qqqqq

#include <iostream>
#include <iomanip>
#include <cmath>
using namespace std;
int main (){
    int a=2, b=4, n=20;
    double x=5.5, d=a, c[n], h, p=1, l1, l2=0, f[n];
    h=0.1;
    cin >> x;
    cout << "x" << "\t" << "y(x)"<<endl;
    for(int i=0; i<=n; i++){
        c[i]=d;
        f[i]=5*log10(d);
        d+=h;
        cout << fixed << setprecision(1) << c[i] << "\t" << fixed << setprecision(5) << f[i] << endl;
    }
    for(int j=0; j<=n; j++){
        for (int k=0; k<=n; k++){
            if (k!=j){
                p*=(x-c[k])/(c[j]-c[k]);
            }
        }
        l2+=f[j]*p;
        p=1;
    }
    l1=5*log10(x);
    if (x=2) {
            cout << "y(" << x << ")" <<endl;
            cout << fixed << setprecision(18) << l1 << "- Исходная функция" << endl << l1 << " -Лагранж ";
             }
    else
        {
            cout << "y(" << x << ")" <<endl;
            cout << fixed << setprecision(18) << l1 << "- Исходная функция" << endl << l2 << " -Лагранж ";
        }
    return 0;
}