Why we are using ' : ' instead of ' ; ' in case control instruction?

Question

I need to know why we are using colon on keyword case in c programming and not semicolon?

/*valid statement*/
case 1:
   do this;
case 2:
   do this;

/*why is invalid to write */

case 1;
    do this;
case 2;
    do this;

help me please

Because `case`s are labels and thats the syntaxis for labels. — David Ranieri, Jun 03 '17 at 04:55
Early code was typeset using Gutenberg-style printing presses. Programmers kept running out of `;` symbols, so they decided to switch to `:` for case statements so they could write longer programs. — BJ Myers, Jun 03 '17 at 05:35
@BJMyers not sure. I heard that it was just a typo by Ritchie when documenting the language. — ThingyWotsit, Jun 03 '17 at 06:00
Why is this labeled C#? C and C# aren't even remotely the same language. — EJoshuaS - Stand with Ukraine, Jun 03 '17 at 06:15

Harrison Smith · Accepted Answer · 2021-01-18T01:01:00.410

Why a case line shouldn't be ended with a semicolon

In C-based languages, the semicolon has a specific function as the 'statement terminator'. This means that a semicolon marks the end of a specific statement of code, and the start of another. For more info on this see this quora post.

Therefore if you had a semicolon after each case line, the compiler would interpret them all as separate, individual statements. It would be like writing:

do case 1;
do this;
do case 2;
do this;

The compiler sees these as individual, 'normal' lines of code. It will probably then fail to compile, because the case keyword is specifically reserved only for use within switch statements.

As to why the : character was selected for this particular purpose: as Luca_65 mentioned the case is hiding a goto label statement. The colon is used in C to label a section of code, and this syntax has followed through to it's derivative languages.

As Bobby Speirs noted, that character was probably originally chosen due to the colon's similar meaning in English grammar.

score 0 · Answer 2 · answered Jun 03 '17 at 05:02

0

The colon makes more sense from an English writing point of view, which makes the code easier to read.

Think of it like telling the computer the following:

In case the number is 1, you should do these things: 
    Thing 1;
    Thing 2;
    Thing 3;

answered Jun 03 '17 at 05:02

Bobby Speirs

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score 0 · Answer 3 · answered Jun 03 '17 at 05:31

0

C switch hide a goto to the label equal to the value under test.

answered Jun 03 '17 at 05:31

Luca_65

123
9

score 0 · Answer 4 · answered Jun 03 '17 at 05:37

Quoting C11, chapter §6.8.1

A case or default label shall appear only in a switch statement.

So, a case is a labeled-statement.

the prescribed format of a labeled statement is given by

labeled-statement:
identifier : statement
case constant-expression : statement
default : statement

Regarding the choice of the :, this is in regards to the assembly syntax, where : is used to identify a designated block of statement.

Why we are using ' : ' instead of ' ; ' in case control instruction?

4 Answers4