Midterm 2 Solution

CS 17

1. Short Answer Problems. Each of the following problems is worth 35 points.
   1. For a function, define declaration, definition, call, actual parameter, and formal parameter.
      • Declaration --- Also known as the prototype. The function name, return type, and number and types of parameters are made known to the compiler.
      • Definition --- Where the details of the function are given; that is, the function's code is here.
      • Call --- Where the function is used. Control is transferred from the calling function to the called function.
      • Actual parameter --- A parameter associated with the function call. It may be any valid expression of the appropriate type.
      • Formal parameter --- A parameter associated with the definition of the function. It is a local variable of the function, initialized from the value of the corresponding actual parameter.

   2. For the following questions, assume the following declarations:

      int i = 1;
      int j = 2;
      int k = 3;
      double x = 1.0;
      double y = 2.0;
      double z = 3.0;
      

      1. Parenthesize this expression and write its value:

         i + j == k;
         
         ((i + j) == k);   ==> 1
         

      2. Parenthesize this expression and write its value:

         k - i < y > x;
         
         (((k - i) < y ) > x);   ==> 0
         

      3. Parenthesize this expression and write its value:

         z - x + 1 != j + k - 2 * i;
         
         (((z - x) + 1) != ((j + k) - (2 * i)));   ==> 0
         

      4. What are the definitions of the values true and false in C++?

         Any non-zero value is interpreted as ``true.'' Zero is interpreted as ``false.''

   3. What is printed by the following program?

      #include <iostream.h>
      
      int a, b, c;
      
      void f1(void);
      void f2(void);
      
      int main()
      {
         int a;
      
         a = 5;
         b = 3;
         c = 7;
      
         cout << a << " " << b << " " << c << endl;
         f1();
         cout << a << " " << b << " " << c << endl;
      
         return 0;
      }
      
      int d = 4;
      
      void f1(void)
      {
         int c = 10;
      
         a = 3;
         b++;
      
         cout << a << " " << b << " " << c << " " << d << endl;
         f2();
         cout << a << " " << b << " " << c << " " << d << endl;
      }
      
      void f2(void)
      {
         int d = 45;
      
         a += 4;
         b = 7;
         c = d + a;
         cout << a << " " << b << " " << c << " " << d << endl;
      }
      

      Each output value was worth 1.5 points. Here's the output:

      5 3 7
      3 4 10 4
      7 7 52 45
      7 7 10 4
      5 7 52
      

2. Programming Problems. Each of the following problems is worth 35 points. You are more likely to receive partial credit if you write your code so that I can understand what you've done.
   1. Write a function for computing the number of ways in which r objects from be selected from a set of n objects (choose(n, r)). Here is the mathematical definition:

      

      The parameters n and r are integers. The function should return an integer value. Your function should make use of a factorial function, which you are also to write. Here is the definition of :

      

      and are defined to have the value 1. Again, n is an integer. The function should return an integer value.

      // Prototypes.
      int fact(int);
      int choose(int, int);
      
      
      int fact(int n)
      {
         int prod = 1;
      
         while (n > 1)
         {
            prod *= n;
            --n;
         }
      
         return prod;
      }
      
      
      int choose(int n, int r)
      {
         return fact(n) / (fact(n - r) * fact(r));
      }
      

   2. Write a function printFloat() with four formal parameters: number, width, fill, and precision, which prints a floating-point value, number, in scientific notation, right-adjusted in a field of width width with a fill character of fill, and a precision of precision.

      void printFloat(double number, int width, char fill, int precision)
      {
         cout << setw(width) << setfill(fill) << setprecision(precision)
              << setiosflags(ios::scientific) << setiosflags(ios::right)
              << value;
      }