Abstract Data Types

Data Types in C++

• primitive data types (e.g., int, bool, float)
• user-defined data types (e.g., string)
• data type
  • domain of values
  • operations

Structuring Data in C++

• collection of data variables under a common name
• unlike an array, a
  AخA

   

  struct
  can hold variables of different types
• introduces a new type into the program
• definition syntax
  ​x

   

  struct identifier {

      variable declaration;

      //variable declaration 1;

      //variable declaration 2;

      //...

  };
• variables in a
   

  struct
  are called members
• access members through dot operator (.)
   

  identifier.member;
• initialization
   

  struct_name var_name = {value0, value1, value2, ... };
• Example
   

  struct Student {

      string name;

      int test_grades[3];

  };

  ​

  Student John;

  John.name = "John";

  John.test_grades[0] = 95;

  John.test_grades[1] = 84;

  John.test_grades[2] = 92;

  ​

  Student Mary = {"Mary", {88, 93, 99} }

Fraction example

•  

  #include <iostream>

  using namespace std;

  ​

  /**

   * gcd(a, 0) = a

   * gcd(a, b) = gcd(b, a mod b)

   */

  int gcd(int a, int b)

  {

      if (b==0)

          return a;

      return gcd(b, a%b);

  }

  ​

  /**

   * lcm = (a*b)/gcd(a,b)

   */

  int lcm(int a, int b)

  {

      auto local_gcd = gcd(a,b);

  ​

      if (local_gcd == 0)

          return 0;

      return a / gcd(a,b) * b;

  }

  ​

  void add(int num_1, int den_1, int num_2, int den_2, int& result_num, int& result_den)

  {

      result_den = lcm(den_1, den_2);

      result_num = num_1*(result_den/den_1) + num_2*(result_den/den_2);

  }

  ​

  int main()

  {

      int num_1 = 1;

      int den_1 = 2;

  ​

      int num_2 = 1;

      int den_2 = 3;

  ​

      int result_num;

      int result_den;

  ​

      add(num_1, den_1, num_2, den_2, result_num, result_den);

  ​

      cout << result_num << "/" << result_den << endl;

  ​

      return 0;

  }

In-Class Modifications to fraction Example

•  

  #include <iostream>

  using namespace std;

  ​

  /**

   * gcd(a, 0) = a

   * gcd(a, b) = gcd(b, a mod b)

   */

  int gcd(int a, int b)

  {

      if (b==0)

          return a;

      return gcd(b, a%b);

  }

  ​

  /**

   * lcm = (a*b)/gcd(a,b)

   */

  int lcm(int a, int b)

  {

      auto local_gcd = gcd(a,b);

  ​

      if (local_gcd == 0)

          return 0;

      return a / gcd(a,b) * b;

  }

  ​

  struct Fraction

  {

      int numerator;

      int denominator;

  };

  ​

  Fraction operator+(Fraction lhs, Fraction rhs)

  {

      auto common_den = lcm(lhs.denominator, rhs.denominator);

  ​

      Fraction rtn;

      lhs.numerator = lhs.numerator * common_den/lhs.denominator;

      rhs.numerator = rhs.numerator * common_den/rhs.denominator;

  ​

      rtn.numerator = rhs.numerator + lhs.numerator;

      rtn.denominator = common_den;

      return rtn;

  }

  ​

  ostream& operator<<(ostream& ostm, const Fraction& frac)

  {

      ostm << frac.numerator << "/" << frac.denominator;

      return ostm;

  }

  ​

  int main()

  {

      Fraction f1 = {1,2};

      Fraction f2 = {1,3};

  ​

      Fraction result = f1 + f2;

  ​

      cout << f1 << " + " << f2 << " = " << result << endl;

  ​

      return 0;

  }