[General] Switch case doubt help

[varunme]

can we write a switch case statement as below?

char uart_rd;

switch (uart_rd )       // If data is received,
    {

	case 1:  char sequence[3]={0b11000011,0b11011011,0b11100011};
	case 2:  char sequence[3]={0b11000011,0b11111011,0b11100011};
	case 3:  char sequence[3]={0b11000011,0b11011011,0b11100011};
	case 4:  char sequence[3]={0b11010011,0b11011011,0b11110011};
    }

 

[betwixt]

I don't see why not. If 'uart_rd' is known value at the point of entry and you can place any valid instructions in each 'case' statement.

Things to watch for are:
1. what happens if uart_rd is NOT 1, 2, 3, or 4. Should you have a 'default:' to trap other values.
2. you might want to put a 'break' instruction after each 'case' line. Some compilers will wastefully check all the following lines for a match, some will skip them.

Brian.

 

[FvM]

2. you might want to put a 'break' instruction after each 'case' line. Some compilers will wastefully check all the following lines for a match, some will skip them.

If the compiler behaves according to the C specification (I hope, it does), the code execution will proceed downwards til a break statement or end of the switch construct. The switch expression works like a computed goto, the next case label doesn't change the execution flow.

you can place any valid instructions in each 'case' statement.

There are various syntax errors involved with the shown code:
- the case label must preceed a statement, not a variable declaration
- repeating a declaration within the same scope (e.g. code block) isn't allowed
- a declaration in the middle of a code block is C++ style and might be unsupported by the compiler

 

[betwixt]

I took that as being two sections of code, the declaration somewhere earlier and the switch statement inside main() or another function, just placed together in the example so we could see what kind of variable 'uart_rd' is. I take the point that 'sequence[]' should be declared earlier and it's value modified if necessary in the switch statement. I think if the language is C++ the redeclaration would be allowed, even if it would be pointless to do so.

I agree a 'break' is a good idea, some compilers will automatically insert one as part of the code optimization but adding one manually will always work.

Brian.