The switch statement in C provides a way to execute different parts of code based on the value of an expression. It enhances code readability and efficiency, especially when dealing with multiple conditions.
The switch statement evaluates an expression and executes the corresponding case block that matches the expression’s value.
switch (expression) {
case constant1:
// code to execute if expression == constant1
break;
case constant2:
// code to execute if expression == constant2
break;
// more cases...
default:
// code to execute if no case matches
}Example
#include <stdio.h>
int main() {
int day = 3;
switch (day) {
case 1:
printf("Monday\n");
break;
case 2:
printf("Tuesday\n");
break;
case 3:
printf("Wednesday\n");
break;
case 4:
printf("Thursday\n");
break;
case 5:
printf("Friday\n");
break;
case 6:
printf("Saturday\n");
break;
case 7:
printf("Sunday\n");
break;
default:
printf("Invalid day\n");
}
return 0;
}The switch statement evaluates the expression once and compares it with each case. If a match is found, the corresponding block of code is executed until a break statement is encountered or the switch ends.
Role of the break statement
The break statement terminates the switch block, preventing the execution from falling through to subsequent cases.
switch (value) {
case 1:
// code
break;
case 2:
// code
break;
default:
// code
}The default case is optional and is executed if none of the specified case values match the expression. It acts as a fallback mechanism.
Example with the default statement:
#include <stdio.h>
int main() {
char grade;
// Prompt user for input
printf("Enter your grade (A, B, C, D, F): ");
fflush(stdout);
scanf(" %c", &grade); // Note the space before %c to consume any leftover whitespace
// Using switch statement to evaluate the grade
switch (grade) {
case 'A':
case 'a':
printf("Excellent!\n");
break;
case 'B':
case 'b':
case 'C':
case 'c':
printf("Well done\n");
break;
case 'D':
case 'd':
printf("You passed\n");
break;
case 'F':
case 'f':
printf("Better try again\n");
break;
default:
printf("Invalid grade\n");
}
return 0;
}Multiple case labels can share the same block of code, allowing for cleaner and more efficient code when different values require the same action.
#include <stdio.h>
#include <ctype.h> // For tolower function
int main() {
char ch;
// Prompt the user for an input
printf("Enter a single alphabet character: ");
fflush(stdout);
scanf(" %c", &ch); // The space before %c ignores any leading whitespace
// Convert the character to lowercase to handle both cases
ch = tolower(ch);
// Using switch statement to check for vowels
switch (ch) {
case 'a':
case 'e':
case 'i':
case 'o':
case 'u':
printf("Vowel\n");
break;
default:
// Check if the character is an alphabet
if ((ch >= 'a' && ch <= 'z')) {
printf("Consonant\n");
} else {
printf("Invalid input. Please enter an alphabet character.\n");
}
}
return 0;
}Missing break statements
Forgetting to include break can cause unintended fall-through, leading to multiple cases being executed.
#include <stdio.h>
int main() {
int value;
// Prompt user for input
printf("Enter a number (1-2): ");
fflush(stdout);
scanf("%d", &value);
// Using switch statement
printf("\nUsing switch:\n");
switch (value) {
case 1:
printf("One\n");
// Intentional fall-through: no break here
case 2:
printf("Two\n");
break;
default:
printf("Other\n");
}
return 0;
}
Output when value is 1:
One
Two
Non-integral types
The switch statement only works with integral types (e.g., int, char). Using non-integral types like float or double will result in a compilation error.
break: prevents accidental fall-through by terminating each case with a break statement.case: handles unexpected values and enhances code robustness.case should handle a single responsibility to maintain readability.Use switch when you have multiple discrete values to compare against a single expression. It is often more readable and efficient than multiple if-else statements in such scenarios.
Example comparison:
Using if-else:
#include <stdio.h>
int main() {
int day;
// Prompt user for input
printf("Enter day number (1-3): ");
fflush(stdout);
scanf("%d", &day);
// Using if-else
printf("\nUsing if-else:\n");
if (day == 1) {
printf("Monday\n");
} else if (day == 2) {
printf("Tuesday\n");
} else if (day == 3) {
printf("Wednesday\n");
} else {
printf("Invalid day\n");
}
return 0;
}
Using switch:
#include <stdio.h>
int main() {
int day;
// Prompt user for input
printf("Enter day number (1-3): ");
fflush(stdout);
scanf("%d", &day);
// Using switch
printf("\nUsing switch:\n");
switch (day) {
case 1:
printf("Monday\n");
break;
case 2:
printf("Tuesday\n");
break;
case 3:
printf("Wednesday\n");
break;
default:
printf("Invalid day\n");
}
return 0;
}
What is a fall-through behavior?
Fall-through behavior in C’s switch statements occurs when, after executing a matching case block, the program continues to execute subsequent case blocks without encountering a break statement.
This means that once a case is matched, all code following it runs sequentially until a break, return, or the end of the switch is reached.
Intentional fall-through can be used when multiple cases share common code. However, it should be used sparingly and documented clearly to avoid confusion.
#include <stdio.h>
int main() {
int level;
// Prompt user for input
printf("Enter level number (1-2): ");
fflush(stdout);
scanf("%d", &level);
// Using switch statement to evaluate the level
switch (level) {
case 1:
printf("Level 1\n");
// Intentional fall-through: no break here
case 2:
printf("Level 2\n");
break;
default:
printf("Unknown level\n");
}
return 0;
}Example output
If level is 1:
Level 1
Level 2
If level is 2:
Level 2
