105c

// 2.3

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <math.h>

int thirdTask()
{
    srand(time(NULL));
    int n, zeros = 0, ones = 0, twos = 0, threes = 0, fours = 0, fives = 0, sixs = 0, sevens = 0, eights = 0, nines = 0;
    scanf("%d", &n);
    for (int i; i < n; i++)
    {
        int x, xi;
        x = rand() % 10000 + 1;
        xi = (x / 100) % 10;
        printf("%d %d \n", x, xi);
        switch(xi)
        {
            case 0:
                zeros++;
                break;
            case 1:
                ones++;
                break;
            case 2:
                twos++;
                break;
            case 3:
                threes++;
                break;
            case 4:
                fours++;
                break;
            case 5:
                fives++;
                break;
            case 6:
                sixs++;
                break;
            case 7:
                sevens++;
                break;
            case 8:
                eights++;
                break;
            case 9:
                nines++;
                break;
            default:
                break;
        }
    }
    printf("0 = %d, 1 = %d, 2 = %d, 3 = %d, 4 = %d, 5 = %d, 6 = %d, 7 = %d, 8 = %d, 9 = %d", zeros, ones, twos, threes, fours, fives, sixs, sevens, eights, nines);
    return 0;
}

// 3.2

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <math.h>

float f(float x)
{
    float y;
    y = pow(cos(x), 2);
    return y;
}

int main()
{
    FILE *file;
    file = fopen("function_values.txt", "w");
    float h, left_border, right_border;
    int i1, i2;
    printf("input step, left border, right border\n");
    scanf("%f %f %f", &h, &left_border, &right_border);
    i1 = (int)(left_border / h);
    i2 = (int)(right_border / h);
    printf("\tx_i\t\tf(x_i)\n");
    fprintf(file, "\tx_i\t\tf(x_i)\n");
    for (int i = i1; i < i2; i++)
    {
        float fxi, x = (float)i * h;
        fxi = f(x);
        printf("\t%f\t%f\n", x, fxi);
        fprintf(file, "\t%f\t%f\n", x, fxi);
    }
}

// 3.3

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <math.h>

float f(float x)
{
    float y;
    y = pow(cos(x), 2);
    return y;
}

int main()
{
    FILE *file;
    file = fopen("function_values.txt", "w");
    float h, left_border, right_border;
    float function_values[100000][3];
    int i1, i2;
    printf("input step, left border, right border\n");
    scanf("%f %f %f", &h, &left_border, &right_border);
    i1 = (int)(left_border / h);
    i2 = (int)(right_border / h);
    printf("\tx_i\t\tf(x_i)\n");
    fprintf(file, "x_i\tf(x_i)\tf'(x_i)\n");
    for (int i = i1; i < i2; i++)
    {
        float fxi, derivativei, x = (float)i * h;
        fxi = f(x);
        derivativei = (f(x - h) - f(x + h)) / (2 * h);
        function_values[i][0] = x;
        function_values[i][1] = fxi;
        function_values[i][2] = derivativei;
        printf("%f\t%f\t%f\n", x, fxi, derivativei);
        fprintf(file, "%f\t%f\t%f\n", x, fxi, derivativei);
    }
}