sk1

#include <string.h>
#include <stdio.h>
#include <time.h>

double f(double x) {
    return x * x * x * x + 2 * x * x * x - x - 1;
}

double solve(double a, double b, double e) {
    double c;
    while (b - a > e) {
        c = (a + b) / 2;
        if (f(b) * f(c) < 0)
            a = c;
        else
            b = c;
    }
    return (a + b) / 2;
}

int main(int argc, char *argv[]) {
    double res, a, b, eps = 0.000001;
    if (argc == 1) {
        printf("Please enter one of the following keys: -f, -c\n");
        return 0;
    }
    if (strcmp(argv[1], "-c") == 0) {
        scanf("%lf %lf", &a, &b);
        clock_t begin = clock();
        res = solve(a, b, eps);
        clock_t end = clock();
        printf("%lf\n", res);
        double time_spent = (double) (end - begin) / CLOCKS_PER_SEC;
        printf("Program execution time: %lf\n", time_spent);
    } else if (strcmp(argv[1], "-f") == 0) {
        if (argc != 4) {
            printf("Incorrect input\n");
            return 0;
        }
        FILE *input, *output;
        input = fopen(argv[2], "r");
        output = fopen(argv[3], "w");
        if ((input == NULL) || (output == NULL)) {
            printf("Incorrect input\n");
            return 0;
        }
        fscanf(input, "%lf %lf", &a, &b);
        clock_t begin = clock();
        res = solve(a, b, eps);
        clock_t end = clock();
        fprintf(output, "%lf\n", res);
        double time_spent = (double) (end - begin) / CLOCKS_PER_SEC;
        printf("Program execution time: %lf\n", time_spent);
        fclose(input);
        fclose(output);
    } else {
        printf("Please enter one of the following keys: -f, -c\n");
    }
    return 0;
}