/*
 * Your homework assignments:
 * 1. Initialize every variable!
 * 2. Test every scanf! Handle invalid input!
 * 3. Try to think of any conditions that can crash your program!
 *
 *    DON'T LET YOUR ROCKET EXPLODE.
 */

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

void main()
{
    int m,y,w,clw,cld;
    float a = 0, b = 0;
    char ch = 0;

    printf("Please enter:\nL to solve a linear equation\nD to calculate the number of days in month\nW to calculate the number of weeks and days\n");
    fflush(stdin);
    scanf("%c",&ch);

    if (ch=='L')
    {
        printf("Please enter the equation ax+b=0 arguments: a and b\n");

        fflush(stdin);
        if (scanf("%f %f", &a, &b) == 2)
        {
            if (a==0 && b==0)
                printf("There are infinity solutions for the equation\n");

            else if (a!=0)
                printf("There is a single solution for the equation: %f\n", -b/a);

            else if (a==0 && b!=0)
                printf("There is no solution for the equation\n");
        }
        else
            printf("Invalid input!\n");
    }

    else if (ch=='D')
    {
        printf("Please enter the month and the year\n");
        scanf("%d %d", &m,&y);

        if (m==1 || m==3 ||m==5 || m==7 || m==8 || m==10 || m==12)
            printf("The number of days in month 31\n");

        else if (m==4 || m==6 || m==9 || m==11)
                printf("The number of days in month 30\n");

        else if (m==2 && !(y%4) && (y%400))
            printf("The number of days in month 29\n");

        else
        {
            if (m==2)
                printf("The number of days in month 28\n");
        }
    }

    else if (ch=='W')
    {
        printf("Please enter the number of days:\n");
        scanf("%d", &w);
        clw=w/7;
        cld=w%7;
        printf("The number of weeks is: %d weeks and %d days\n", clw,cld);
    }

    else
        printf("Invalid character!\n");
}