incrrect result in pow and gcd function in c++

Question

this is my code for RSA cryptosystem

but I have an error with using the pow function that git an error solution

c = pow(m,e)%n;

and for gcd (greatest common divisor) I'm using #include numeric and algorithm and it does not run but I create function and will be git a solution

this is a full code

#include<iostream>
#include<cmath>
#include<math.h>
#include <algorithm>
#include<numeric>

using namespace std;

int prime(long int pr)
{
    int i;
    int j = sqrt(pr);
    for (i = 2; i <= j; i++)
    {
        if (pr % i == 0)
            return 0;
    }
    return 1;
}
    int gcd(int a, int b) {
        if (b == 0)
            return a;
        return gcd(b, a % b);
}
    
    /*int power(int a, int b) {
        float r = 1;
        while (b != 0) {
            r *= a;
            --b;
        }
        return r;
    }
    */
int main() {
    int flag,w,k;
    cout << "Welcome to RSA Project\n\n ";

    cout << "Enter First larg prime for p ";
    int p,q,phi,n,e,d;
    cin >> p;
     flag = prime(p);
    if (flag == 0)
    {
        cout << "\nINVALID INPUT\n";
        exit(0);
    }
    cout << "Enter Second larg prime for q ";
    cin >> q;
    flag = prime(q);
    if (flag == 0)
    {
        cout << "\nINVALID INPUT\n";
        exit(0);
    }
        //compute n= p*q
    n = p * q;
    // comput phi
    phi = (p - 1) * (q - 1);

    //chose e or select randomly e must be gcd(e,phi)=1
    w = 2;
    while (gcd(w, phi) != 1)
    {
        w++;
    }
    e = w;


    //chose d from random numbers 
    k = 1;
    while (((k * e) % phi) != 1)
    {
        k++;
    }
    d = k;


    cout << "\nThe public key is : " << "{ " << n << " , " << e << " }";
    cout << "\nThe private key is : " << "{ " << n << " , " << d << " }";
    cout << "\n*****\n\n p=" << p << "\nq=" << q <<"\nn="<<n<<"\nphi = " << phi << "\ne = " << e << "\nd = " << d << "\n *****";
    //Encryption
    cout << " \nEnter the message for Encrypt : ";
    int m , c;
    cin >> m;
    //c = pow(m,e)%n; ((( here  an error ))) 
    c = pow(m, e);
    c = c% n;
    cout << "\n message for encrypt : " << m;
    cout << " \nmessage after encrypt : " << c;
    //Decryption
    m = pow(c , d);
    m = c% n;
    cout << " \nmessage after decrypt : " << m;




}

output : output

it's fully tested but the error with pow function ..

if anyone can help me please ..