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Slide 1
Dr. Yang, Qingxiong (with slides borrowed from Dr. Yuen, Joe)
LT4: Control Flow - Loop CS2311 Computer Programming
Slide 2
Outlines 2 While and Do While loop For loop
Slide 3
Outcomes 3 Able to express repeating task with a loop statement
in C++ Clearly define the loop condition and loop body
Slide 4
Syntax Summary 4 Keywords while, do, for Punctuators,
Slide 5
Loop 5 Beside sequential execution and branch execution,
looping is another common control flow in programming. When the
execution enters a loop, it will execute a block of code repeatedly
until the exit loop condition is matched
Slide 6
Loop 6 In general, a program loop consists of: Initialization
statements Body Exit condition Post loop statements (stepping
forward to exit loop condition)
Slide 7
Loop 7 Set x=0; cout 10) then exit the loop Add 1 to X Loop
back
Slide 8 > n; while (n > x; /* read 1st number */ max = x;
/* pick the largest number in while-loop */ while (++cnt < n) {
cin >> x; /* read another number */ if (max < x) max = x;
} cout
An example program of while (contd) 9 cout > x; /* read 1st
number */ max = x; /* pick the largest number in while-loop */
while (++cnt < n) { cin >> x; /* read another number */ if
(max < x) max = x; } cout
Example of do statement 11 int error; /* no Boolean type
support */ int n; do { cout > n; if (error = (n 1 and m1 and m1
and m> n">
break statement 19 the break statement causes an exit from the
innermost enclosing loop or switch statement (discussed already)
while (1) { cin >> n; if (n < 0) break; /* exit loop if x
is negative */ cout
Example of continue statement 21 /* read in and sum 10
not-too-small numbers. */ cnt = 0; while (cnt < 10) { cin
>> x; if (x > -0.01 && x < 0.01) continue; /*
discard small values */ ++cnt; sum += x; /* continue transfer
control here */ }
Slide 22
Continue, break 22
Slide 23
Comma operator (,) 23 q It has the lowest precedence of all
operators in C++ and is evaluated from left to right q General form
is expr1, expr2 q The comma expression as a whole has the value and
type of its right operand Sometimes used in for statements to allow
multiple initializations and multiple processing of indices q The
comma operator is rarely used q Not all commas in a C++ program are
comma operators
Slide 24
Examples of comma operator 24 sum=0; for (j=1; j> true; /*
print true */ else cout >> false; Use (2 < k && k
< 7) for the correct answer
Slide 27
Further remarks 27 q Use a relational expression, if possible,
rather than an equality expression to control a loop or a selection
statement, e.g., Don t use while (j!=4) {... } Use while (j
Programming style 29 Follow the normal rules of English (e.g.
putting a space after a comma) Put one space on each side of a
binary operator (e.g. = > < ) for readability Indent code in
a consistent fashion to indicate the flow of control (use the tab
key) Note the multiple levels of indentation
Slide 30
Indentation 30 void main(){ int i; for (i = 0; i < 100; i++)
{ if (i>3) cout