Circle Calculator

/* Circle Calculator */

#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <windows.h>
#include <math.h>

#define PI 3.1415

void main_menu();
void clear();
void circler();
void triangle();
void rectangle();
void proceed(int instruction);
void(*f[3])() = { circler, triangle, rectangle };

int main() {

    main_menu();

    return 0;
}


void proceed(int instruction)
{
    int menu;
    printf("\n\n 0 Continue\n"
        " 1 Main menu...\n"
        " Instruction: ");
    scanf("%d", &menu);
    if (menu == 0) {
        (*f[instruction])();
    }
    else {
        main_menu();
    }

}


void rectangle()
{
    clear();
    printf("Rectangle\n");
    proceed(2);
}



void triangle()
{
    clear();
    printf("Triangle\n");
    proceed(1);
}


void circler()
{
    void calc_cicler(double r, double d, double U, double A);

    clear();
    int instruction;
    printf("\t\tCircles\n\n"
        "       *  *        0\tRadius\n"
        "    *        *     1\tDiameter\n"
        "   *          *    2\tPerimeter\n"
        "   *          *    3\tArea\n"
        "    *        *     4\tMain menu\n"
        "       *  *        \n"
        "                   Instruction: ");

    scanf("%d", &instruction);


    double radius = 0;
    double diameter = 0;
    double perimeter = 0;
    double area = 0;

    switch (instruction) {
    case 0:
        printf("\n\n\tInform the radius: ");
        scanf("%lf", &radius);
        break;
    case 1:
        printf("\n\n\tInform the diameter: ");
        scanf("%lf", &diameter);
        break;
    case 2:
        printf("\n\n\tInform the perimeter: ");
        scanf("%lf", &perimeter);
        break;
    case 3:
        printf("\n\n\tInform the area: ");
        scanf("%lf", &area);
        break;
    default:
        main_menu();
    }

    calc_cicler(radius, diameter, perimeter, area);
    proceed(0);
}

void calc_cicler(double r, double d, double U, double A) {
    clear();

    if (d != 0) {
        r = d / 2;
        printf("\n Radius:"
            "\t\tr = d : 2\n"
            "\t\tr = %.2lf : 2\n"
            "\t\tr = %.2f\n", d, r);
    }
    else if (U != 0) {
        r = U / (2 * PI);
        printf("\n Radius:"
            "\t\tr = U : (2pi)\n"
            "\t\tr = %.2lf : (2pi)\n"
            "\t\tr = %.2f\n", U, r);
    }
    else if (A != 0) {
        r = sqrt(A / PI);
        printf("\n Radius:"
            "\t\tr^2 = A : pi\n"
            "\t\tr^2 = %.2lf : pi\n"
            "\t\tr = %.2f\n", A, r);
    }

    A = r * r * PI;
    printf("\n Area:\t\tA = pi * r^2\n"
        "\t\tA = pi * %.2lf^2\n"
        "\t\tA = %.2f\n", r, A);

    U = r * PI * 2;
    printf("\n Perimeter:"
        "\tU = 2 * pi * r\n"
        "\t\tU = 2 * pi * %.2lf\n"
        "\t\tU = %.2f\n", r, U);

    d = r * 2;
    printf("\n Diameter:"
        "\td = 2 * r\n"
        "\t\td = 2 * %.2lf\n"
        "\t\td = %.2f\n", r, d);

    printf("\n\n Radius = %.2lf\n"
        " Diameter = %.2lf\n"
        " Perimeter = %.2lf\n"
        " Area = %.2lf\n", r, d, U, A);

}


void clear() {

    DWORD n;                        /* Número de caracteres escritos */
    DWORD size;                     /* número de caracteres visíveis */
    COORD coord = { 0, 0 };         /* Posição superior esquerda da tela */
    CONSOLE_SCREEN_BUFFER_INFO csbi;

    /* Obter um identificador para o console */
    HANDLE h = GetStdHandle(STD_OUTPUT_HANDLE);

    GetConsoleScreenBufferInfo(h, &csbi);

    /* Encontre o número de caracteres a serem sobrescritos */
    size = csbi.dwSize.X * csbi.dwSize.Y;

    /* Sobrescrever o buffer de tela com espaços em branco */
    FillConsoleOutputCharacter(h, TEXT(' '), size, coord, &n);
    GetConsoleScreenBufferInfo(h, &csbi);
    FillConsoleOutputAttribute(h, csbi.wAttributes, size, coord, &n);

    /* Redefine o cursor para a posição superior esquerda */
    SetConsoleCursorPosition(h, coord);

}

void main_menu() {

    clear();
    int instruction;

    printf("\tCalculator:\n\n"
        "\t0 \tCircle\n"
        "\t1 \tTriangle\n"
        "\t2 \tRectangle\n"
        "\t3 \tExit\n\n"
        "\tInstruction: ");

    scanf("%d", &instruction);

    if (instruction >= 0 && instruction < 3) {
        (*f[instruction])();
    }

}