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CMSC 150 LOOPS CS 150: Fri 20 Jan 2012
CMSC 150LOOPS
CS 150: Fri 20 Jan 2012
Representing DNA
AGTCCAGTGTCAA
Start Codon: ATG
Start Codon: ATG
Consider in JavaString dna = “AGTCCAGTGTCAA”;
Consider in JavaString dna = “AGTCCAGTGTCAA”;
if ( dna.substring(0,3).equals(“ATG”) )
String dna = “AGTCCAGTGTCAA”;
if ( dna.substring(0,3).equals(“ATG”) )if ( dna.substring(1,4).equals(“ATG”) )
Consider in Java
String dna = “AGTCCAGTGTCAA”;
if ( dna.substring(0,3).equals(“ATG”) )if ( dna.substring(1,4).equals(“ATG”) )if ( dna.substring(2,5).equals(“ATG”) )
Consider in Java
Consider in JavaString dna = “AGTCCAGTGTCAA”;
if ( dna.substring(0,3).equals(“ATG”) )if ( dna.substring(1,4).equals(“ATG”) )if ( dna.substring(2,5).equals(“ATG”) )if ( dna.substring(3,6).equals(“ATG”) )if ( dna.substring(4,7).equals(“ATG”) )...if ( dna.substring(10,12).equals(“ATG”) )
Loops
Loop Syntax
while ( condition ) {
statement; }
for ( initialization; condition; update )
{
statement; }
Loop Syntax
while ( condition ) {
statement; }
for ( initialization; condition; update )
{
statement; }
Use while when you
don’t know in advance
the # of times to loop
Loop Syntax
while ( condition ) {
statement; }
for ( initialization; condition; update )
{
statement; }
Use for when you know in advance the # of times to
loop
While Loop Syntax while ( condition ) {
statement_to_execute; }
build a condition that eventually becomes false need statement w/in body to advance toward false
condition evaluated each time before executing statement
While Loop Example while ( condition ) {
statement_to_execute; }
int count = 0; while ( count < 3 ) { System.out.println( “count = “ + count); count++;}
While Loop Actionint count = 0;
while ( count < 3 )
{System.out.println( “count = “ + count );count++;
}
1. initialize count to 0
While Loop Actionint count = 0;
while ( count < 3 )
{System.out.println( “count = “ + count );count++;
}
1. initialize count to 02. evaluate condition: count < 3 is true, so…
While Loop Actionint count = 0;
while ( count < 3 )
{System.out.println( “count = “ + count );count++;
}
1. initialize count to 02. evaluate condition: count < 3 is true, so…3. execute statement: prints count = 0
While Loop Actionint count = 0;
while ( count < 3 )
{System.out.println( “count = “ + count );count++;
}
1. initialize count to 02. evaluate condition: count < 3 is true, so…3. execute statement: prints count = 04. execute statement: increment count to 1
While Loop Actionint count = 0;
while ( count < 3 )
{System.out.println( “count = “ + count );count++;
}
1. initialize count to 02. evaluate condition: count < 3 is true, so…3. execute statement: prints count = 04. execute statement: increment count to 15. evaluate condition: count < 3 is true, so…
While Loop Actionint count = 0;
while ( count < 3 )
{System.out.println( “count = “ + count );count++;
}
1. initialize count to 02. evaluate condition: count < 3 is true, so…3. execute statement: prints count = 04. execute statement: increment count to 15. evaluate condition: count < 3 is true, so…6. execute statement: prints count = 1
While Loop Actionint count = 0;
while ( count < 3 )
{System.out.println( “count = “ + count );count++;
}
1. initialize count to 02. evaluate condition: count < 3 is true, so…3. execute statement: prints count = 04. execute statement: increment count to 15. evaluate condition: count < 3 is true, so…6. execute statement: prints count = 17. execute statement: increment count to 2
int count = 0;
while ( count < 3 )
{System.out.println( “count = “ + count );count++;
}
While Loop Action
1. initialize count to 02. evaluate condition: count < 3 is true, so…3. execute statement: prints count = 04. execute statement: increment count to 15. evaluate condition: count < 3 is true, so…6. execute statement: prints count = 17. execute statement: increment count to 28. evaluate condition: count < 3 is true, so…
int count = 0;
while ( count < 3 )
{System.out.println( “count = “ + count );count++;
}
While Loop Action
1. initialize count to 02. evaluate condition: count < 3 is true, so…3. execute statement: prints count = 04. execute statement: increment count to 15. evaluate condition: count < 3 is true, so…6. execute statement: prints count = 17. execute statement: increment count to 28. evaluate condition: count < 3 is true, so…9. execute statement: prints count = 2
int count = 0;
while ( count < 3 )
{System.out.println( “count = “ + count );count++;
}
While Loop Action
1. initialize count to 02. evaluate condition: count < 3 is true, so…3. execute statement: prints count = 04. execute statement: increment count to 15. evaluate condition: count < 3 is true, so…6. execute statement: prints count = 17. execute statement: increment count to 28. evaluate condition: count < 3 is true, so…9. execute statement: prints count = 210. execute statement: increment count to 3
int count = 0;
while ( count < 3 )
{System.out.println( “count = “ + count );count++;
}
While Loop Action
1. initialize count to 02. evaluate condition: count < 3 is true, so…3. execute statement: prints count = 04. execute statement: increment count to 15. evaluate condition: count < 3 is true, so…6. execute statement: prints count = 17. execute statement: increment count to 28. evaluate condition: count < 3 is true, so…9. execute statement: prints count = 210. execute statement: increment count to 311. evaluate condition: count < 3 is false, so exit the loop
For Loop Syntax for ( initialization; condition; update
) {
statement_to_execute; }
typically declare and initialize a variable for the loop: int count = 0;
executed exactly once, as loop starts
For Loop Syntax
build a condition based on the loop variable thateventually becomes false
count < 3;
evaluated each time before executing statement
for ( initialization; condition; update )
{ statement_to_execute; }
For Loop Syntax
statement that advances the condition toward failure count = count + 1
executed each time after executing statement
for ( initialization; condition; update )
{ statement_to_execute; }
For Loop Example for ( initialization; condition; update ) {
statement_to_execute; }
for ( int count = 0; count < 3; count++ ) {
System.out.println( "Count = " + count );
}
for ( initialization; condition; update ) {
statement_to_execute; }
for ( int count = 0; count < 3; count++ ) {
System.out.println( "Count = " + count );
}
For Loop Example
for ( initialization; condition; update ) {
statement_to_execute; }
for ( int count = 0; count < 3; count++ ) {
System.out.println( "Count = " + count );
}
For Loop Example
For Loop Actionfor ( int count = 0; count < 3; count++ )
System.out.println( "Count = " + count );
1. initialize count to 0
{}
For Loop Actionfor ( int count = 0; count < 3; count++ )
System.out.println( "Count = " + count );
1. initialize count to 02. evaluate condition: count < 3 is true, so…
{}
For Loop Actionfor ( int count = 0; count < 3; count++ )
System.out.println( "Count = " + count );
1. initialize count to 02. evaluate condition: count < 3 is true, so…3. execute statement: prints Count = 0
{}
For Loop Actionfor ( int count = 0; count < 3; count++ )
System.out.println( "Count = " + count );
1. initialize count to 02. evaluate condition: count < 3 is true, so…3. execute statement: prints Count = 04. update: increment count to 1
{}
For Loop Actionfor ( int count = 0; count < 3; count++ )
System.out.println( "Count = " + count );
1. initialize count to 02. evaluate condition: count < 3 is true, so…3. execute statement: prints Count = 04. update: increment count to 15. evaluate condition: count < 3 is true, so…
{}
For Loop Actionfor ( int count = 0; count < 3; count++ )
System.out.println( "Count = " + count );
1. initialize count to 02. evaluate condition: count < 3 is true, so…3. execute statement: prints Count = 04. update: increment count to 15. evaluate condition: count < 3 is true, so…6. execute statement: prints Count = 1
{}
For Loop Actionfor ( int count = 0; count < 3; count++ )
System.out.println( "Count = " + count );
1. initialize count to 02. evaluate condition: count < 3 is true, so…3. execute statement: prints Count = 04. update: increment count to 15. evaluate condition: count < 3 is true, so…6. execute statement: prints Count = 17. update: increment count to 2
{}
For Loop Actionfor ( int count = 0; count < 3; count++ )
System.out.println( "Count = " + count );
1. initialize count to 02. evaluate condition: count < 3 is true, so…3. execute statement: prints Count = 04. update: increment count to 15. evaluate condition: count < 3 is true, so…6. execute statement: prints Count = 17. update: increment count to 28. evaluate condition: count < 3 is true, so…
{}
For Loop Actionfor ( int count = 0; count < 3; count++ )
System.out.println( "Count = " + count );
1. initialize count to 02. evaluate condition: count < 3 is true, so…3. execute statement: prints Count = 04. update: increment count to 15. evaluate condition: count < 3 is true, so…6. execute statement: prints Count = 17. update: increment count to 28. evaluate condition: count < 3 is true, so…9. execute statement: prints Count = 2
{}
For Loop Actionfor ( int count = 0; count < 3; count++ )
System.out.println( "Count = " + count );
1. initialize count to 02. evaluate condition: count < 3 is true, so…3. execute statement: prints Count = 04. update: increment count to 15. evaluate condition: count < 3 is true, so…6. execute statement: prints Count = 17. update: increment count to 28. evaluate condition: count < 3 is true, so…9. execute statement: prints Count = 210. update: increment count to 3
{}
For Loop Actionfor ( int count = 0; count < 3; count++ )
System.out.println( "Count = " + count );
1. initialize count to 02. evaluate condition: count < 3 is true, so…3. execute statement: prints Count = 04. update: increment count to 15. evaluate condition: count < 3 is true, so…6. execute statement: prints Count = 17. update: increment count to 28. evaluate condition: count < 3 is true, so…9. execute statement: prints Count = 210. update: increment count to 311. evaluate condition: count < 3 is false, so exit the loop
{}
What happens?for ( int count = 0; count > 3; count++ )System.out.println( "Count = " + count );
{}
What happens?for ( int count = 0; count > 3; count++ )System.out.println( "Count = " + count );
{}
What happens?for ( int count = 0; count < 10; count = count++)System.out.println( "Count = " + count );{
}
What happens?for ( int count = 0; count < 10; count = count++)System.out.println( "Count = " + count );
infinite loop!!
because count++ returns value of count before incrementing
{}
What happens?for ( int count = 0; count < 10; )System.out.println( "Count = " + count );
{}
What happens?for ( int count = 0; count < 10; )System.out.println( "Count = " + count );
{}
infinite loop!!
no update, so count is always 0
What happens?for ( int count = 1; count != 10; count += 2)System.out.println( "Count = " + count );
{}
What happens?for ( int count = 1; count != 10; count += 2)System.out.println( "Count = " + count );
{}
What happens?for ( int count = 0; count < 10; count += 2);
System.out.println( "Bill Maher" );{}
What happens?for ( int count = 0; count < 10; count += 2);
System.out.println("Bill Maher" );{}
Prints only once because
of this!
Equivalentfor ( int count = 0; count < 10; count += 2);
System.out.println( "Bill Maher" );{}
for ( int count = 0; count < 10; count += 2) ; // do-nothing statement
System.out.println( "Bill Maher" );
{}
What happens?for ( int count = 0; count < 10; count += 2);
System.out.println( "Count = " + count );
{}
What happens?for ( int count = 0; count < 10; count += 2);
System.out.println( "Count = " + count );
{}
Guess the Number
Start Codon: ATG
While Loop or For Loop?String dna = “ATATGCCTG”;
if ( dna.substring(0,3).equals(“ATG”) )if ( dna.substring(1,4).equals(“ATG”) )if ( dna.substring(2,5).equals(“ATG”) )if ( dna.substring(3,6).equals(“ATG”) )if ( dna.substring(4,7).equals(“ATG”) )if ( dna.substring(5,8).equals(“ATG”) )if ( dna.substring(6,9).equals(“ATG”) )
String dna = “ATATGCCTG”;
if ( dna.substring(0,3).equals(“ATG”) )if ( dna.substring(1,4).equals(“ATG”) )if ( dna.substring(2,5).equals(“ATG”) )if ( dna.substring(3,6).equals(“ATG”) )if ( dna.substring(4,7).equals(“ATG”) )if ( dna.substring(5,8).equals(“ATG”) )if ( dna.substring(6,9).equals(“ATG”) )
While Loop or For Loop?
Building A For LoopString dna = “ATATGCCTG”;
for ( ???????; ???????; ??????? ){if ( dna.substring(i,i+3).equals(“ATG”) ){
// do something magical}
}
Building A For LoopString dna = “ATATGCCTG”;
for ( ???????; ???????; ??????? ){if ( dna.substring(?,?).equals(“ATG”) ){
// do something magical}
}
String dna = “ATATGCCTG”;
for ( ???????; ???????; ??????? ){if ( dna.substring(?,?).equals(“ATG”) ){
// do something magical}
}
Building A For Loop
String dna = “ATATGCCTG”;
for ( int i = 0; ???????; ??????? ){if ( dna.substring(?,?).equals(“ATG”) ){
// do something magical}
}
Building A For Loop
String dna = “ATATGCCTG”;
for ( int i = 0; i < 7; ??? ){if ( dna.substring(?,?).equals(“ATG”) ){
// do something magical}
}
Building A For Loop
String dna = “ATATGCCTG”;
for ( int i = 0; i <= dna.length()-3; ????? ){if ( dna.substring(?,?).equals(“ATG”) ){
// do something magical}
}
Building A For Loop
String dna = “ATATGCCTG”;
for ( int i = 0; i <= dna.length()-3; ????? ){if ( dna.substring(?,?).equals(“ATG”) ){
// do something magical}
}
Building A For Loop
String dna = “ATATGCCTG”;
for ( int i = 0; i <= dna.length()-3; i++ ){if ( dna.substring(?,?).equals(“ATG”) ){
// do something magical}
}
Building A For Loop
String dna = “ATATGCCTG”;
for ( int i = 0; i <= dna.length()-3; i++ ){if ( dna.substring(i,i+3).equals(“ATG”) ){
// do something magical}
}
Building A For Loop
if ( dna.substring(0,3).equals(“ATG”) ) …
if ( dna.substring(1,4).equals(“ATG”) ) …
if ( dna.substring(2,5).equals(“ATG”) ) …
if ( dna.substring(3,6).equals(“ATG”) ) …
if ( dna.substring(4,7).equals(“ATG”) ) …
if ( dna.substring(5,8).equals(“ATG”) ) …
if ( dna.substring(6,9).equals(“ATG”) ) …
for ( int i = 0; i <= dna.length()-3; i++ )
{
if ( dna.substring(i,i+3).equals(“ATG”) ){
// do something magical
}
}
Building A For Loop
for ( int i = 0; i < 7; i++ )
{
if ( dna.substring(i,i+3).equals(“ATG”) ){
// do something magical
}
}
Write An Equivalent While Loop
Digital Images
Digital Images
for ( int row = 0; row < image.getNumRows(); row = row + 1 ){
for ( int col = 0; col < image.getNumCols(); col = col + 1 ){
image.getPixelAt( row, col ).brightenByAmt( 10 );}
}
0
1
2
3
0 1 2 3
Digital Images
for ( int row = 0; row < image.getNumRows(); row = row + 1 ){
for ( int col = 0; col < image.getNumCols(); col = col + 1 ){
image.getPixelAt( row, col ).brightenByAmt( 10 );}
}
0
1
2
3
0 1 2 3
• row = 0, col loops through values 0…3• row = 1, col loops through values 0…3• row = 2, col loops through values 0…3• row = 3, col loops through values 0…3
