Why is my program not working? Why is the error telling me to put ';' before ')'?

Question

#include <iostream>
using namespace std;

int main()
{
    int n=0, i=2
    ;bool isPrime=true
    
    ;cout<<"Enter the integer:";
    cin>>n;
    
    if (n==0 || n==1) {
        isPrime=false;
    }
    else {
        for (i=2, i<=n/2, ++i) {
            if (n%i==0) {
                isPrime=false;
                break;
            }
        }
    }
    if (isPrime) {
        ;cout<<"Your integer is a prime number."<<n<<endl;
    }
    else {
        ;cout<<"Your integer is not a prime number"<<n<<endl;
    }
    return 0;
} // end of main.

Answer 1

changes in lines number 15, 23, 26

syntax wrong in for (line 15)

extra ';'  (line 23, 26)

this code works:- https://onlinegdb.com/dpTuHD48v

Answer 2

The syntax of the for directive correctly:

for ([initialization]; [condition]; [increment])
{
    [body]
}

Notice that you need semicolons (;) not commas (,) to separate the initialization, condition and increment parts.

Notes

1. Semicolons typically are placed at the end of the line to terminate the command. While the compiler does not care about white spaces, you really confuse other human beings if the semicolons are not placed right after the command, but at the beginning of the next line.
2. Your program does not work for negative numbers. (It accept negative numbers and says all of them are primes.)

Answer 3

You have used the wrong syntax in the 'for' loop. it should be semicolon(;) instead of the comma",". Replace all commas the issue will be resolved.

Answer 4

I adjusted your code, it should work find now:

#include <iostream>
using namespace std;

int main()
{
    int n=0, i=2;
    bool isPrime=true; // Semicolons don't go before statements, but after
    
    cout<<"Enter the integer:";
    cin>>n;
    
    if (n==0 || n==1) {
        isPrime=false;
    }
    else {
        for (i=2; i<=n/2; ++i) { // Use ; instead of ,
            if (n%i==0) {
                isPrime=false;
                break;
            }
        }
    }
    if (isPrime) {
        cout<<"Your integer is a prime number."<<n<<endl;
    }
    else {
        cout<<"Your integer is not a prime number"<<n<<endl;
    }
    return 0;
} // end of main.

:)

Answer 5

https://www.programiz.com/cpp-programming/examples/prime-number

#include <iostream>
using namespace std;

int main() {

  int i, n;
  bool is_prime = true;

  cout << "Enter a positive integer: ";
  cin >> n;

  // 0 and 1 are not prime numbers
  if (n == 0 || n == 1) {
    is_prime = false;
  }

  // loop to check if n is prime
  for (i = 2; i <= n/2; ++i) {
    if (n % i == 0) {
      is_prime = false;
      break;
    }
  }

  if (is_prime)
    cout << n << " is a prime number";
  else
    cout << n << " is not a prime number";

  return 0;
}

Answer 6

#include <iostream>
using namespace std;

int main()
{
    int number;
    cout << "Enter a number ";
    cin >> number;
    int factors = 0;
    int x = number;
    do {
        if (number % x == 0) {
            factors += 1;
            --x;
        }
        else {
            --x;
        }
    }
    while (x != 0);
    if (factors == 2) {
        cout << number << " is a prime number";    
    }
    else {
        cout << number << " is not a prime number";
    }
}