Include data table in design. This should give a valid variable declaration that states its type. Choose an identifier. this should reflect the purpose of the variable.

Identifiers - parameters

• Up to 32 characters (compiler will not recognise any more than 32).
• Begin with a letter
• Subsequent characters - letters, underscore and digits 0-9
• Identifiers are case sensitive
• Keywords cannot be identifiers

Main variable types

• Integers i.e. whole numbers - positive or negative. Integer division always rounds towards zero e.g. (11/4)=2 - actually 2.75 rounded to 0. (-11/4)=-2 for reasons as above.
• Real Numbers - digits either side of decimal point. Positive or negative. Any size you like! Floating Point - 5.9743000000E2 where 5 is the mantissa and the 2 is the exponent.
• Characters - as laid out in the ASCII table.
• Strings - a sequence of characters.
• Boolean variables - true or false. This will depend on the condition of the expression.

More to come on these - I think!

Loops - Extend the four number mean program to read in fifty numbers. Let the machine do the counting using a loop expression. (A repeated sequence) a top level design would be:

1. set up loop
2. loop while there are more numbers
3. process next number
4. loopend
5. determine mean value

The count starts at zero. On every loop test for count = 50. One is added to the count for every loop. If count = 50 loopend - if not then loop.

Type	Identifier	Description
Integer	Count	Counts the numbers that are input
Integer	Total	Records the total value of the numbers that are input
Integer	NextNumber	The next number to be input
Real	Mean	The output value of total divided by fifty

Count must be initialised to 0. Total must be initialised to 0.

What happens if there are an undetermined number to be input? One solution is to provide a sentinel value. A predetermined signal to end the loop. This is dependent on the user knowing the sentinel value! Program must prompt for input of the sentinel value to terminate the program.

Testing - Format of the if step -

• if condition then
• action for then branch
• else
• action for else branch
• ifend

The if step

if (condition)
{
	statement 1;
	statement 2;
	...;
}
else
{
	statement 1;
	statement 2;
	...;
}

• The word then is not in C++, it is only used in design.
• Condition in brackets () is any boolean expression.
• then and else are delimited by braces {} (if more than one statement) containing C++ statements (then clause and else clause).
• Many if steps require else action of nothing - omit keyword else and statement.
• More than two statements are a compound statement.
• A compound statement is always in braces with no semi-colon after the final brace.

The while step

while (condition)
	{ single or compound statement }

• Condition in brackets (), is any boolean expression giving true or false results.
• Loop body is a single or compound statement.
• As with if-else a compound statement is always in braces with no semi-colon after the final brace.

C++ Code for extended Mean

//---------------------------------------------------------------------------

#pragma argsused
int main(int argc, char* argv[])
{
int Count;
int Total;
int NextNumber;
float Mean;
        Count = 0;
        Total = 0;
        NextNumber = 0;
                while(NextNumber != -1)
        {
                        NextNumber = ReadIntPr("Enter next number or -1 to stop: ");
                        if(NextNumber != -1) //Do not put a semi-colon here!
                        {
                        Total = Total + NextNumber;
                        Count = Count + 1;
                        }
        }
                Mean = float(Total)/Count;
                WriteFloatPr("The mean value is ", Mean);
                getchar();
        return 0;
}
//---------------------------------------------------------------------------

The above code section includes: if statement, while statement and a sentinel value.

Attention to correct syntax is crucial. If the line:

if(NextNumber != -1)

was to be followed by a semi-colon, the program would compile and run, but the results would be totally wrong.

The code below was a practical exercise to design and code to measure sequence lengths in coin tosses. I did'nt get it right first time! I missed out this section and a corresponding closing brace further down.

if (Toss != 'Q')
{

The code compiled and ran but seemed to count the 'Q' to Quit as an extra in the Total giving a wrong result.

int main(int argc, char* argv[])
{
int SequenceNumber;
int Total;
char LastToss;
char Toss;
float Mean;
        SequenceNumber = 0;
        Total = 0;
        Toss = 'Z';
        LastToss = 'Z';
                while(Toss != 'Q')
        {
                Toss = ReadCharPr("Enter next toss H or T (or Q to Quit): ");
                if (Toss != 'Q')
                {
                        Total = Total + 1;
                        if (Toss != LastToss)
                        {
                        SequenceNumber = SequenceNumber + 1;
                        LastToss = Toss;
                        }
                }
        }
                Mean = float(Total)/SequenceNumber;
                WriteFloatPr("The mean sequence length is ", Mean);

        getchar();
        return 0;

Comments, suggestions, ideas to
Stuart Banner