# The speed of sound depends on the material the sound is passing through.

### CHALLENGE:

4.18:The Speed of Sound
The speed of sound depends on the material the sound is passing through.
Below is the approximate speed of sound (in feet per second) for air, water and steel:
air: 1,100 feet per second
water: 4,900 feet per second
steel: 16,400 feet per second

Write a program that displays a menu allowing the user to select air, water, or steel.
After the user has made a selection, he or she should be asked to enter the distance a sound wave will travel in the selected medium.
The program will then display the amount of time it will take.

Select a medium:
1. Air
2. Water
3. Steel

### SOLUTION:

```
#include <iostream>
#include <iomanip>
using namespace std;

int main(){
const double AIR = 1100;
const double WATER = 4900;
const double STEEL = 16400;

const int AIR_CHOICE = 1;
const int WATER_CHOICE = 2;
const int STEEL_CHOICE = 3;

int choice;
double distance;
double speed;
double time;

cout << "Select a medium:\n" << "1. Air\n" << "2. Water\n" << "3. Steel\n\n" << "Enter your choice: ";
cin >> choice;

cout << fixed << showpoint << setprecision(4);

switch(choice){
case AIR_CHOICE:
speed = AIR;
cout << "Enter the distance: ";
cin >> distance;

if (distance > 0){
time = distance / speed;
cout << "\nA sound wave takes " << time << " seconds to travel " << distance << " feet through air.\n";
} else {
cout << "\nDistance must be greater than zero.\n";
}
break;

case WATER_CHOICE:
speed = WATER;
cout << "Enter the distance: ";
cin >> distance;

if (distance > 0){
time = distance / speed;
cout << "\nA sound wave takes " << time << " seconds to travel " << distance << " feet through water.\n";
} else {
cout << "\nDistance must be greater than zero.\n";
}
break;

case STEEL_CHOICE:
speed = STEEL;
cout << "Enter the distance: ";
cin >> distance;

if (distance > 0){
time = distance / speed;
cout << "\nA sound wave takes " << time << " seconds to travel " << distance << " feet through steel.\n";
} else {
cout << "\nDistance must be greater than zero.\n";
}
break;

default:
cout << "\nThe valid choices are 1 through 3. Run the\n" << "program again and select one of those.\n";
}

return 0;
}

```