Loops

Chapter 7: Loops

Looping constructs:

for (count-controlled)
while (condition-controlled)
do/while

Sections 7.1-7.3

A bit of a hodge-podge of examples.

Counting and summing variables:

Loop counters in "for"
The accumulators total and totalvalid in program 5
sum1.cpp.
count1.cpp.

while:

  while(condition)
  {
     statements
  }

Example of a loop that is not count-controlled (fixed-step):

  eat dinner
  while (there is a dirty dish)	
     wash one dish			
  do homework

Ch7 starts with fixed step loops where you count how many times it it executed.
Printing hello 5x:

Counting by 3:

These are fixed-step. Exit condition is solely determined by the counter final value.

Using chars as loop counters: 1, 2.

Pitfall: generating an infinite loop when you don't mean to.
What is happening here:

   while (count <=10)
     cout << "hello";
     count++;

   while (count <=10);  //a silent infinite loop
   {
     cout << "hello";
     count++;
   }

inf1.cpp inf2.cpp

Is an infinite loop ever a good idea?
Yes, the keyboard operates this way.

  while (true)
  {
     read next keystroke
     process it
  }

Section 7.4

For loops to input groups of data.
(some review)

sum1.cpp finds the sum of 10 numbers
How do we add just the positive numbers? sum2.cpp
How do we find the average? add avg to it: avg1.cpp
The average of the positive numbers: avg2.cpp.
Suppose I want sum2 to run for a user-specified #: sum3.cpp

Section 7.5

More on designing for loops: finding a maximum: 1, 2.

Section 7.6 While versus Do

   do{ 
     statements
   }
   while (condition)

do.cpp

7.7 User-controlled data with while and do..while loops

findsum.cpp: uses a sentinal
receipts.cpp (needed for assignment 7, simpler logic but clunkier since you have to type y each time).

7.8 Debugging Strategies

insert extra cout
debugger (built-in, not very friendly)
hand tracing