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Switch function in C does all the cases
(6 answers)
Closed 3 years ago.
Output:
case0
case1
case2
casedef
I understand that the default case is running because there is no break statement executing inside of the switch statement.
But I don't understand why case 1 and 2 are running when 0!= 1 and 0!=2
Also if I write switch(1) instead of switch(0) then only case 1 and 2 run which is understandable since 1!=0 and 1=1, 1=2 (in boolean? because non zero number denotes truth, but I am not sure, please correct me)
int main(){
switch(0){
case 0: printf("case0\n");
case 1: printf("case1\n");
case 2 : printf("case2\n");
default : printf("casedef\n");
}
}
Switch cases "fall through" to cases that are under them. You're seeing the mentioned behavior because cases for 1, 2 and default are all underneath 0. When you're switching on 1, you see 2 and the default because they're both underneath 1.
If you want to avoid falling through, you need to explicitly break out of the switch at the end of each case:
int main(){
switch(0){
case 0: printf("case0\n"); break;
case 1: printf("case1\n"); break;
case 2 : printf("case2\n"); break;
default : printf("casedef\n"); break;
}
}
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I saw a tutorial that explaining how to use the "break" statement in a loop
but every time i'm trying to use it i'm getting a compilation error saying:
"break statement not within loop or switch
break;"
This is my code:
if (finalFirstChar > 6 || finalFirstChar < 1)
{
printf("You didn't entered a proper number! \n");
break;
}
FWIW, if is a condition (selection statement, to be exact), and break works in a loop (iteration statement)/switch-case statement.
As per C11, chapter ยง6.8.6.3
A break statement shall appear only in or as a switch body or loop body.
In any case, you don't need a break in a if statement body.
OK:
while (cond1) {
if (cond2) break; /* or continue; */
if (cond3) return [something];
}
for (init; cond4; after) {
if (cond5) break; /* or continue; */
if (cond6) return [something];
}
do {
if (cond7) break; /* or continue; */
if (cond8) return [something];
} while (cond9);
if (cond10) return [something];
NOT OK:
if (cond11) { /* not in any while/do/for loop, or case switch */
break; /* or continue; */
}
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I'm working on my latest new function. Any explanations would be great since I'm new to programming. I couldn't figure out how to fix this because the errors I got are:
18 syntax error before '{' token
20 case label not within a switch statement
21 (same as above)
22 (same as above)
23 `default' label not within a switch statement
29 [Warning] `return' with a value, in function returning void
32 [Warning] assignment makes pointer from integer without a cast
34 [Warning] `return' with a value, in function returning void
void moveCar(char board[], char vehicle, char direction, int distance)
{
int i;
int position, newPosition;
int offset;
for (i = 0; i < size; i++) //the main loop for the vehicles and user's input
{
if(isalpha(vehicle))//vehicles for all letters but 'x'
{
if(board[i] == vehicle)//vehicles on board
{
swtich(direction)
{
case 'r': offset = 1; break;
case 'l': offset = -1; break;
case 'u': offset = -8; break;
case 'd': offset = 8; break;
default: printf("invalid direction"); break;
newPosition = position + offset;
if(newPosition != '.')
{
printf("invalid move.");
return 0;
}
board = '.';
board[newPosition] = vehicle;
return 1;
}
}
}
}
It looks like you have a typo of Switch as Swtich, the compiler won't recognize it, and the case statements will fail to compile.
Additionally you close your switch statement too early. If you want those commands to execute only in default move them before the break. If you want them to execute for every case move them outside of the switch statement entirely
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Here i just experienced with the switch command and if command at C. I have omitted the if command by comment and wrote the same command by using switch command. But its now working as i gave the instruction. Where i have mistaken? As i am a learner please pardon my mistakes..
#include <stdio.h>
#include<stdlib.h>
int main()
{
char card_name[3];
puts("enter the card name: ");
scanf("%2s", card_name);
/*int val=0;
if (card_name[0]=='K') {
val=10;
} else if (card_name[0]=='Q'){
val=10;
} else if (card_name[0]=='J'){
val=10;
} else if (card_name[0]=='A'){
val=11;
}else{
val=atoi(card_name);
}*/
int val=0;
switch (card_name[0]) {
case 'K':
case 'Q':
case 'J':
val=10;
break;
case 'A':
val=11;
default:
val=atoi(card_name);
break;
}
if (val>2 && val<7) {
puts("the count has gone up!");
} else if(val>=10){
puts("The count has gone down");
}
return 0;
}
You're missing another break in the 'A' case. Your switch statement then should look something like this (I added indentation for you).
switch (card_name[0]) {
case 'K':
case 'Q':
case 'J':
val=10;
break;
case 'A':
val=11;
break; // you were missing a break statement here
default:
val=atoi(card_name);
break;
}
There is no break; for case 'A' .. Is that intentional ?
You are missing a break statement in case 'A':,before the default label. You should break after each statement in a case statement unless it was your intent to have the other cases execute, as well as a given case.
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Let's say I have code in C with approximately this structure:
switch (something)
{
case 0:
return "blah";
break;
case 1:
case 4:
return "foo";
break;
case 2:
case 3:
return "bar";
break;
default:
return "foobar";
break;
}
Now obviously, the breaks are not necessary for the code to run correctly, but it sort of looks like bad practice if I don't put them there to me.
What do you think? Is it fine to remove them? Or would you keep them for increased "correctness"?
Remove the break statements. They aren't needed and perhaps some compilers will issue "Unreachable code" warnings.
I would take a different tack entirely. Don't RETURN in the middle of the method/function. Instead, just put the return value in a local variable and send it at the end.
Personally, I find the following to be more readable:
String result = "";
switch (something) {
case 0:
result = "blah";
break;
case 1:
result = "foo";
break;
}
return result;
I would remove them. In my book, dead code like that should be considered errors because it makes you do a double-take and ask yourself "How would I ever execute that line?"
Remove them. It's idiomatic to return from case statements, and it's "unreachable code" noise otherwise.
Personally I would remove the returns and keep the breaks. I would use the switch statement to assign a value to a variable. Then return that variable after the switch statement.
Though this is an arguable point I've always felt that good design and encapsulation means one way in and one way out. It is much easier to guarantee the logic and you don't accidentally miss cleanup code based on the cyclomatic complexity of your function.
One exception: Returning early is okay if a bad parameter is detected at the beginning of a function--before any resources are acquired.
I'd normally write the code without them. IMO, dead code tends to indicate sloppiness and/or lack of understanding.
Of course, I'd also consider something like:
char const *rets[] = {"blah", "foo", "bar"};
return rets[something];
Edit: even with the edited post, this general idea can work fine:
char const *rets[] = { "blah", "foo", "bar", "bar", "foo"};
if ((unsigned)something < 5)
return rets[something]
return "foobar";
At some point, especially if the input values are sparse (e.g., 1, 100, 1000 and 10000), you want a sparse array instead. You can implement that as either a tree or a map reasonably well (though, of course, a switch still works in this case as well).
If you have "lookup" type of code, you could package the switch-case clause in a method by itself.
I have a few of these in a "hobby" system I'm developing for fun:
private int basePerCapitaIncomeRaw(int tl) {
switch (tl) {
case 0: return 7500;
case 1: return 7800;
case 2: return 8100;
case 3: return 8400;
case 4: return 9600;
case 5: return 13000;
case 6: return 19000;
case 7: return 25000;
case 8: return 31000;
case 9: return 43000;
case 10: return 67000;
case 11: return 97000;
default: return 130000;
}
}
(Yep. That's GURPS space...)
I agree with others that you should in most cases avoid more than one return in a method, and I do recognize that this one might have been better implemented as an array or something else. I just found switch-case-return to be a pretty easy match to a lookup table with a 1-1 correlation between input and output, like the above thing (role-playing games are full of them, I am sure they exist in other "businesses" as well) :D
On the other hand, if the case-clause is more complex, or something happens after the switch-statement, I wouldn't recommend using return in it, but rather set a variable in the switch, end it with a break, and return the value of the variable in the end.
(On the ... third? hand... you can always refactor a switch into its own method... I doubt it will have an effect on performance, and it wouldn't surprise me if modern compilers could even recognize it as something that could be inlined...)
Keep the breaks - you're less likely to run into trouble if/when you edit the code later if the breaks are already in place.
Having said that, it's considered by many (including me) to be bad practice to return from the middle of a function. Ideally a function should have one entry point and one exit point.
What do you think? Is it fine to remove them? Or would you keep them for increased "correctness"?
It is fine to remove them. Using return is exactly the scenario where break should not be used.
I would say remove them and define a default: branch.
Wouldn't it be better to have an array with
arr[0] = "blah"
arr[1] = "foo"
arr[2] = "bar"
and do return arr[something];?
If it's about the practice in general, you should keep the break statements in the switch. In the event that you don't need return statements in the future, it lessens the chance it will fall through to the next case.
For "correctness", single entry, single exit blocks are a good idea. At least they were when I did my computer science degree. So I would probably declare a variable, assign to it in the switch and return once at the end of the function
Interesting. The consensus from most of these answers seems to be that the redundant break statement is unnecessary clutter. On the other hand, I read the break statement in a switch as the 'closing' of a case. case blocks that don't end in a break tend to jump out at me as potential fall though bugs.
I know that that's not how it is when there's a return instead of a break, but that's how my eyes 'read' the case blocks in a switch, so I personally would prefer that each case be paired with a break. But many compilers do complain about the break after a return being superfluous/unreachable, and apparently I seem to be in the minority anyway.
So get rid of the break following a return.
NB: all of this is ignoring whether violating the single entry/exit rule is a good idea or not. As far as that goes, I have an opinion that unfortunately changes depending on the circumstances...
I say remove them. If your code is so unreadable that you need to stick breaks in there 'to be on the safe side', you should reconsider your coding style :)
Also I've always prefered not to mix breaks and returns in the switch statement, but rather stick with one of them.
I personally tend to lose the breaks. Possibly one source of this habit is from programming window procedures for Windows apps:
LRESULT WindowProc (HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
switch (uMsg)
{
case WM_SIZE:
return sizeHandler (...);
case WM_DESTROY:
return destroyHandler (...);
...
}
return DefWindowProc(hwnd, uMsg, wParam, lParam);
}
I personally find this approach a lot simpler, succinct and flexible than declaring a return variable set by each handler, then returning it at the end. Given this approach, the breaks are redundant and therefore should go - they serve no useful purpose (syntactically or IMO visually) and only bloat the code.
I think the *break*s are there for a purpose. It is to keep the 'ideology' of programming alive. If we are to just 'program' our code without logical coherence perhaps it would be readable to you now, but try tomorrow. Try explaining it to your boss. Try running it on Windows 3030.
Bleah, the idea is very simple:
Switch ( Algorithm )
{
case 1:
{
Call_911;
Jump;
}**break**;
case 2:
{
Call Samantha_28;
Forget;
}**break**;
case 3:
{
Call it_a_day;
}**break**;
Return thinkAboutIt?1:return 0;
void Samantha_28(int oBed)
{
LONG way_from_right;
SHORT Forget_is_my_job;
LONG JMP_is_for_assembly;
LONG assembly_I_work_for_cops;
BOOL allOfTheAbove;
int Elligence_says_anyways_thinkAboutIt_**break**_if_we_code_like_this_we_d_be_monkeys;
}
// Sometimes Programming is supposed to convey the meaning and the essence of the task at hand. It is // there to serve a purpose and to keep it alive. While you are not looking, your program is doing // its thing. Do you trust it?
// This is how you can...
// ----------
// **Break**; Please, take a **Break**;
/* Just a minor question though. How much coffee have you had while reading the above? I.T. Breaks the system sometimes */
Exit code at one point. That provides better readability to code. Adding return statements (Multiple exits) in between will make debugging difficult .
Simply define variable and return it at last of the switch statement and we can also remove default statement by setting variable= default value.
Ex:
switch(someVariable)
{
case 'a':
return a;
break;
case 'b':
return b;
break;
default:
return c;
}
solution:
$result = c; //for default value
switch(someVariable)
{
case 'a':
$result = a;
break;
case 'b':
$result = b;
break;
}
return $result; //simply return $result
This will lead to reduce your return statement.