#include <iostream>
#include <string>
#include <cmath>

void a1()
{
    int n;
    std::cout << "Enter an integer: ";
    std::cin >> n;

    std::cout << (n >= 0 && n <= 100) << '\n';
}

void b1()
{
    int n;
    std::cout << "Enter an integer: ";
    std::cin >> n;

    if(n>0)
    {
        std::cout << n << " is greater than 0.\n";

        if(n%4==0)
        {
            std::cout << n << " is also divisible by 4.\n";
            
            if(n%3==0)
            {
                std::cout << n << " is also divisible by 3.\n";
            }
            else
            {
                std::cout<< n << " is not divisible by 3.\n";
            }
        }
        else
        {
            std::cout << n << " is not divisble by 4.\n";
        }
    }
    else
    {
        std::cout << n << " is not greater than 0.\n";
    }
}

void abcd2()
{
    std::string dna;
    std::cout << "Enter a String: ";
    std::cin >> dna;

    int g = 0;
    int a = 0;
    int c = 0;
    int t = 0;
    int G = 0;
    int A = 0;
    int C = 0;
    int T = 0;
    for(char base : dna)
    {
        switch(base)
        {
            case 'G':
                G++;
                break;
            case 'g':
                g++;
                break;
            case 'A':
                A++;
                break;
            case 'a':
                a++;
                break;
            case 'C':
                C++;
                break;
            case 'c':
                c++;
                break;
            case 'T':
                T++;
                break;
            case 't':
                t++;
                break;
            default:
                std::cout << "Error; Invalid Base: " << base << "\n";
        }
    }

    std::cout << "g: " << g << " a: " << a << " c: " << c << " t: " << t << "\n";
    std::cout << "G: " << G << " A: " << A << " C: " << C << " T: " << T << "\n";
    /*
    d)
    A switch should be used, when checking if a variable has one of many possible values.
    */
}

void ab3()
{
    const long double from = 0.0;
    const long double to = 1.0;
    long double integral_val = 0.0;
    long double x = from;
    const size_t N = 1000000;
    const long double step_width = std::abs(from - to) / static_cast<long double>(N);
    for (size_t n = 0; n < N; ++n) {
    //integral_val += 4 / (1 + x * x);
    //a: integral_val += 3*x*x;
    //b: integral_val += 2* std::sqrt(x);
    x += step_width;
    }
    integral_val /= N;
    std::cout << integral_val << '\n';
}

void c3()
{
    int sum = 0;
    for(int k=1; k<=100; k++)
    {
        sum += k;
    }
    std::cout << sum << '\n';
}

void d3()
{
    int sum = 0;
    for(int i=1; i<=10; i++)
    {
        for(int j=1; j<=10; j++)
        {
            sum += i;
        }
    }
    std::cout << sum << '\n';
}

void abc4()
{
    for(int x=0; x<10; x++)
    {
        for(int y=0; y<10; y++)
        {
            std::cout << '#';
        }
        std::cout << '\n';
    }
    std::cout << '\n';

    for(int x=0; x<10; x++)
    {
        for(int y=0; y<10; y++)
        {
            if(y==0 || y==9 || x==0 || x==9)
            {
                std::cout << '#';
            }
            else
            {
                std::cout << ' ';
            }
        }
        std::cout << '\n';
    }
    std::cout << '\n';
  
    for(int x=0; x<10; x++)
    {
        for(int y=0; y<10; y++)
        {
            if(x==y || y==0 || y==9 || x==0 || x==9)
            {
                std::cout << '#';
            }
            else
            {
                std::cout << ' ';
            }
        }
        std::cout << '\n';
    }
    std::cout << '\n';
}

int main()
{
    int selection;
    std::cout << "1: 1a\n2: 1b\n3: 2abcd\n4: 3ab\n5: 3c\n6: 3d\n7: 4abc\n";
    std::cout << "Please select an Exercise: ";
    std::cin >> selection;

    switch(selection)
    {
        case 1:
            a1();
            break;
        case 2:
            b1();
            break;
        case 3:
            abcd2();
            break;
        case 4:
            ab3();
            break;
        case 5:
            c3();
            break;
        case 6:
            d3();
            break;
        case 7:
            abc4();
            break;
        default:
            a1();
            b1();
            abcd2();
            ab3();
            c3();
            d3();
    }
    return 0;
}