CSE240 Lecture 05

Introduction to Programming Languages
Data, Data types and Type Checking
(202201)

Transcript

1. jgs
   CSE 240
   Introduction to Programming Languages
   Lecture 05: Data, Data types and Type Checking
   Dr. Javier Gonzalez-Sanchez
   javiergs@asu.edu
   javiergs.engineering.asu.edu | javiergs.com
   PERALTA 230U
   Office Hours: By appointment
   

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2. Javier Gonzalez-Sanchez | CSE240 | Spring 2022 | 2
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   Data | Memory management
   

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3. Javier Gonzalez-Sanchez | CSE240 | Spring 2022 | 3
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   Data Types
   § A set of primary values allowed and operations on these values.
   § Data types define size and format – used to declare variables.
   // Java
   int (4) (-231 to 231 ) ; -2,147,483,648 to 2,147,483,647
   float (4) 3.4e−038 to 3.4e+038
   

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4. Javier Gonzalez-Sanchez | CSE240 | Spring 2022 | 4
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   Data Types
   § A set of primary values allowed and operations on these values.
   § Data types define size and format – used to declare variables.
   00000000000000000000000000000011
   int i = 3;
   01000000010000000000000000000000
   float j = 3.0f;
   sign exponent fraction
   

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5. Javier Gonzalez-Sanchez | CSE240 | Spring 2022 | 5
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   Type Checking (semantic)
   § Ensuring that the types of operands of an operator are legal or equivalent to
   the legal type.
   "Hello" + 5;
   5 > 7 + “Hello”
   char x = 60 + 5;
   float a = 2.0;
   double b = 2.0;
   int b = 'a';
   

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6. Javier Gonzalez-Sanchez | CSE240 | Spring 2022 | 6
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   Data Types Equivalence (Complex Types)
   § Structural equivalence
   Two types are equivalent if they have the same set of values and
   operations.
   § Name equivalence
   Two types are equivalent if they have the same name
   

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7. Javier Gonzalez-Sanchez | CSE240 | Spring 2022 | 7
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   Data Types Equivalence (Complex Types)
   class Foo {
   int data[100];
   int count;
   }
   class Bar {
   int data[100];
   int count;
   }
   Foo x, y;
   Bar r, s;
   // name
   // equivalence
   // correct
   x = y;
   r = s;
   // incorrect
   x = r;
   // structural
   // equivalence
   // correct
   x = y;
   r = s;
   // correct
   x = r;
   

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8. Javier Gonzalez-Sanchez | CSE240 | Spring 2022 | 8
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   Type Conversion
   § Coercion –implicitly convert Type_A to Type_B.
   § Casting: –explicitly convert Type_A to Type_B.
   § Type error.
   

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9. Javier Gonzalez-Sanchez | CSE240 | Spring 2022 | 9
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   Type Conversion
   int x = 5;
   // Coercion: Implicit type conversion (int to float)
   float f = 3.14f + x;
   // Casting: Explicit type conversion (float to int)
   int i = (int) f + x;
   

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10. Javier Gonzalez-Sanchez | CSE240 | Spring 2022 | 10
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    Strong Type Checking
    A strongly typed language is one in which:
    § each name in a program has a single type associated with it;
    § the type is known at compilation time;
    § type errors are always reported.
    Strong
    Weak
    C C++ Java
    

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11. Javier Gonzalez-Sanchez | CSE240 | Spring 2022 | 11
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    Strong Type Checking
    A strongly typed language is one in which:
    § each name in a program has a single type associated with it;
    § the type is known at compilation time;
    § type errors are always reported.
    Is strong type checking good?
    ☐ Yes
    ☐ No
    ☐ Maybe
    

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12. Javier Gonzalez-Sanchez | CSE240 | Spring 2022 | 12
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    Strong Type Checking
    A strongly typed language is one in which:
    § each name in a program has a single type associated with it;
    § the type is known at compilation time;
    § type errors are always reported.
    Is strong type checking good?
    Trade flexibility for reliability!
    Strong type increase reliability,
    but it loses the flexibility.
    float x = 3.0f; // Java
    float x = 3.0; // C
    (defvar x 3.0) // LISP
    

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13. Javier Gonzalez-Sanchez | CSE240 | Spring 2022 | 13
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    Questions
    

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14. jgs
    Coming next
    Programming with C and the Structural Paradigm
    

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15. jgs
    CSE 240 Introduction to Programming Languages
    Javier Gonzalez-Sanchez, Ph.D.
    javiergs@asu.edu
    Spring 2022
    Copyright. These slides can only be used as study material for the class CSE240 at Arizona State University.
    They cannot be distributed or used for another purpose.
    

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