Contents

cs201/07

Previous

Study pages 121-132

3.6 The While loop

Syntax 3.3 While Statement

while_statement::="while" "(" condition ")" statement.
Informal example 1
```
 		while(some ice cream left)
```
```
 			eat a spoonful;
```
Informal example 2
```
 		while(not full)
```
```
 		{
```
```
 			eat ice cream;
```
```
 			get some more ice cream;
```
```
 		}
```
Example from text [ 02exalg.cpp ]
Semantics
```
 		while(A) B
```
executes the statements like this
```
 		A; B; A; B; ... until !A
```
Common Error 3.6 Infinite loops

Common Error 3.7 Off-by-one Errors

3.7 The for Loop
Use for all situations that involve counting! And many other situations as well
Syntax 3.4 for Statement
for_statement::= "for" "(" initialization ";" condition ";" update ") statement.
```
 		for( int i=1; i<=10; i++) s=s+i;
```
Informal example
```
 		for( number_of_bottles=99; number_of bottles > 0; number_of_bottles--)
```
```
 			drink bottle of beer;
```
Count the semicolons.
Semantics
```
 		for(A; B; C) D
```
executes the statements like this
```
 		A; B; D; C;  B; D; C; B; D; C; B; D; C; ... until !B
```
It does precisely the same thing as
```
 		{  A;
```
```
 		   while(B)
```
```
 		   {
```
```
 		       D
```
```
 		       C;
```
```
 		   }
```
```
 		}
```
Quality Tip 3.3 Use for loops for their intended purpose
Use for loops to count!
Quality Tip 3.4 Don't use != to test for the end of a numeric range
Notice however that in the next Common error an != is used because the loop is not counting items up to a particular value but searching a string for a particular value -- and this means we have to use "!=".
Common Error 3.8 Forgetting a semicolon

Quality Tip 3.5 Symmetric and asymetric Bounds

Quality Tip 3.6 Count Iterations to get the bounds

3.8 The do loop
I don't like this... but you can use it if you like.
Syntax 3.5 do statement
do_statement::="do" statement "while" "(" condition ")" ";".
The do loop
```
 		do A while (B);
```
executes
```
 		A; B; A; B; ... until !A
```
and is the smae as
```
 		A;
```
```
 		while(B)
```
```
 			A
```
Boolean Loops
We hardly ever need to write loop where a bool variable goes from 'false' to 'true' and then stops. Writing
```
 		for(bool p = false; p != true; p=!p)
```
does not work! (Think about it).
So in the rare cases when we need to do this try
```
 		for(int count=0; count <=1; count++)
```
```
 		{   bool p = (count == 1);
```
```
 		    ...
```
```
 		}
```

Review Questions

R3.15, 3.16, 3.17, 3.18, 3.20 3.21 3.22 3.23, 3.24, 3.25, 3.26, 3.27
Exercises on loops and logic
Fibbonaci revisited This code [ 05ex.cpp ] only does a few terms in the series and is very repetitive. Recode it to use a while loop, and continue while f3 is less than or equal to 100.
Example of developing a program with a loop [ E_(mathematical_constant) ]
1. Clarify problem
2. Write an algorithm
3. Walk through the algorithm and correct any logic errors
4. Code in C++
5. while( compiler gives errors )
  1. Fix compile error
6. while( bugs show up )
  1. Debug code
7. Run code
Example of a quizlike While loop [ while0.cpp ]
Project 3 Due Next time from chapter 3 with if statements

Quiz 3 tracing a program with strings next time

Lab 04 -- Logic
[ lab04/ ]
Next -- advanced looping
[ 08.html ]

Abbreviations

Algorithm::=A precise description of a series of steps to attain a goal, [ Algorithm ] (Wikipedia).
Class::=A description of a type of object that includes the data it knows and the functions it can execute.
Function::programming=A selfcontained and named piece of program that knows how to do something.
Gnu::="Gnu's Not Unix", a long running open source project that supplies a very popular and free C++ compiler.
OOP::="Object-Oriented Programming", Current paradigm for programming.
Semantics::=Rules determining the meaning of correct statements in a language.
SP::="Structured Programming", a previous paradigm for programming.
Syntax::=The rules determining the correctness and structure of statements in a language, grammar.
Q::software="A program I wrote to make software easier to develop",
TBA::="To Be Announced", something I should do.
TBD::="To Be Done", something you have to do.
UML::="Unified Modeling Language", industry standard design and documentation diagrams.
void::C++Keyword="Indicates a function that has no return value".

( End of document ) <<Contents | Top