4. Common Facilities of Programming Languages

4. Common Facilities of Programming Languages

1. output data

   • screen- Text, graphs, Graphics
   • Printer- same as screens, need to say which line is going to be printed first and the page size, Printer.print "text"
   • File- fixed length, delimited- seperated by character

2. operators

   • arithmetic operators
     • '+'- add, '-' - subtract, '*'- multiply, '/'- divide, '^' exponentiation (power..)
     • C#: 'MOD' - finds the remainder, 'DIV' - divides two numbers ignores remainder
   • relational operators
     • pseudo code '='-equals, '<'-less than, '<='-less than or equal to, '>'-more than, '>='-more than or equal to,'<>'-not equal to
     • C#- '==' equal, '!=' not equal to
   • boolean operators
     • and-assigns values as false unless both are true, pseudo 'AND', C#- '&'
     • or- assigns values as true unless both are false pseudo 'OR', C#- '||'
     • not-only one value, just assigns the opposite to the imputed value, pseudo 'NOT', C#- '!'

3. String manipulation

   • LOCATE(str1,str2)- finds the start position of str1 in str2
   • LEFT(str,n)- returns the first n characters of str, can do it to find the last n characters if RIGHT is used instead of LEFT
   • MID(str,m,n)- returns n number of characters in str starting at the m character
   • LENGTH(str)- returns number of characters in str
   • each character is stored a binary digits, ASCII- 7 binary digits and 8th parity, ANSI- used by most modern computers- uses 8 bits- more characters stored- not only latin script
   • ASCII(ch)- changes 'ch' into its equivalent ASCII equivalent, CHAR(n)- changes teh value n in ASCII into its character equivalent
   • Concatenation- '+' or '&' to join two strings together

4. using operators

   • all operators are done from left to right unless there are brackets
   • arithmetic: 5+6-3=11-3=8 Logical:TRUE AND NOT FALSE OR TRUE =>TRUE AND TRUE OR TRUE =>TRUE OR TRUE =>TRUE
   • example: a=3 b=4........ (5 – a) * (b + 1) > (a * b – 6)=> 2*5 > 12-6 => 10 >6=> TRUE

5. comparing strings

   • It changes the character into the ASCII code equivalent
   • order of characters: Numbers, Uppercase, lowercase
   • Numbers stored as strings: the computer looks at first value on the left and then the right, e.g. comparing 2 and 17- 1 is smaller than 2 so 17<2

6. input and validate data

   • Validation- checking against rules already defined by computer- sensible data
   • Verification- checks data against the original
   • Format check:

7. assignment statements

   • it takes the form of 'variable = expression'
   • the right side is looked at the first before the left side so that it assigns the left side to the night side

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