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

int main()
{

    char selection;

    //declaration for programs:
    //prog1:
    char printing[100];
    //prog2:
    float p1_a,p1_b,area;
    //prog3:
    float value1,value2,meanvalue;
    //prog4:
    float p4_a,p4_b,identity1,identity2;
    //prog5:
    float p5_a,p5_b,p5_c,angle;
    //prog6:
    float x,value;


    printf("This is full exercise 3. Choose which example you want to go to.\nTo terminate program type; q\n");
    printf("-------------------------------\n");
    printf("a) 1.   Implement a program which prints on the screen the text inputted by a user with a keyboard.\n");
    printf("b) 1.   Implement a program which prints on the screen the text inputted by a user with a keyboard.\n");
    printf("c) 3.   Write a program which calculates an arithmetic mean of two any values.\n");
    printf("d) 4.   Write a program which checks the following identity:  (a+b)(a-b) = a2-b2\n");
    printf("e) 5.   Having two legs of a rectangular triangle calculate its hypotenuse and angles in degrees\n");
    printf("f) 6.   Write a program which calculates values of the following function: f(x)=2x^2+3x-1 for xe<-5,5> & f(x)=(x+5)^2-10 for x<-5 v x>5\n");
    printf("-------------------------------\n");
    do
    {
        printf("Choose your destiny: ");
        selection=getchar();
        if((selection=='q')||(selection=='Q'))
        {
            printf("Terminating program.\n");
            return 0;
        }
        switch(selection)
        {
        case 'a':
            printf("Executing program %c.\n", selection);
            goto program1;
            break;
        case 'b':
            goto program2;
            break;
        case 'c':
            goto program3;
            break;
        case 'd':
            goto program4;
            break;
        case 'e':
            goto program5;
        case 'f':
            goto program6;
            break;
        default:
            printf("%c is a wrong selection. Try again\n", selection);

        }

    }
    while ((selection!='q') || (selection!='Q'));
    return 0;

/////////programs:

program1:
    system("cls");
    printf("Exercise: 1.    Implement a program which prints on the screen the text inputted by a user with a keyboard.\n");
    printf("Write something then:\n");
    fflush(stdin);
    gets(printing);
    printf("You have written: %s", printing);

program2:
    system("cls");
    printf("Exercise: 2.    Write a program which calculates the area of  one figure. Parameters of the figure are inputted by the user with a keyboard.\n");
    printf("\nEnter value of first side of a figure: ");
    scanf("%f", &p1_a);
    printf("\nEnter value of second side of a figure: ");
    scanf("%f",&p1_b);
    area=p1_a*p1_b;
    printf("\nTotal area of your figure with sides: %fx%f is: %f",p1_a,p1_b,area);
    return 0;

program3:
    system("cls");
    printf("Exercise: 3.    Write a program which calculates an arithmetic mean of two any values.\n");
    printf("\nEnter value of x1; ");
    scanf("%f",&value1);
    printf("\nEnter value of x2; ");
    scanf("%f",&value2);
    meanvalue=(value1+value2)/2;
    printf("\nMean value of %f and %f is; %f",value1,value2,meanvalue);
    return 0;

program4:
    system("cls");
    printf("Exercise: 4.    Write a program which checks the following identity:  (a+b)(a-b) = a2-b2\n");
    printf("\nEnter any value of a; ");
    scanf("%f",&p4_a);
    printf("\nEnter any value of b; ");
    scanf("%f",&p4_b);
    identity1=(p4_a+p4_b)*(p4_a-p4_b);
    identity2=p4_a*p4_a-p4_b*p4_b;
    if(identity1==identity2)
    {
        printf("\nFor left side; %f and right side; %f the identity is true", identity1,identity2);
    }
    else
    {
        printf("\nFor left side; %f and right side; %f the identity is false.\n",identity1,identity2);
    }
    return 0;

program5:
    system("cls");
    printf("Exercise: 5.    Having two legs of a rectangular triangle calculate its hypotenuse and angles in degrees\n");
    printf("\nEnter value of the first leg\n");
    scanf("%f", &p5_a);
    printf("\nEnter value of the second leg\n");
    scanf("%f", &p5_b);
    p5_c=sqrt(p5_a*p5_a+p5_b*p5_b);
    angle=acos(p5_b/p5_c)*180;
    printf("Value of a hypotenuse is %.2f and angle between legs is %.2f", p5_c,angle);
    return 0;

program6:
    system("cls");
    printf("Exercise: 6.    Write a program which calculates values of the following function: f(x)=2x^2+3x-1 for xe<-5,5> & f(x)=(x+5)^2-10 for x<-5 v x>5\n");
    printf("\nEnter value for your x: ");
    scanf("%f",&x);
    if((x>='-5')||(x<='5'))
    {
        value=2*x*x+3*x*x-1;
        printf("For x; %f value of your function is: %f\n",x,value);
    }
    if((x<'-5')&&(x>5))
    {
        value=(x+5)*(x+5)-10;
        printf("For x; %f value of your function is: %f\n",x,value);
    }
    return 0;


    system("PAUSE");
    return 0;
}