#include<cmath> // import cmath
#include <iostream> // import iostream
#include <math.h> // import math.h

int main() {
    using namespace std;

    struct MyStruct { // class common:
        double e;
        double b0;
        double b1;
        double m;
        double pt;
        double hdn;
        double rad0;
        double rad30;
        double rad60;
        //
        string du_material;
        double du_a;
        double du_c0;
        double du_c1;
        //
        string tha_material;
        double tha_a;
        double tha_c0;
        double tha_c1;
        //
        string tss_material;
        double tss_a;
        double tss_c0;
        double tss_c1;
    };

    MyStruct common;

    common.e = 2.7183;
    common.b0 = 0.283;
    common.b1 = 0.0656;
    common.m = -0.224;
    common.pt = 7850; // steel; 7850 kg/m3
    common.hdn = 260; // rha; 260 hb
    common.rad0 = 1;
    common.rad30 = 0.8660254037844387;
    common.rad60 = 0.5;
            //
    common.du_material = "Depleted Uranium";
    common.du_a = 0.825;
    common.du_c0 = 90;
    common.du_c1 = -0.0849;
            //
    common.tha_material = "Tungsten Heavy Alloy";
    common.tha_a = 0.994;
    common.tha_c0 = 134.5;\
    common.tha_c1 = -0.148;
            //
    common.tss_material = "Tungsten Self Sharpening";
    common.tss_a = 0.825;
    common.tss_c0 = 90;
    common.tss_c1 = -0.148;

    double x = common.du_a;
    double y = common.du_c0;
    double z = common.du_c1;

    double lw;
    double d;
    double pp;
    double v;

    int sum(double x, double y, double z, double lw, double d, double v, double pp){ <- error with red under line at curly brackets
        int i = x * (1 / (tanh(common.b0 + (common.b1 * (lw / d))))) * (common.rad0 ^ common.m) * sqrt(pp / common.pt) * common.e ^ ((-1 * ((y + (z * common.hdn)) * common.hdn) / pp) / ((v / 1000) ^ 2)) * lw)* common.rad0
        return int i
    };

    cout << "Input length of penetrator: " << endl;
    cin >> lw;
    cout << "Input diametre of penetrator: " << endl;
    cin >> d;
    cout << "Input density of penetrator material: " << endl;
    cin >> pp;
    cout << "Input initial velocity of penetrator: " << endl;
    cin >> v;

    cout << "Perforation is: " << sum << "mm at" << v << ", angle " << common.rad0 << ".\n" << endl;

    return 0;
}
우지챠 분명 맞게 쓴거 같은데 유독 함수 define에서 error가 뜨는레후