review
1. multiple if
In the case of a condition triggered when three or more
if (<Condition 1>) {
1 // condition is true run
} Else if (<Condition 2>) {
// Condition 1 is false, to run true condition 2
} Else if (<Condition 3>) {
// conditions 1 and 2 are false, Condition 3 is running true
}else{
// run-time conditions are false, 2, 3
}
2.switch structure
switch (<integer expression>) {
case 1:
// integer result of the expression to run 1
break;
case 2:
// integer result of the expression to run 2
break;
....
default:
Run-time did not match the results of an integer expression //
}
3. The advantages and disadvantages of various structures
1) if a range determined by multiple
2) contour is determined by switch
4. cyclic structure
1) What is the cycle
Repeatedly run the same or similar code
2) Why use cycle
Reduce code redundancy , improve the maintainability of the program
3) elements of the cycle
3.1) loop variable
3.2) cycling conditions
3.3) Operation cycle
3.4) variable update
5.while cycle
while (<condition>) {
// condition is true when you run code
}
notes
1 generates a random number
1.1) java.util.Random import;
1.2)Random ran=new Random();
1.3) generates integer
int XXX = ran.nextInt (<random range>);
xxx value is possible
0 ~ random range -1
E.g. ran.nextInt (10)
Possible values is 0 to 9,
2.do-while loop
grammar
do{
// condition is true when you run code
} While (<condition>);
3.while and do-while differences loop
1) while loop:
First determine , after execution
Initial conditions are not met , do not perform a
2) do-while loop:
First execution after judgment
Initial conditions are not met , will be performed at least once
3) When understood, understood as:
while loop than do-while loop
More than one judge
4.for cycle
1) for loop syntax
for (Expression 1; 2 Expression; Expression 3) {
// loop
}
1.1)
Expression 1: Declare variables
Expression 2: cycling conditions
Expressions update variables: 3
1.2)
Expression , 2, 3, can be omitted
Expression 2 is omitted defaults to true
However, two ; can be omitted
1.3)
Expression 1 can declare multiple variables,
With , separated
Expression 3 can update multiple variables
With , separated
1.4) for the processing loop for
Cycles cycles fixed
The cyclic structure Summary
1) determining the number of cycles used for
2) the number of cycles of use uncertain
while或do-while
2.1) when the time ......
Use while
2.2) until the time .....
Use do-while
6. The circulation flow control
1) break keyword
The terminating switch can break switch structure
The cyclic structure break can terminate the loop structure
while, do-while, for all you can use
2) continue keyword
It can only be used in a loop structure
Cycle operation to continue the effect that:
Over code is not running the current cycle
Continue to run the next cycle
7. nested loop
1) What is the nested loop
A loop structure
Also contains another complete cycle structure
2) loop nests Notes
2.1) one cycle of the outer loop
Memory cycle cycle again
2.2) flow control keywords (break, continue)
In the inner loop
It affects only the inner loop
2.3)while\dowhile\for
Can be arbitrarily nested
2.4) Any cyclic nesting level
You should avoid excessive levels of nesting
operation
1) in accordance with the off-season season ticket prices,
First class and economy class fees,
Enter the original ticket, month and 1 first class or economy class 2,
In which the high season ( May to October)
First 10%, 15% economy class,
Off-season ( November through April)
First 7 fold, 65 fold economy class,
The final output of ticket prices
Scan = Scanner new new Scanner (System.in); System.out.println ( "Please enter the Ticket Price" ); Double . Price = scan.nextDouble (); System.out.println ( "Please enter the month" ); int month The = scan.nextInt (); System.out.println ( "class' (2. 1. First Economy)" ); int level = scan.nextInt (); // season IF (month The> =. 5 && month The <= 10) { // First IF (Level ==. 1 ) { . price * = 0.9 ; } the else {// economy . Price * = 0.85 ; } } the else { // season IF (Level ==. 1) { // First . Price * = 0.7 ; } the else { . Price * = 0.65 ; } } System.out.println ( " ticket price after the discount is: "+ price);
do-while
1) using a do-while loop to write
Xiao Ming first month's salary 4000
Last month, a month later than 200
Calculate the 12-month total Xiaoming how much they will get wages
int sum=0; int i=1; int sal=4000; do { sum+=sal; sal+=200; i++; }while(i<=12); System.out.println(sum);
2) prepared using the do-while loop
Xiao Ming first month's salary 4000
Last month, a month later than 200
When Bob got a total of more than wages
150000 number of months needed
int i=1; int sum=0; int sal=4000; do { sum+=sal; System.out.println("sum:"+sum+",i:"+i+",sal:"+sal); sal+=200; i++; }while(sum<150000); System.out.println(i-1);
Exercises for loop
1) User input 5 student achievement in the loop
Calculate their average
Scan = Scanner new new Scanner (the System.in); int SUM = 0 ; for ( int I =. 1; I <=. 5; I ++ ) { System.out.println ( "Please enter" + i + "grade students' ) ; int Score = scan.nextInt (); SUM + = Score; } Double AVG = SUM * 1.0 /. 5 ; System.out.println ( "average:" + avg);
break
1) write a loop tips:
The user input cycle while (true) {
If the user inputs a digital ... while (true) {
The number is negative }
End of the cycle
Scan = Scanner new new Scanner (the System.in); // user input negative loop exits the while ( to true ) { System.out.println ( "Enter a number" ); int NUM = scan.nextInt (); IF (NUM <0 ) { // NUM is less than zero, exit BREAK ; } }
2) write a loop
Loop user inputs the password ( int type )
If the user input is 123456 (right)
End of the cycle
And output cycle several times
Scan = Scanner new new Scanner (the System.in); int I =. 1 ; do { System.out.println ( "Please enter the password" ); int pwd = scan.nextInt (); // correct password loop exits IF (pwd = 123456 = ) { BREAK ; } System.out.println ( "wrong password, to re-enter" ); I ++ ; } the while ( to true ); System.out.println ( "total input" + i + "views");
Nested loop
1) use of nested loops to achieve the output
Multiplication table
for(int i=1;i<=9;i++) { for(int j=1;j<=i;j++) { System.out.print( j+"×"+i+"="+i*j+" "); } System.out.println(); }