switch-statements.md

Switch statements

Similar to an If statements except there is no condition to test for. We can provide a variable number and when the value of number matches the case the code for that case is executed.

In the example below, integer variable number is assigned 0. When the switch statement case matches number the printf statement is executed.

#include <stdio.h>

int main(void)
{

    int number = 0;

    switch (number) 
    {
        case 0:
            printf("Case 0!\n");
        case 1:
            printf("Case 1!\n");
    }

    return 0;
}

Output:

Case 0!
Case 1!

Once the first matching case is found then subsequent case statements are also executed. This is known as fall through logic. We can prevent this using break; statement as shown.

#include <stdio.h>

int main(void)
{

    int number = 0;

    switch (number) 
    {
        case 0:
            printf("Case 0!\n");
            break;
        case 1:
            printf("Case 1!\n");
            break;
    }

    return 0;
}

Using the break statement will exit the switch statement.

Output:

Case 0!

We can define a default case. This case will always execute if none of the other cases match.

#include <stdio.h>

int main(void)
{

    int number = 2;

    switch (number) 
    {
        case 0:
            printf("Case 0!\n");
            break;
        case 1:
            printf("Case 1!\n");
            break;
        default:
            printf("Default case!\n");
    }

    return 0;
}

Output:

Default case!

As the default is last is doesn't need a break.

Using fall through logic

As seen once the first match has been found the subsequent case statement are executed.

Here is a program which will count the number of a letters and the number of vowels in a string.

#include <stdio.h>
#include <ctype.h>
#include <string.h>

int main(void)
{
    char s[] = "aeioxyz";

    int length = strlen(s);

    int a = 0;
    int vowel = 0;

    for (int i = 0; i < length; i++)
    {
        switch (toupper(s[i])) 
        {
            case 'A':
                a++;
            case 'E':
            case 'I':
            case 'O':
            case 'U':
                vowel++;
        }
    }

    printf("a: %d, vowels: %d\n", a, vowel);
}

Output

a: 1, vowels: 4

No break statements are used, the vowel counter is incremented when s[i] contains a vowel.

Some programmers favour If statements as they are easily to understand and can provide the same functionality.