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The CONST definition

The CONST definition. CONST Pi = 3.14159, City = ‘New York’; Constant identifiers are used when you do not want the value of an identifier to change why not just put the value in the program?

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The CONST definition

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  1. The CONST definition • CONST Pi = 3.14159, City = ‘New York’; • Constant identifiers are used when you do not want the value of an identifier to change • why not just put the value in the program? • Note: The compiler automatically defines the type to the constant identifier by looking at the value assigned to it.

  2. Reserved words • Certain words have special meaning to the compiler. Therefore these words cannot be used as constant or variable identifiers. • We have seen some examples: • DIV, MOD • VAR, CONST • PROGRAM, BEGIN, END

  3. String Variables • Note: This is not part of the Pascal standard. It was added to Turbo Pascal (and some other Pascal compilers) • To declare a string variable we could write: • VAR Country: string[13]; • To assign a value to a string variable we could write: • Country := ‘United States’;

  4. More about integers • What if you need an integer larger than 32767? • Using integer type would be incorrect • another type called LongInt is used • -2147483648 -> 2147483647 • other integer types are: • byte (0->255) • shortint (-128->127) • word (0->65535)

  5. More about reals • Reals also have other types • real 6 bytes 11 to 12 digits • single 4 bytes 7 to 8 digits • double 8 bytes 15 to 16 digits • extended 10 bytes 19 to 20 digits

  6. Chapter 3 topics • write / writeln • readln • VAR declaration • CONST definition • assignment statement (including arithmetic)

  7. Formatting output: integers • Field: a group of columns in which results are printed is called a field • Field width: The number of columns in the field • writeln(IntId:##) • IntId is an integer identifier or value • ## is the rightmost column to print the integer (Compiler will ignore this value if its smaller than number of digits) • can be written as any integer expression • default is one

  8. Formatting output: reals • Writeln (RealId:#1:#2) • RealId is a real identifier or value • #1 is the rightmost column to print the real • #2 is the number of digits you want on the right of the decimal point. • If #2 is omitted, scientific notation is used

  9. Formatting output: strings • Writeln (stringId:##) • stringId can be a string or character identifier or value • ## is the rightmost column for the string to be printed in

  10. Formatting output: Boolean • Similar to strings • note: Although the compiler is not Cap sensitive, it always prints Boolean values in all CAPS.

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