What is Switch Case Statement?

Answer 1

The switch statement immediately passes control to a case label within its body, dependant upon the evaluation of an expression. This allows us to control complex conditional and branching operations.

Each case label contains a constant expression, which must match one of the possible evaluations of the switch expression. No two case labels may hold the same constant. An optional "catch-all" label, the default label, may also be included but it must follow all other case labels.

When control passes to a case label, execution continues from that point on until the end of the switch body unless a break statement is encountered before the end of the switch body. A break statement forces execution to pass to the statement immediately following the switch body. Return and goto statements can be used in place of a break statement where required. Switch statements can also be nested if required.

Although some switch statements can be implemented as a series of if..else if.. statements, switch statements are more efficient as there's only one evaluation required rather than a separate evaluation for each if statement. Moreover, case labels allow greater control over the flow of execution.

As a simple example, suppose we wish to count the number of characters in a string along with the number of times a specific letter is used including how many of them are capitals. One way of doing this is to traverse the string and increment counters using a switch statement:

char str[]="This is a test string";

int chars=0, ts=0, capts=0;

for( int i = 0; i<sizeof(str); ++i )

{

switch( str[i] )

{

case( 'T' ): ++capts;

case( 't' ): ++ts;

default: ++chars;

}

}

printf( "String: "%s"\n", str );

printf( "The string has %d character%s in total\n", chars, chars>1?"s":"" );

printf( "There %s %d letter 't'%s in total\n", ts>1?"are":"is", ts, ts>1?"s":"" );

printf( "There %s %d capital 't'%s in total\n", capts>1?"are":"is", capts, capts>1?"s":"" );

Output:

String: "This is a test string"

The string has 22 characters in total

There are 4 letter 't's in total

There is 1 capital 't' in total

If we wanted separate counts of upper and lower case letters, then we can simply change the switch statement to suit:

switch( str[i] )

{

case( 'T' ): ++capts; break;

case( 't' ): ++ts;

}

++chars;

If were to reproduce the original switch statement using if..else if.. we'd need to use the following instead:

if( str[i] 't' )

++ts;

++chars;

Although this looks fine, we are forced to evaluate str[i] twice if it is not equal to 'T'. In the switch statement, we only need to evaluate str[i] once. If..else if.. should only be used when evaluating completely different expressions. If you're evaluating the same value or need more control over the execution path, then switch is much more efficient.

Note that in complex switch statements, the order of the case labels is important if execution is allowed to flow from once case label to the next. Case labels only indicate where execution will begin. After that they are ignored (just as goto labels are ignored). You must use break, return or goto statements to control where execution ends, otherwise execution will continue through all the following cases. Sometimes that is desirable (as shown in the example above), but often it is not. In most cases, the last statement of a case will be break statement.

Answer 2

The switch statement takes a variable, and then has 'cases' which are executed depending on the value of the variable. For example, take this code snippet:

switch (x)
{
case 1:
cout << "X is One";
break;
case 2:
cout << "X is Two";
break;
case 7:
cout << "X is Seven";
break;
default:
cout << "X isn't one, two, or seven";
break;
}


As you can see, after each 'case', you need a break to keep from executing the other cases after it. At the very end is an optional 'default' which executes if none of the others did. One big difference from if-else-if ladders is that case statements cannot test for logical or inequality (like < , >, or, and and), but only equality ( == ).


You can also use a case statement with a char variable, but you must surround the case designator with single quotes.


case 'h': cout << "the character is h";
break;


Like that. Happy programming!

Answer 3

Switch statement is used in C Programming language when we wish to use multiple decision statement. The difference between decision control structure and switch case is that in decision control structure we can use only 2 decision or condition but in switch case we can use multiple decision statements....

for Ex--

#include<stdio.h>

#include<conio.h>

void main()

{

int a;

printf("Enter the value");

scanf("%d",&a);

if(a>5)

printf("Good");

else

printf("bad");

getch();

}

switch case--

#include<stdio.h>

#include<conio.h>

void main()

{

int i=22;

switch(i)

{

case 121:

printf("abc");

break;

case 22:

printf("def");

break ;

case 457:

printf("gfde");

break;

case1:

printf("007");

break;

default:

printf("I m in default");

}

}

We can see that we can give as many choices we want in switch case which is not possible in decision control statement.

Answer 4

The switch statement immediately passes control to a case label within its body, dependant upon the evaluation of an expression. This allows us to control complex conditional and branching operations.

Each case label contains a constant expression, which must match one of the possible evaluations of the switch expression. No two case labels may hold the same constant. An optional "catch-all" label, the default label, may also be included but it must follow all other case labels.

When control passes to a case label, execution continues from that point on until the end of the switch body unless a break statement is encountered before the end of the switch body. A break statement forces execution to pass to the statement immediately following the switch body. Return and goto statements can be used in place of a break statement where required. Switch statements can also be nested if required.

Although some switch statements can be implemented as a series of if..else if.. statements, switch statements are more efficient as there's only one evaluation required rather than a separate evaluation for each if statement. Moreover, case labels allow greater control over the flow of execution.

As a simple example, suppose we wish to count the number of characters in a string along with the number of times a specific letter is used including how many of them are capitals. One way of doing this is to traverse the string and increment counters using a switch statement:

char str[]="This is a test string";

int chars=0, ts=0, capts=0;

for( int i = 0; i<sizeof(str); ++i )

{

switch( str[i] )

{

case( 'T' ): ++capts;

case( 't' ): ++ts;

default: ++chars;

}

}

printf( "String: "%s"\n", str );

printf( "The string has %d character%s in total\n", chars, chars>1?"s":"" );

printf( "There %s %d letter 't'%s in total\n", ts>1?"are":"is", ts, ts>1?"s":"" );

printf( "There %s %d capital 't'%s in total\n", capts>1?"are":"is", capts, capts>1?"s":"" );

Output:

String: "This is a test string"

The string has 22 characters in total

There are 4 letter 't's in total

There is 1 capital 't' in total

If we wanted separate counts of upper and lower case letters, then we can simply change the switch statement to suit:

switch( str[i] )

{

case( 'T' ): ++capts; break;

case( 't' ): ++ts;

}

++chars;

If were to reproduce the original switch statement using if..else if.. we'd need to use the following instead:

if( str[i] 't' )

++ts;

++chars;

Although this looks fine, we are forced to evaluate str[i] twice if it is not equal to 'T'. In the switch statement, we only need to evaluate str[i] once. If..else if.. should only be used when evaluating completely different expressions. If you're evaluating the same value or need more control over the execution path, then switch is much more efficient.

Note that in complex switch statements, the order of the case labels is important if execution is allowed to flow from once case label to the next. Case labels only indicate where execution will begin. After that they are ignored (just as goto labels are ignored). You must use break, return or goto statements to control where execution ends, otherwise execution will continue through all the following cases. Sometimes that is desirable (as shown in the example above), but often it is not. In most cases, the last statement of a case will be break statement.