- The syntax and
meaning of the
while, for
and do-while
in C++ are
identical to
that of Java
- We don't need to discuss the
these
statements
- The remainder of the notes is a refresher in case you have forgotten it...
- while loop: will execute the loop body
0 or more times
- for loop: is actually a specialized while loop.
This loop will execute the loop body 0 or more times
- do loop: will execute the loop body 1 or more times
- Syntax
while ( Boolean expression ) one-statement
while ( Boolean expression ) { more-than-one-statement } - Semantic: (its meaning)
- Evaluate the Boolean expression
- If Boolean expression is TRUE, then
execute the WHILE Body and repeat the
WHILE statement again
- If Boolean expression is FALSE, then the WHILE statement is completed and execution continue at the statement following the WHILE statement
- Evaluate the Boolean expression
- Important note:
The statements in the while body MUST affect the boolean condition (or else, the while loop will never end - infinite loop....)
- Syntax
for ( initialization; boolean expression; update ) one-statement
for ( initialization; boolean expression; update ) { more-than-one-statement } - Semantic: (its meaning)
- Executes the initialization
part
- Then evaluate the Boolean expression
- If Boolean expression is TRUE, then:
- execute the FOR Body and after this,
- execute the update part and after this,
- repeat the FOR statement again
- If Boolean expression is FALSE, then the FOR statement is completed and execution continue at the statement following the FOR statement
- Executes the initialization
part
- A FOR statement can
ALWAYS be replaced
by a WHILE loop as follows:
for ( initialization; boolean expression; update ) statement
initialization; while ( boolean expression ) { statement update; } - Example: sum an array
A is an integer array of 10 elements
sum = 0; for ( i = 0; i < 10; i = i + 1 ) sum = sum + A[i];
sum = 0; i = 0; while ( i < 10 ) { sum = sum + A[i]; i = i + 1; }
- Synatx
do one-statement while ( boolean expression )
do { more-than-one-statement } while ( boolean expression ) - Semantic: (its meaning)
- Executes the DO body (statement)
part
- Then evaluate the Boolean expression
- If Boolean expression is TRUE, then
repeat the DO statement again
- If Boolean expression is FALSE, then the DO statement is completed and execution continue at the statement following the DO statement
- Executes the DO body (statement)
part
- A DO statement can
ALWAYS be
replaced
by a WHILE loop as follows:
do statement while ( boolean expression )
statement while ( boolean expression ) { statement } - NOTE: We have to duplicate
the statement part...
- NOTE: Do loops are rarely used....
- Problem:
Given 2 integer numbers a and b , find their greatest common divisor GCD - Often, the computer can solve a problem
using the
brute force search
approach - because it can perform billions of
multiplications in a second; it can search much more
rapidly than humans can.
As long as the search space is limited , the brute force search is often the best way to solve a problem with a computer.
- The brute force approach to finding GCD:
The GCD is a number between 1 and a - test every number between 1 and a !!!
Given: a and b for (i = 1; i <= a; i = i + 1) if ( a divisible by i AND b divisble by i ) GCD = i; - C/C++ program for GCD:
#include <iostream.h> int main() { int a, b, i, GCD; a = 96; b = 256; GCD = 1; for ( i = 1; i < a; i = i + 1) { if ( (a % i == 0) && (b % i == 0) ) { GCD = i; } } cout << GCD << endl; }
- Example Program:
(Demo above code)
- Prog file: click here
How to compile and run:
Compile: CC -o GCD GCD.C Run: GCD
- Problem:
Given 2 integer numbers a and b , find their least common multiple LCM - The brute force approach to finding LCM is as follows:
The LCM is a number between a and a*b - but you can exit as soon as you find the first one.
Given: a and b i = a; while ( i not divisible by a OR i not divisible by b ) i = i + 1; // Try next number LCM = i;
- C/C++ program for GCD:
#include <iostream.h> int main() { int a, b, i, LCM; a = 96; b = 256; i = a; // First number to try while ( (i % a != 0) || (i % b != 0) ) { i = i + 1; // Try next number... } LCM = i; cout << LCM << endl; }
- Example Program:
(Demo above code)
- Prog file: click here
How to compile and run:
Compile: CC -o LCM LCM.C Run: LCM