Reading Assignment: All of Programming Chapter 2 Reading Code
Learning to read code means that you can execute it by hand in a step-by-step fashion.
2 important parts to executing code by hand:
- understanding what each statement does
- keeping track of the state of the program in a correct fashion
Suggestions on the 1st part: make a “quick reference” sheet.
Variables
Programs track most of their state in variables.
Declaration
Definition of identifier: the name of a variable.
Assignment
Definition of assignment statements: change the value of variables.
Expressions
Definition: a combination of values and operations which evaluates to a value.
Modulus operator ‘%’ is an uncommon operator, which evaluates to the remainder when dividing the first operand by the second.
Variables are taken part in expressions by reading the current value of its box.
The way to solve an algebraic equation:
- write a meaningful assignment statement
- take current value of variables
- update variables
Functions
A function gives a name to a parameterized computation–it is the implementation in code of a specific algorithm. One should declare a function first, which provides the definition for how a function behaves, and calling a function, which executes the definition of the function on specific values of the parameters.
Scope
Definition: The scope of a variable is the region of code in which it is visible. Within a variable’s scope, its name may refer to it. Outside of a variable’s scope, nothing can refer to it directly. In C, the scope of a local variable begins with its declaration and ends at the closing curly-brace(}).
The colored block means the scopes of variables.
If no variables in the scope, the reference is illegal. If exact one variable is mentioned, that is it. If there are multiple variables with the same name, we select the one whose declaration is in the innermost enclosing block. That is, if you went backwards out of blocks, through open curly braces, the variables which would go out of scope first is the one to use.
Try not using global variables for any problems.
Note: The rest of this section talks about the scope of variables by giving an exact example.
Printing
printf function. The last letter f stands for “formatted”
Escape sequences are two (or more) characters, the first of which is a backslash(\), which gives the remaining characters special meaning.
Conditional Statements
In C, an if/else statement specifies the block of code to be executed. Logic Operators and Boolean Operators are of great help to give true or false value.
if/else
switch/case
Shorthand
also called syntactic sugar
2 types:
- a shorter way to write common patterns of existing things, like
x += y - omit the curly braces around single statement block of code, like if
ifstatement is one single statement, the curly braces are not required. But it is hight inadvisable to do so!!
Loops
Loops is a important way to repeat the same block of code multiple times. Another way to repeat is recursion, which will being discussed in Chapter 7.
while Loops
do-while Loops
A while loop may execute the body zero times, skipping the entire loop. By contrast, a do-while loop is guaranteed to executes its body at least once because it executes the loop body before ever checking the condition.
for Loops
Nesting
continue and break
Higher-level Meaning
Except for reading code in a step-by-step fashion, understanding of the meaning of a piece of code is another useful skill. That is the ability to translate the code into the algorithmic step it represents, then figure out what the purpose of that general algorithm is.