololearn.com/cX9lWbD775yH/?ref=app

Answer 1

Mirielle🐶 Actually 1 is a prime number by definition, so only 0 should be excluded.

Disha Dey The best solution is to create a function which returns whether or not an integer is a prime number:

#include<iostream>

bool is_prime(int n) {
if (n == 0) {
return false;
} else if (n < 0)
{
n *= -1;
}

for (int i = 2; i < (n/2)+1; i++) {
if (n % i == 0) {
return false;
}
}

return true;
}

int main(int argc, const char *argv[]) {

std::cout << is_prime(31) << std::endl;

return 0;
}

https://code.sololearn.com/cMufni2rO4mT/?ref=app
https://code.sololearn.com/c8VMWT7STHK7/?ref=app
https://code.sololearn.com/wg6lZE1tg98c/?ref=app

If you want output instead of boolean return value, just add another function:

void print_prime(const int n) {
std::cout << n << " is ";
if (!is_prime(n)) {
std::cout << "not ";
}
std::cout << "a prime number!" << std::endl;
}

and call this from your int main() function instead.

Answer 2

Try this code for beginners
please upvote if it helped *_*

#include<stdio.h>
#include<conio.h>
#include<iostream.h>
void main()
{
int n, f, p=0;
cout<<"enter any no to check if it is prime";
cin>>n;
for(f=1;f<=n;f++)
{
if (n%f==0)
p++;
}
cout<<\n<<p;
if(p==2)
cout<<"it is a prime number";
else
cout<<"it is not a prime number";
getch();
}

Answer 3

Disha Dey It's working fine with logic but errors in class declarations and naming. ...
1) Remove 3rd line int main() put class prime{
2)void display () missing {
3) comment clrscr()
4) make main() return type int, not void

Answer 4

#include <iostream>

using namespace std;

class prime {
public: int num, i, j = 0;
public:
void display(){
cout << "Enter number: ";
cin >> num;
for (i = 2; i < num; i++)
{

if ((num % i) == 0)
{
j++;
}
}

if (j == 0 && num !=1)
cout <<" is a prime number";
else
cout <<" is not a prime number";
}
};
int main()
{
//clrscr();
prime p;
p.display();

}

Answer 5

But the answer is coming it is not a prime number even if i write a prime number or not

Answer 6

Disha Dey run this exactly same..

#include <iostream>
using namespace std;
class prime{
int num, i, j = 0;
public:
void display(){
cout << "Enter number: ";
cin >> num;
for (i = 1; i <= num; i++)
if ((num % i) == 0)
j++;
if (j == 2)
cout <<num<<" is a prime number";
else
cout <<num<<" is not a prime number";
}};
int main()
{
// clrscr();
prime p;
p.display();
return 0;
}

Answer 7

In 4th line when i write j=0 a error comes " cannot initialize a class member here"

Answer 8

Variable j you declared as private, you can use it in any where in that class but not outside.
And in your program, am not getting any warnings, as I pasted same code in above post. Run it once...
In case, if you assign outside class, then error comes...

Answer 9

#include <iostream>
using namespace std;

int main() {
int num, i, j;
public:
void display()
cout << "Enter number: ";
cin >> num;
for (i = 1; i <= num; i++)
{
if ((num % i) == 0)
{
j++;
}
}
if (j == 0)
cout <<" is a prime number";
else
cout <<" is not a prime number";
}
};
void main()
{
clrscr();
prime p;
p.display();
return 0;
}
If i write like this and run the program and i enter a number for example 17 it says it's not a prime number

Answer 10

You are checking as j==0 instead of j==2.

Answer 11

Then what should i write.I'm confused little bit.

Answer 12

Is this above program, running on your compiler correctly ?
Prime 17
1%17=0 =>j=1
17%17=0 =>j=2. //for any prime number only 2 factors exists. So condition must be
Then
if(j==2)
cout<<"prime"; //else no... Your condition in 1st posted code is correct. Keep the same..

Answer 13

But answer is not coming

Answer 14

Line 12 to 20 copy and paste in your compiler. It will be same any compiler..
https://code.sololearn.com/cbDpNuG6v8Vf/?ref=app

Answer 15

write j=0 a error comes " cannot initialize a class member here" and if i remove and run the program then i am not getting prime number

Answer 16

I'm not able to understand how you getting error? While the Program I posted above giving me correct output without errors..
What are the changes with above one comparing with your which you are running..?
Edit:
Are your writing in if like j==2 or j=2?

Answer 17

Please write more readable

Answer 18

void main()
{
int a;
clrscr();
printf(“ Enter a number “);
scanf(“%d”,&a);
if(a==1)
printf(“ %d is not prime “, a);
else if(a==2 || a==3 || a==5 || a==7)
printf(“ %d is prime “, a);
else
{
if(a%2==0 || a%3==0 || a%5==0 || a%7==0)
printf(“ %d is composite “, a);
else
printf(“ %d is prime “, a);
}
getch();
}

Answer 19

It is a c program

Answer 20

Disha Dey you have to see logic

IN C printf();

IN CPP cout<<;

IN JAVA System.out.println();

IN PYTHON print() etc