population

Population Growth

Determine how long it takes for a population to reach a particular size.

$ ./population
Start size: 100
End size: 200
Years: 9

Populations

Say we have a population of n llamas. Each year, n/3 new llamas are born, and n/4 llamas pass away.

For example, if we were to start with n = 1200 llamas, then in that year, 1200/3 = 400 new llamas would be born and 1200/4 = 300 llamas would pass away. At the end of that year, we would have 1200 + 400 - 300 = 1300 llamas.

As another example, if we were to start with n = 1000 llamas, at the end of the year, we would have 1000/3 = 333.33 new llamas. We can't have a decimal portion of a llama though, so we'll truncate the decimal to get 333. 1000/4 = 250 llamas will pass away, so we'll get a total of 1000 + 333 - 250 = 1083 llamas at the end of the year.

Implementation Details

Complete the implementation of population.c at right, such that it calculates the number of years required for the population to grow from the start size to the end size.

• The program prompts the user for two numbers. To prompt the user, we use the get_int() function, which takes in a message as its argument. This function, when called, will print the specified message and return the value that the user inputs into the system.
• We've stored the values returned by the get_int() function inside variables named start and end, both having the int data type. start and end represent the numbers of llamas we're starting with and ending with.
• Your program should first ensure that the start size is greater than or equal to 9—if we start with less, the population of llamas will quickly become stagnant! It should prompt the user to enter another value for as long as this condition is not met.
• Your program should then ensure that the end size is greater than the start size. It should prompt the user to enter another value for as long as this condition is not met.
• Your program should then calculate an integer number of years until the end value is reached. Remember that there cannot be a decimal number of llamas at the end of each year.
• Finally, your program should print the number of years required for the llama population to reach that end size.

Hints

• To create a new variable, make sure to specify a data type, a name for the variable, and what value it should be assigned to. It might help to take a look at how the variables start and end are created.

• You might find a while loop helpful to you. Remember that a while loop works as follows: while a certain condition evaluates to true, execute these particular commands. Stop when the condition no longer evaluates to true.

  while(condition)
  {
      //commands to execute;
  }

How to Test Your Code

Your program should behave per the examples below.

$ ./population
Start size: 1200
End size: 1300
Years: 1

$ ./population
Start size: -5
Start size must be at least 9.
Start size: 3
Start size must be at least 9.
Start size: 9
End size: 5
End size must be greater than start size.
End size: 18
Years: 8

$ ./population
Start size: 20
End size: 1
End size must be greater than start size.
End size: 10
End size must be greater than start size.
End size: 100
Years: 20

$ ./population
Start size: 100
End size: 1000000
Years: 115

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