COMSCI 1101 LEC (MIDTERMS)
UNIT 5: (PART 1)
STATEMENTS
Three basic classifications of statements in C
programming:
 Primitives – simple statements
 Decisions – “Decision Control Structures”
 Loops – iterative statements
Primitive Statement
 These are also known as simple statement.
 A simple statement is composed of an
expression or a function call followed by a
semicolon.
 The other two types of primitives are: null
statement and compound statement.
o The Null statement is made up of a
null expression followed by a
semicolon (a null expression is an
empty expression).
o A compound statement is formed
by placing more than one
statement inside curly braces, { }.
 Syntax of primitive statements
Decision Statement
 Also called as the Decision Control
Structure.
 These statements allows to select and
execute specific blocks of code while
skipping other sections.
 Decision statements are actually part of a
larger category of statements known as
branches.
 Branch statements allow the programmer
to alter the flow of program control.
 C supports two kinds of branch statements
– conditional branches and unconditional
branches.
Decision statements has 2 basic types:
1. Conditional branches – make decision
before branching.
o Single decision branch - if/else
o Multi-decision branch - switch case
2. Unconditional branches – direct program
branching with no decision involved.
o The goto statement is an example of
an unconditional branch.
IF STATEMENT
Expression (condition) is evaluated. If expression is
true (yields a non-zero value), then statement1 is
executed; if expression is false (yields a zero value),
then statement1 is not executed. And continue
executing statement that follows the if statement
(ex. statement2 will then be executed on the
figure).
IF-ELSE STATEMENT
If expression is true, statement1 is executed; if
expression is false, skip statement1 then the else
branch is followed, and statement2 is executed.
And continue executing statement that follows the
if- else statement (ex. statement3 will then be
executed on the figure).
IF-ELSE-IF STATEMENT
In an if-else-if statement, the statement in the elseclause of an if-else block is another if-else structure.
This cascading of control structures enables a
programmer to make more complex selections.
SWITCH CASE
The expression is evaluated and its value is
compared, in turn, to constant A, constant B, etc.
If a match is found at constant A, then all
statements following that case are executed until
a break, or the end of the switch statement is
encountered. If no match is found, then the default
case (if present) is taken.
CODING GUIDELINES
1. Deciding whether to use an if statement or
a switch statement is a judgment call. You
can decide which to use, based on
readability and other factors.
2. An if statement can be used to make
decisions based on ranges of values or
conditions, whereas a switch statement
can make decisions based only on a single
integer or character value. Also, the value
provided to each case statement must be
unique.
3. Unlike with the if statement, the multiple
statements are executed in the switch
statement without needing the curly
braces.
4. When a case in a switch statement has
been matched, all the statements
associated with that case are executed.
Not only that, the statements associated
with the succeeding cases are also
executed. To prevent the program from
executing statements in the subsequent
cases, we use a break statement as our last
statement.
UNIT 5: (PART 1)
Iterative Statement
 One of the fundamental properties of a
computer is its ability to repetitively execute
a set of statements.
 These looping capabilities enable the
programmer to develop concise programs
containing repetitive processes that could
otherwise require thousands of program
statements to perform.
 C contains three looping constructs which
are also called repetition control structures:
o For loop
o While loop
o Do-while loop
for vs. while vs. do-while
 The while() and for() statements may be
described as test-before-execute. If the
controlling condition results initially to a zero
or false value, the body of the loop is never
executed.
 The do-while() statement, on the other
hand, may be considered as executebefore- test. The body of the loop is always
executed at least once.
Properties of Iterative Statements
Initialization
 Initial value of the variable to be evaluated.
Condition
 Evaluated each and every time before the
loop is executed to determine whether the
loop will be executed or not.
Change of state
 Increment or Decrement
Statement
 Executed once the condition is met.
For Loop
 It is the most general looping construct.
 It can merge all the three parts i.e.
assignment, condition checking and
increment/decrementing.
While Loop
 A while loop has one control expression (a
specific condition) and executes as long as
the given expression is true.
 It evaluates the test expression before
every loop, so it can execute zero times if
the condition is initially false.
Do-While Loop
 It is an “upside down” version of the while
loop.
 Here, the loop condition is tested at the
end of the body of the loop.
break and continue Statements
 The statements break and continue are
used to interrupt the normal flow of loops
and the switch statement.
 Sometimes when executing a loop, it
becomes desirable to leave the loop as
soon as a certain condition occurs
(perhaps an error condition).
break Statements
 The break statement ends the loop
immediately when it is encountered.
 The break statement is almost always used
with if...else statement inside the loop.
continue Statements
 The continue statement skips the current
iteration of the loop and continues with the
next iteration.
 continue is the most often used statement
to bypass a group of statements inside a
loop based on some condition:
Unconditional Branch: goto Statement
 Execution of the goto statement causes a
direct unconditional branch to be made to
a specified point in the program.
 The goto statement causes the flow of the
program to branch to the statement
immediately following the appropriate
label.
 A label is a name that is formed with the
same rules as variable names and must be
immediately followed by a colon.