An Example

We will be covering all of this later, but I would like to work through an example.

I need to borrow some money from my mom. She would like to set up a regular loan. As part of this she would like a program that calculates the interest due. Can you help write this program?

What are the problem solving steps we discussed?

Understand the problem
Develop a solution
Imiplement the solution
Use/Maintenance

Do we understand the problem?

What questions might we need answered?
- What type of loan? Simple Interest, Compunt Interest, installment payment ...
- Will it be for a fixed time, will payments be fixed?
- What will the interest rate be?
- Do we give the interest or the final payment?

Let's assume the following conditions:

A simple interest loan.
Interest rate given as a yearly amount.
Time given in years
Principal given in dollars.

Can we work through an example?

I need the simple interest formula, i = prt
A loan of $100 for 1 year at 5% interest would require a payment of $100 principal and $5 interest.
Work through it.

Principal: $100
Time : 1 year
Rate: 5% or 0.05
 i = prt
 i = 100 * 1 * 0.05 = 5.
 payment = principal + interest
         = 100 + 5
         = $105

Can I develop an algorithm?

I maintain that this is hard since we don't know how to program.
Let's write instructions for a person to do this.
- We will use terms like ask, compute using, tell....
A first pass
- ```
calculate the interest for the loan.
            
```
- This is probably too high level.
- It really doesn't say anything just restates the problem.
A second pass
- ```
Get input
Compute result
Print output
```
- This is probably useless as well.
- This probably solves 70% of all problems.
- It really lacks detail.

Try again

Get principal
Get time
Get rate
output principal, rate, time
compute interest = principal * rate * time
payment = principal + interest
output interest and payment

Given these instructions can you run the test case?
This looks good to me.

one last try

#include <iostream>
#include <iomanip>

using namespace std;

int main() {
   float principal{0},
         interest{0},
         rate{0},
         time{0},
         payment{0};

   cout << fixed << setprecision(2);

   cout << "Enter the principal: ";
   cin >> principal;
   cout << endl;

   cout << "Enter the interest rate: ";
   cin >> rate;
   cout << endl;

   cout << "Enter the time: ";
   cin >> time;
   cout << endl;

   interest = principal * rate * time;
   payment = interest + principal;

   cout << "Principal: $" << principal << endl;
   cout << "Rate: " << rate  << "%" << endl;
   cout << "Time: " << time  << " years" << endl;
   cout << "Interest: $" << interest << endl;
   cout << "Payment: $" << payment << endl;

   return 0;
}

Can you read this?
This is code, which IS an algorithm, but not useful for our purposeses here.

Write the program