Programming Language Concepts

Week 3: Constants in Programming

Overview of Programming Languages

• Various programming languages mentioned include:

  • Microsoft Language Pascal

  • DATATRIEVE

  • ALGOL PL

  • SALSA ATS

  • Assembly, ELAN, Fancy SuperTalk, ABC

  • C++, GM Constraint, XOTd, de Cayenne, Oxygene

  • PEARL, BUSS, notation, Cyclone, TACPOL, shell, Visual

  • Go, ABAP, C/AL, Cg

  • Rust, GDL, Bistro, JOSS, PT, Co Scale, Genie

  • Inform, Sense Talk, Blue, HAL/S, SIMSCRIPT, Revolution, Sawzall, Chapel

  • Agora, Clojure, Ajax, Not Trac, Adenine, A+

  • Object, Rapira, CSKA, SIMPLE, Autolt, Microcode

  • Lynx, SAM76, Redcode, language LispVB, JavaScript

  • Delphi, DASL, Script, PHP, Common, ORCA/Modula-2

  • Arc, Moby, Uniface, Caral, WATFOR, Eustisp

  • ObjectScript, D, R, Forth, GameMonkey, MicroScript

  • Logo, Squirral, Windows/Dos, Kaleidoscope, IMP

  • Newapeak, b, T, Caml, Z, Prolog, JASS

  • Java, Programming, Ruby, EXEC, RPG, CorVision

  • Action, REXX, NETO, Simula, Python

  • Strand, Robot, SP/k, Boomerang, COBOL

  • GraphTalk, Turing, ISWIM, Haxe, Eiffel

  • S/SPL/SQL, A, Chuck

Lecture 2 Recap: Key Concepts

• High vs low level language

• Structure of a C program

  • Example: "Hello World" program

• C Basic Syntax

• Variables and their definitions

• Basic input and output

C Program Structure

• A C program generally consists of the following parts:

  • Preprocessor Commands

  • Functions

  • Variables

  • Statements & Expressions

  • Comments

C Basic Syntax

Variables

• Definition: A variable is a name given to a storage area that programs can manipulate. It is a symbolic representation of a memory location.

• Composition: Variable names can be comprised of letters, digits, and the underscore character and must start with a letter or underscore. C is case-sensitive, treating upper and lowercase letters distinctly.

Hello World Example

#include <stdio.h>
int main() {
    /* my first program in C */
    printf("Hello, World!\n");
    return 0;
}

Today's Lecture

• Focus: C Basic Syntax, Data Types, Constants

Data Types in C

• Data types are essential for declaring variables or functions of various types—determining space in storage and interpretation of the bit pattern.

• C allows creating numerous distinct types derived from four fundamental data types:

  • Integer

  • Character

  • Float

  • Double

Qualifiers in C

• Qualifiers modify base data types:

  • Sign Qualifiers (Signed/Unsigned)

  • Size Qualifiers (Long/Short)

Sign Qualifiers

• Both integers and floating-point variables can hold negative and positive values.

• Use of signed or unsigned types:

  • Example: unsigned int student_id; // Will not store negative numbers

• Storage ranges for a signed integer:

  • 4 bytes: from -2^{31} to 2^{31}-1

• Storage for an unsigned integer:

  • 4 bytes: from 0 to 2^{32}-1

Size Qualifiers

• Alters the size of basic types:

  • Long: largest range of signed values.

  • Example: long int memory_address;

  • Short: limited range of signed values.

  • Example: short int day_of_week, week_of_year;

• Guarantees: The size of a short type is smaller than long. The rationale for short qualifiers is memory conservation. Calculations on long types are slower than on short types.

Standard Integer Types

Standard Floating-Point Types

Character Data Type

• Keyword: char is used for character type variables

  • Example: char test = 'h'; // test is a character variable with the value 'h'

• Size of char: 1 byte.

Constants

Definition and Characteristics

• A constant is a data item storing a fixed value that cannot be altered during execution.

• Characteristics:

  • Both constants and variables share types.

  • Can be declared as:

  • Integer constant

  • Floating constant

  • Double constant

  • Character constant

• Best Practice: Use upper-case names for constants.

Defining Constants

• Constants can be defined via two methods:

  • Using #define preprocessor:

  • Format: #define identifier value

    • Example: #define YEAR 2020

  • Using the const keyword:

  • Format: const type variable = value;

    • Example: const int YEAR=2020;

Types of Constants

• Primary Constants: Integer, Real, Character

• Secondary Constants: Array, Pointer, Structure, Union, Enum, etc.

Integer Constants

• Whole numbers that can be: positive, zero, or negative.

• Integer constants specified in:

  • Decimal: e.g., 1234, 255

  • Octal: starts with 0, e.g., 0377

  • Hexadecimal: starts with 0x or 0X, e.g., 0xFF, 0x4B

  • Suffix can be included for unsigned or long.

Examples of Integer Constants

85   /* decimal */
0213 /* octal */
0x4b /* hexadecimal */
30   /* int */
30u  /* unsigned int */
30l  /* long */
30ul /* unsigned long */

Integer Constants: Example Code

#include <stdio.h>
int main() {
    const int SIDE = 10; // constant declared
    int area;
    area = SIDE * SIDE; // using constant
    printf("The area of the square with side: %d is: %d sq. units", SIDE, area);
    return 0;
}

Floating-Point Constants

• Structure:

  • An integer part

  • A decimal point

  • A fractional part

  • An exponent part

• Representation:

  • Decimal form: must include decimal point or exponent.

  • Exponential form: signed exponent introduced by e or E.

Examples of Floating-Point Constants

3.14159
314159E-5L
510E2
.e55     // Illegal: incomplete exponent

Example Using Constant:

#include <stdio.h>
#define PI 3.14159 // defined constant for PI
int main() {
    float earth_radius = 6378.1; // earth radius float
    int circumference = 2 * PI * earth_radius;
    printf("The circumference of planet earth is: %d km", circumference);
    return 0;
}

Character Constants

• Enclosed in single quotes (e.g., 'x').

• Can represent:

  • Plain character

  • Escape sequence (e.g., '\t')

  • Universal character (e.g., '\u02C0')

Escape Sequences