CECS282 - Homework 2: - Solved

Overview
In this lab, you will make a simple text-based game about hitting randomly placed targets by shooting bombs from a cannon. The player will repeatedly enter an angle to re the cannon at and an amount of gunpowder to use; your game will respond with how far away from the target the player’s shot landed. You will repeatedly ask for an angle and gunpowder amount until the player’s shot lands within 1 meter of the target. If a shot is too long or short, the player is told how far away the shot was and tries again.

Game Rules
1.    The game begins by asking the user to enter a positive integer seed value for the game’s randomnumber generator. Use this number when creating a default_random_engine variable instead of random_device. The seed value must be positive before continuing. Use the mt19937 generator instead of default_random_engin. Example:

int seed;

// input and validate seed, then: mt19937 engine{ seed };

2.    The target is placed at a random distance from 1 to 1000 meters using the random number generator;the distance can contain decimals. We have only seen how to generate integers in C++, so you will need to look up how to use uniform_real_distribution<double> to generate a decimal number in a certain range. Tell the user how far away the target is. Print all decimal values using 2 decimal places.

3.    If you generate the distance correctly, your output should match mine in the Sample Output belowwhen using the same seed value.

4.    Ask the player to choose an angle between 0 and 90 degrees, which you must validate. Then input an amount of gunpowder in kilograms, which must be positive. Both values can be decimal numbers. Each kg of gunpowder will produce 30 m/s of velocity.

5.    The shot’s total distance is calculated, and if the shot is within 1.0 m of the target, the shot is scoreda hit and the player wins. Otherwise the player is told how far short or long of the target the shot landed, and must try again.

6.    The game ends when the player gets a hit.

Physics
Given an initial velocity v and angle of elevation A, the bomb’s initial speed can be broken into vertical and horizontal components (vy and vx respectively) by the equations vy = v ·sin(A) and vx = v ·cos(A). There are two ways to nd the bomb’s nal position:

1.    Using a formula for nding the position of a projectile given its initial velocity and angle of elevation, determine the time it takes for the bomb to return to ground level. (Hint: consider the height or y-coordinate of the bomb the instant it touches the ground.)

2.    Using the vertical component of the initial velocity (vy), determine how long it takes for the e ect of gravity to reduce that velocity to zero. This is the time it takes for the bomb to reach the apex of its arc. Double that amount for the time it takes to return to the ground.

Once you have the time it takes for the bomb to hit the ground, you can nd how far it travels in the horizontal direction using the horizontal component of the initial velocity (vx).

Functions
I will strongly recommend but not require that you organize your solution into functions. To best practice this week’s lessons, you should have a C++ project that

•    uses a header            le to declare functions useful in breaking down your game into smaller parts.

•    uses a source             le with the same name to de ne/implement those functions.

•    uses a main.cpp         le that #includes your header and writes the driver of the application by calling the functions you de ned in the other source  le.

Try breaking the problem description into discrete abstract tasks:

•    maybe a function to get and validate the user’s chosen attack angle?

•    maybe a function to get and validate the user’s amount of gunpowder?

•    maybe a function to calculate how far a projectile would travel when red at a given angle and with given velocity?

•    maybe a function to determine if a particular distance is a             hit           when compared to a given target distance?

Notes and Hints
1.    The <cmath> library has methods for calculating sines and cosines, but they operate on radians and not degrees.

2.    Use g = 9.8m/sec2 for the vertical acceleration of the bomb, and use π = 3.141592653589793238463 if you need it.

3.    Use double for any decimal numbers instead of float.

4.    Having trouble deciding where to start? Try this approach.

(a)     Build a program that sets the target’s distance to 500 every time. Ask the user how far the shellshould go, and tell them whether the shot was short, long, or a hit. (Goal: get the hit detection working.)

(b)     Add prompts for the user to enter the angle of elevation and gunpowder amount, without anyerror checking. Compute the distance from those inputs. (Goal: get your formulas correct and applied to the game.)

(c)      Repeat the game until the user gets a hit. (Goal: general game             ow.) (d) Add error checking for angle and gunpowder.

(e) Add a prompt at the start for the random number generator seed, including error checking. Use this value to select a random starting distance for the target. This should complete your project.

Sample Output
User input is in italics.

Please enter a positive integer seed value:

0

Please enter a positive integer seed value:

100

The target is 671.48m away.

Please enter an angle between 0 and 90 degrees:

91

Please enter an angle between 0 and 90 degrees:

45

Please enter an amount of gunpowder in kilograms:

2

You were 304.51m short.

Please enter an angle between 0 and 90 degrees:

45

Please enter an amount of gunpowder in kilograms:

3

You were 154.20m long.

Please enter an angle between 0 and 90 degrees:

34

Please enter an amount of gunpowder in kilograms:

2.81

It’s a hit!