HW8.1

#include <stdio.h>
#include <conio.h>
#include <math.h>

#define M_PI 3.14159265358979323846
#define EPS 1e-14

int main () {
    double res, input, x, prev_res, init;
    char choice;
    int isInput = 0, sign, i, isOut = 0, tmp;
    do {
        printf("---------------- SCIENTIFIC CALCULATOR ------------------\n");
        printf("N. Enter x\n");
        printf("Compute:\n");
        printf("\tS. Sin of x (sin(x))\n");
        printf("\tC. Square root of x (sqrt(x))\n");
        printf("\tE. Natural exponential (e^x)\n");
        printf("T. Exit\n");
        printf("\n---------------------------------------------------------\n");
        printf("\n>>>> Enter your choice (N/S/C/E/T): ");
        scanf("%c", &choice);
        while (getchar() != '\n');
        printf("---------------------------------------------------------\n");
        if (choice >= 'a' && choice <= 'z') {
            choice -= 32;
        }
        switch (choice) {
            case 'N':
                isInput = 0;
                do {
                    printf("> Enter positive number x: ");
                    tmp = scanf("%lf", &x);
                    while (getchar() != '\n');
                    if (tmp != 1) {
                        printf("!!! Please enter a number x !!!\n");
                    } else if (x < 0) {
                        printf("!!! Please enter a positive number !!!\n");
                    } else {
                        isInput = 1;
                    }
                } while (!isInput);
                putchar('\n');
                break;
            case 'S':
            case 'C':
            case 'E':
                if (!isInput) {
                    printf("!!! Please enter x first !!!\n");
                } else switch (choice) {
                    case 'S':
                        sign = -1;
                        i = 1;
                        input = x;
                        while (input > 2*M_PI) {
                            input -= 2*M_PI;
                        }
                        init = input;
                        res = input;
                        do {
                            input *= (init / (i+1)) * (init / (i+2));
                            i += 2;
                            res += sign * input;
                            sign = - sign;
                        } while (fabs(input) > EPS);
                        printf("> sin(%.4lf) = %.15lf\n\n", x, res);
                        break;
                    case 'C':
                        res = x;
                        do {
                            prev_res = res;
                            res = (res + x / res) / 2;
                        } while (fabs(prev_res - res) > EPS);
                        printf("> sqrt(%.4lf) = %.15lf\n\n", x, res);
                        break;
                    case 'E':
                        res = 1;
                        i = 1;
                        input = 1;
                        do {
                            prev_res = res;
                            input *= x / i;
                            ++i;
                            res += input;
                        } while (fabs(input) > EPS);
                        printf("> e^%.4lf = %.15lf\n\n", x, res);
                        break;
                    break;
                    }
                break;
            case 'T':
                isOut = 1;
                printf("\n!!! Good bye & See you later !!!\n");
                break;
            default:
                printf("!!! Your choice you entered is invalid. Please try again !!!\n");
                break;
        }
    } while (!isOut);
    getch();
    return 0;
}