In an IF condition statement, a logical condition can only have one, and if there are multiple conditions, it can be resolved using nested IF statements, but this method increases the complexity of the program and reduces the readability of the program.
Using the switch Process Control statement can solve these problems perfectly, with the following basic structure:
Switch statement syntax
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switch (conditional expression) { Case constants: { Statement A; } Case constants: { Statement B; } Case constants: { Statement C; } ... Case constants: { Statement F; } Default { Statement N; } } |
Switch statement Syntax description
Sequentially executes each statement following the case, and then executes the statement n below the default
The statements that follow each case can be multiple, but use {} to include
The values behind each case must be different.
Where A is a numeric or character type data, the value of A is A1, A2 、...... In comparison, if a is equal to one of the values, the statement following the corresponding data is executed, and when the keyword break is encountered, the program jumps out of the switch structure and executes the statement below the keyword default if a value equal to a is not found.
Switch Case statement:
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var year=8; var army= "", msg= ""; Switch (parseint (year)) { Case 0: army= "Civilians"; Break Case 1: Army= "PVT"; Break Case 2: Army= "first-class soldier"; Break Case 3: Case 4: Case 5: Army= "First Class Petty Officer"; Break Case 6: Case 7: Case 8: Army= "Level two Petty officer"; Break Default if (year>8) Army= "senior Petty Officer"; } msg+= "Soldiers:" +year+ "year n"; msg+= "Conclusion:" +army; Alert (msg); |
Example
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var a = 3; Switch (a) { Case 0: { document.write ("www"); } Case 1: { document.write ("Dreamdu"); } Case 2: { document.write ("com"); } Case 3: { document.write ("Www.111cn.net"); } Default { document.write ("Http://www.111cn.net"); } } |
Results
Www.111cn.net
Http://www.111cn.net
Complete SWITCH statement syntax
The results above are usually not what we want, and if you execute a statement after a case, you should jump out of the switch statement, which is the true switch multiple-branch selection statement. You can add a break (jump) after each branch, and the following section describes the break.
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switch (conditional expression) { Case constants: { Statement A; } Break Case constants: { Statement B; } Break Case constants: { Statement C; } Break ... Case constants: { Statement F; } Break Default { Statement N; } } |
When the value of an expression is equal to a constant following a case, the statement executed after the constant is executed, then the switch branch selection statement is executed, and the statement n after the default is performed when all the constants after the case do not conform to the expression.
Example
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var a = 3; Switch (a) { Case 0: { document.write ("www"); } Break Case 1: { document.write ("Dreamdu"); } Break Case 2: { document.write ("com"); } Break Case 3: { document.write ("Www.111cn.net"); } Break Default { document.write ("Http://www.111cn.net"); } } |
Look at this function:
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function Selectartiletype (typenum)//typenum is an argument passed in {
Switch (typenum) { Case "0"://When typenum== "0" document.getElementById ("C_1"). style.display= "None"; document.getElementById ("c_2"). style.display= ""; Break Case "1"://When typenum== "1" document.getElementById ("C_1"). style.display= ""; document.getElementById ("c_2"). style.display= "None"; Break Case "2"://When typenum== "2" document.getElementById ("C_1"). style.display= ""; document.getElementById ("c_2"). style.display= ""; Break Default "3"://any other value document.getElementById ("C_1"). style.display= "None"; document.getElementById ("c_2"). style.display= "None"; Break } } |