control structures if else do while continue break switch case return for
TRANSCRIPT
Control Structures
if else do while continue break switch case return for
What is the if statement?
"Probable-Possible, my black hen,
She lays eggs in the Relative When.
She doesn't lay eggs in the Positive Now
Because she's unable to postulate how."
-- Frederick Winsor
If examples
• if (age > 65) stopPayingSocialSecurity = true;
if (youAteLotsOfFood)
youGetFat = true;
if (grade < 65)
letterGrade = “F”;
if else examples
• if (grade < 65)letterGrade = “F”;
else if ((grade > 65) && (grade < 70))
letterGrade = “D”;
else if ((grade >= 70) && (grade < 80))
letterGrade = “C”; // etc....
Making If handle multiple statements..
• if (theCowsComeHome) {statement1;
System.out.println(“moo”);
} else {
// this is called a block of code
theOtherThingYouMightDo;
}
Conditional Operator
letterGrade = (grade < 65) ? “F” : “pass”;
Good for assignments with many simple boolean decisions.
The While statement
• Why should I use the while statement?– Do something as long as some condition is met.
• int i = 10;
while ( i >= 0) {
System.out.println(i);
i = i – 1;
}
Sample Output
• 10 9 8 7 6 5 4 3 2 1 0
Do statement
• Why do I need the do statement?
• int i=0;
do {
System.out.println(i++);
} while (!(i > 10));
Do{….} while(In.getBoolean(“continue?”));
while example
• while (userWantsToContinue) {– keepDoingStuff;
• }
• while (weHaveMoreData) {– keepDoingDataProcessing;
• }
Do Example
• do {– promptUserForCommand;
• } while(userInputIsNotQuit);
for statement
• for (init; booleanCondition; iter) {• }• for (int i=0; i <= 10; i++)
System.out.println(i);/// as an alternativeInt i=0; //just like a while….While (i<=10){System.out.println(i++);
}
Continue
continue is a reserved word.
Continue alters the flow of control
Continue must reside in a continue target.
Some continue targets are:
WHILE, DO, FOR, SWITCH
What does continue do?
• Makes the target go to the next value.
for(int i=0; i < 10; i++) {
if (i < 5) continue;
System.out.println(i); // prints 5..9
}
Cont. in While
int i=0;
while (i < 10) {
i++;
if ((i % 2) = =0) continue;
System.out.println(i);
} // 1 .. 9
do continue!
int i=0;
do {
i++;
if ((i % 2) == 1) continue;
System.out.println(i);
} while(i < 10); //2..10
Break
• Break is a Java keyword
• Makes the target terminate.
• Must be in a break target.
• for, while, do, switch
Break example
for(int i=0; i < 10; i++) {
if (i < 5) break;
System.out.println(i); // prints NOTHING
}
while-break
int i=0;
while (i < 10) {
i++;
if ((i % 2) = =0) break;
System.out.println(i);
} // prints 1
do-break
int i=0;
do {
i++;
if ((i % 2) == 1) break;
System.out.println(i);
} while(i < 10); //prints nothing
labeled Continue
start: for (int i=0; i < 10; i++) {for (int j=0; j < 10; j++) {
System.out.println(i+j);
if (i + j > 10) continue start;
}
}//doubly nested for-loop with labeled continue.
labeled break
start: for (int i=0; i < 10; i++) {for (int j=0; j < 10; j++) {
System.out.println(i+j);
if (i + j > 10) break start;
}
}//doubly nested for-loop with labeled break.
// prints 0..9,1..10, 2..11 then stops.
switch statement
• switch – reserved word
• switch – makes a table out of several different statements and selects which ones get executed. Like a complex if-else.
switch(argument)
• argument is byte, char, short, int
• NOT double, float, long or String
Switch Example
int i = 10;
switch(i) {
case 2: {
statement;
break;
}
case 10: {
statement;
break;
}
}
switch on char
char a = ‘q’
switch (a) {
case ‘q’: {
quit();
break;
}
case ‘s’: {
save();
break;
}
}
default
• default is a keyword
• default appears in switch statements
• default is used when no case is satisfied
Example default
char a = ‘z’
switch (a) {
case ‘q’: {
System.out.println(“quit”);
break;
}
default: {
System.out.println(“command not found”);
break;
}
}
return
• return is a reserved word.
• causes a sudden change in the flow of control to the invoking method.
example of return
public static void main(String args[]) {
System.out.println(“this is the return example”);
return;
}
example of return
public static void main(String args[]) {
double x = 10 * Math.cos(Math.PI);
if (x > 20) return;
System.out.println(x);
}
My first method using return
public static int addOne(int x) {return x + 1;
}
public static void main(String args[]) {
System.out.println(addOne(1));
}
degs to rad example
public static double deg2rads(double d) {return d * Math.PI / 180.0;
}
public static void main(String args[]) {
System.out.println(deg2rads(180));
}
F2C
public static double f2c(double f) {return (5.0/9.0) * (f –32);
}
public static void main(String args[]) {
System.out.println(f2c(212));
}
future value of an investment
public static double fv(
double p, double r, double y) {return p * Math.pow(1+r,y);
}
public static void main(String args[]) {
System.out.println(fv(100,0.07,30));
}
return a string
public static String getName() {return “CS131”;
}
public static void main(String args[]) {
System.out.println(getName());
}