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

/* function prototypes */
void prob1(void);
void prob2(void);
void prob3(void);

/* add here additional function prototypes as needed */

main()
{
        int menu;
        printf("Enter the function number to execute (1-3):");
        scanf("%d", &menu);
        switch(menu){
         case 1:
            prob1();
            break;
         case 2:
            prob2();
            break;
         case 3:
            prob3();
            break;
         default:
            printf("prob%d() does not exist.\n", menu);
        }
        exit(0);
}
void prob1(void)
{
//printf(" Put your solution for problem 1 here:\n");

        double a_1, b_1, c_1, a_2, b_2, c_2;
        double D, D_1, D_2, x_1, x_2, y, y_1;

        printf("\nEnter a_1, b_1, c_1\n");
        scanf("%lf %lf %lf", &a_1, &b_1, &c_1);

        printf("\n\nEnter a_2, b_2, c_2\n");
        scanf("%lf %lf %lf", &a_2, &b_2, &c_2);
        printf("\n\n");
        D=a_1*b_2-b_1*a_2;
        D_1=c_1*b_2-b_1*c_2;
        D_2=a_1*c_2-c_1*a_2;
        x_1=D_1/D;
        x_2=D_2/D;
        c_1=a_1*x_1+b_1*x_2;
        c_2=a_2*x_1+b_2*x_2;
        y=sqrt(pow(x_1, 2)+pow(x_2, 2));
        y_1=log10(y);
        printf("x_1 = %f,     x_2 = %f", x_1, x_2);
        if(D=0) printf("The equations are linearly dependent\n");
        else printf("\n\nThe value of y is %f\n", y_1);
}

void prob2(void)
{
//printf(" Put your solution for problem 2 here:\n");

        int num, row, num2, *v;
        double  num1, sum;
        char text[80];
        FILE *infile, *outfile;
        infile = fopen("data.dat", "r");
        outfile = fopen("output2.dat", "w");
        if (infile == NULL)
        {
                printf(" Error Opening file!");
                exit(0);
        }


        fscanf(infile, "%d", &num);
//      printf("%d\n", num);
        v = (int *)calloc((size_t)num, sizeof(int *));
        if( v == NULL)
        {
                printf("error");
                exit (0);
        }

        printf("v[] = {");
        for(num2=0; num2<num; num2++)
        {
                fscanf(infile, "%lf", &v[num2]);
                printf("%.2f ", v[num2]);
//              sum += v[num2] * v[num2];
        }
        sum = 0;
        for(num2=0; num2<num; num2++)
        {       sum = sum + pow(v[num2], 2);
        }

        printf("}\n\n");
        printf("\nsum = %f\n", sum);
        sum = sqrt(sum);


        printf("The length of the vector v[] is %f\n", sum);
}

void prob3(void)
{
printf(" Put your solution for problem 3 here:\n");

}

        int num, row, num2, *v;

   fscanf(infile, "%lf", &v[num2]);
   printf("%.2f ", v[num2]);

   fscanf(infile, "%d", &v[num2]);
   printf("%d ", v[num2]);

    sort(v.begin(), v.end());