In C programming, the "switch" statement is used to perform different actions based on the value of a single expression. The syntax for a "switch" statement is as follows:

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switch (expression) {    case value1:        // code to be executed if expression == value1        break;    case value2:        // code to be executed if expression == value2        break;    ...    default:        // code to be executed if expression does not match any of the values }

The "expression" is the value that is being tested, and "value1", "value2", etc. are the different possible values that the expression can take. Each case is followed by a colon and the code to be executed if the expression matches that case's value. The break statement is used to exit the switch statement and continue with the next statement after the switch.

Here is an example of a program that uses a switch statement to determine the day of the week based on a number:

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#include <stdio.h> int main() {    int day;    printf("Enter a number (1-7): ");    scanf("%d", &day);    switch (day) {        case 1:            printf("Monday");            break;        case 2:            printf("Tuesday");            break;        case 3:            printf("Wednesday");            break;        case 4:            printf("Thursday");            break;        case 5:            printf("Friday");            break;        case 6:            printf("Saturday");            break;        case 7:            printf("Sunday");            break;        default:            printf("Invalid input");    }    return 0; }

In this example, the program prompts the user to enter a number between 1 and 7. The switch statement then checks the value of the "day" variable against the different case values. If the value of "day" matches the value of a case, the code associated with that case is executed and the break statement is encountered, which exits the switch statement. If the value of "day" does not match any of the case values, the code associated with the default case is executed.

The switch statement is more efficient than a series of if-else statements when testing a single variable against many possible values because it directly compares the variable with the case values rather than using a series of relational operators.