Lecture 12 - October 4^th

Discussed the completed outlines submitted.

Talked a little about chapter 5

Discussed the grading of the output produced by your programs

Talked about static and dynamic scope rules

what variables are known where under each type of rule

Discussed the importance of using the term non-local rather than global for variables not declared in a given program block.

Beginning of Chapter 5 outline

Chapter 5 is really about Identifiers (i.e. variables and constants)

Identifiers

• names issues

• length
• case sensitivity
• key or reserved words
• name forms
• writability problems
• keyword is special only in certain contexts
• reserved words may not be used as identifiers
• required first character type
• other allowable characters
• before FORTRAN90 names could have spaces which were ignored
• variables
• what are they?
• cell or collection of cells
• what are their attributes?
• name
• address
• what is it
• machine memory address with which it is associated
• same name may be associated with different addresses dependent on where it occurs in a program (subprograms)
• same name may be associated with different addresses dependent on when it occurs in a program (stack)
• l-value
• aliases
• C and C++ union types
• pointers
• subprogram parameters
• type
• determines range of values
• determines operations that can be performed
• value
• physical contents of memory cell or cells associated with the variable
• abstract contents of memory cell
• r-value
• lifetime
• how long is it resident in memory?
• scope
• where in the program is it known?