From 754bbf7a25a8dda49b5d08ef0d0443bbf5af0e36 Mon Sep 17 00:00:00 2001 From: Craig Jennings Date: Sun, 7 Apr 2024 13:41:34 -0500 Subject: new repository --- devdocs/c/language%2Fswitch.html | 88 ++++++++++++++++++++++++++++++++++++++++ 1 file changed, 88 insertions(+) create mode 100644 devdocs/c/language%2Fswitch.html (limited to 'devdocs/c/language%2Fswitch.html') diff --git a/devdocs/c/language%2Fswitch.html b/devdocs/c/language%2Fswitch.html new file mode 100644 index 00000000..83c773e6 --- /dev/null +++ b/devdocs/c/language%2Fswitch.html @@ -0,0 +1,88 @@ +

switch statement

Executes code according to the value of an integral argument.

+

Used where one or several out of many branches of code need to be executed according to an integral value.

+

Syntax

+ +
attr-spec-seq(optional) switch ( expression ) statement
+ + + +
attr-spec-seq - (C23)optional list of attributes, applied to the switch statement
expression - any expression of integer type (char, signed or unsigned integer, or enumeration)
statement - any statement (typically a compound statement). case: and default: labels are permitted in statement, and break; statement has special meaning.
+ + + + +
case constant-expression : statement (1) (until C23)
attr-spec-seq(optional) case constant-expression : statement(optional) (1) (since C23)
default : statement (2) (until C23)
attr-spec-seq(optional) default : statement(optional) (2) (since C23)
+ + +
constant-expression - any integer constant expression
attr-spec-seq - (C23)optional list of attributes, applied to the label

Explanation

The body of a switch statement may have an arbitrary number of case: labels, as long as the values of all constant-expressions are unique (after conversion to the promoted type of expression). At most one default: label may be present (although nested switch statements may use their own default: labels or have case: labels whose constants are identical to the ones used in the enclosing switch).

+

If expression evaluates to the value that is equal to the value of one of constant-expressions after conversion to the promoted type of expression, then control is transferred to the statement that is labeled with that constant-expression.

+

If expression evaluates to a value that doesn't match any of the case: labels, and the default: label is present, control is transferred to the statement labeled with the default: label.

+

If expression evaluates to a value that doesn't match any of the case: labels, and the default: label is not present, none of the switch body is executed.

+

The break statement, when encountered anywhere in statement, exits the switch statement:

+
switch(1) {
+    case 1 : puts("1"); // prints "1",
+    case 2 : puts("2"); // then prints "2" ("fall-through")
+}
switch(1) {
+    case 1 : puts("1"); // prints "1"
+             break;     // and exits the switch
+    case 2 : puts("2");
+             break;
+}
+ +

As with all other selection and iteration statements, the switch statement establishes block scope: any identifier introduced in the expression goes out of scope after the statement.

+

If a VLA or another identifier with variably-modified type has a case: or a default: label within its scope, the entire switch statement must be in its scope (in other words, a VLA must be declared either before the entire switch or after the last label):

+
switch (expr)
+{
+        int i = 4; // not a VLA; OK to declare here
+        f(i); // never called
+//      int a[i]; // error: VLA cannot be declared here
+    case 0:
+        i = 17;
+    default:
+        int a[i]; // OK to declare VLA here
+        printf("%d\n", i); // prints 17 if expr == 0, prints indeterminate value otherwise
+}
 (since C99)

Keywords

switch, case, default

+

Example

#include <stdio.h>
+ 
+void func(int x)
+{
+   printf("func(%d): ", x);
+   switch(x)
+   {
+      case 1: printf("case 1, ");
+      case 2: printf("case 2, ");
+      case 3: printf("case 3.\n"); break;
+      case 4: printf("case 4, ");
+      case 5:
+      case 6: printf("case 5 or case 6, ");
+      default: printf("default.\n");
+   }
+}
+ 
+int main(void)
+{
+   for(int i = 1; i < 9; ++i) func(i);
+}

Output:

+
func(1): case 1, case 2, case 3.
+func(2): case 2, case 3.
+func(3): case 3.
+func(4): case 4, case 5 or case 6, default.
+func(5): case 5 or case 6, default.
+func(6): case 5 or case 6, default.
+func(7): default.
+func(8): default.

References

See also

+
C++ documentation for switch statement
+

+ © cppreference.com
Licensed under the Creative Commons Attribution-ShareAlike Unported License v3.0.
+ https://en.cppreference.com/w/c/language/switch +

+
-- cgit v1.2.3