d

#include <iostream>
#include <sstream>
#include <fstream>
#include <ctime>
using namespace std;

stringstream str;
double q = 0.2;
double p = 0.9;
int n = 12;
int counterLB = 0;
int counterRB = 0;

void generatorLB() {

    if (rand() < p * RAND_MAX) {
        str << "(";
        counterLB++;
    }
}

void generatorRB() {

    if (rand() < q * RAND_MAX) {
        str << ")";
        counterRB++;
    }
}

void generatorOp() {
    int op = rand() % 4;
    switch (op) {
    case 0:
        str << "+";
        break;
    case 1:
        str << "-";
        break;
    case 2:
        str << "*";
        break;
    case 3:
        str << "/";
        break;
    }
}

void generate() {

    int cnt = 0;
    generatorLB();
    str << "x"; str << (cnt + 1);
    cnt++;

    while (cnt != n)
    {

        generatorOp();
        generatorLB();
        str << "x"; str << (cnt + 1);
        cnt++;
        if (counterLB != 0)
            generatorRB();

    }
    while (counterLB>counterRB)  generatorRB();

}

int main()
{
    srand(time(0));
    setlocale(LC_ALL, "Russian");
    ofstream fout("exp.txt");
    generate();
    fout << str.str();

}