A. Function Specifications

1. func

   Additional problems (PDF)

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   spec -- Function specifications. A function specification is a structured description of the behavior of a function, in terms of arguments, return values, etc. For example, the mean function defined by

   double mean(double num1, double num2) {
     return (num1 + num2)/2;
   }
   

   satisfies the following specification:

   mean 2 arguments: double (double-precision floating-point numbers Return: A double, the average value of arg1 and arg2.

   This spec describes the function mean() unambiguously.

   • The number of arguments for that function are indicated, and their types are identified.

   • The return value is described in terms of the argument(s).

   • The spec uses arg1 and arg2 to refer to the individual arguments for that function.

   • The type of the return value is also indicated.

   A spec is often accompanied by one or more example calls, such as

       mean(5, 8) --> 6.5
   

   For another example of a spec, consider the function sum_input() defined by

   int sum_input() {
     int val;  /* holds next integer value from standard input */
     int sum = 0;  /* sum of input integers so far */
     while (scanf("%d", &val) != EOF) 
       sum = sum + val;
     return sum;  
   }
   

   This function has no arguments, but reads values from standard input. Here is a spec:

   sum_input No arguments State change: Integer values are read from standard input, which is assumed to consist only of a series of integer values. Return: A long, the sum of those input integers.

   Example call:

   sum_input()
   

   If the standard input contains

   16 40 20
   82
   

   then the return value will be 158

   • A state change is an effect of a function other than a return value. Input and output (as in sum_input()) are examples of state changes.

   DO THIS:

   Write a program specs.c that

   • includes the two function definitions mean() and sum_input() (these should be entered
     after #include <stdio.h> and before main() );

   • calls mean() with arguments 5 and 8, and prints the return value along with a descriptive label (e.g.,

     The call mean(5, 8) returns 6.5
     

   • Prompts for the user to enter input integers, followed by CTRL/D; and

   • calls sum_input() with standard input

     16 40 20
     82
     

     and prints the return value with a descriptive label (e.g.,

     The return value from calling sum_input() is 158
     

   Note:

   The function sum_input() will read input integers until the end of standard input is detected.

   • When running your program in the usual way at the command line, enter CTRL/D (hold down control key and press D) at the beginning of an input line in order to end standard input for your program ./specs

     ./specs
     16 40 20
     82
     CTRL/D
     

   • Alternatively, you can enter your input integers in a file specs.in, and run your program using this command:

     ./specs < specs.in
     

     In this case, the end of that file specs.in constitutes the end of standard input for that program ./specs .

   To submit your work on this problem, enter these commands:

   git add specs.c
   git add specs.in   # only if you used a file specs.in as described above
   git commit -m "hw4:  problem 1"
   git pull origin master
   git push origin master
   




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For the problems below:
Write C function definitions for each of the following specs, together with main() programs that test that function. For each of these problems marked [HC],

• Write out your function definition and main() on a piece of paper as correctly as possible -- so correct, if possible, that someone else who didn't know C could type it in exactly and produce a correct C computation. If you are uncertain about anything as you write, look it up.

• Then, enter your program, compile, and verify that it runs correctly

• Finally submit your program to stogit using the commit message

  "hw4: problem n"
  

  with the appropriate problem number n.

(Note: Writing out your work by hand precisely beforehand is the most direct way to master the details of C programming. If there are no errors, your understanding of C is confirmed. If there turns out to be an error in your code, that error indicates exactly what you still need to learn about C. Writing out by hand also prepares you for taking quizzes.)
2. areaCircle -- [HC] Area of a circle. In Mathematics, the area of a circle with radius r is .

   Use this formula to implement the following C function.

   area One argument: A non-negative float value, representing the radius of a circle Return: A non-negative float value, the area of a circle of radius arg1

   Example call:

   area(3) --> 28.274333882308138
   

   Hint:

   • You can define a value for π in C as follows:

     const double pi = 3.1415926;  
     

     Here, the type const double means that the variable pi holds a double value and may not be assigned a new value.




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3. moInterest -- [HC] Monthly interest. In Economics, the amount of monthly interest owed on a loan depends on the principal (or amount of money still owed on the loan) and the interest rate. The interest rate r is often expressed as a percentage per year. Thus, the formula for a monthly interest charge on a loan with current principal P is

   Use this formula to implement the following C function.

   moInterest 2 arguments: Non-negative float numbers, a principal amount (of money) and an interest rate (expressed in percent per year) Return: A non-negative float number, the amount of one month's interest on a loan with current principal arg1 at interest rate arg2. .

   Example:

       moInterest(10000, 6) --> 50.0