1. Basic Debugging (compilation)
Compiler errors
occur when a program has incorrect syntax/construction
messages may be cryptic, but…
line numbers (where the error occurred) are provided
Start on the line identified in the first error
note: it may actually be before the listed line
fix that error, then recompile
sometimes errors cascade from an earlier error
more than one error may disappear!

2. Functionality
OK, program compiles and runs, but it’s wrong – now what?
Insert diagnostic output statements
using cout
at locations where you suspect things are going wrong or other critical points in the code
beginning and end of functions
after complex calculations
to display intermediate results, e.g. variables affected by each major algorithm step
Remove extra output statements when problem is solved
or use // to “comment them out”

3. Another Debugging/Testing technique
Use a compiler directive or a variable to activate print statements
Avoids have to comment out print statements – just set/unset the variable, but…
It has runtime overhead: the if statement always gets executed…
// this goes at the top of the file (set to 0 to turn it off)
#define DEBUG 1
or, as a global
const DEBUG=1; …
// example: somewhere in the file a random function…
void somefunction() {
If(DEBUG) { cout << “entered somefunction()…” << endl; }
… function statements … }

4. Common Programming Errors
Omitting braces ( { })
Omitting a closing brace ( } )
Misuse of = for ==
Missing statement end “;”