Handling Multiple Choices

    In many occasions we come across situations where we are required to choose one thing out of many. This can be handled by using nested if - else if - else if ... else structure.

C also provides a special control structure that allows us to handle such cases effectively, rather than using a series of if statements.

Case Control Structure

The control structure in C, which allows as to make a selection out of a number of choices is called a switch. It consists of three keywords switch - case - default.

Syntax : switch (<expression>) <statement>
                         case <constant expression>
                         default;


switch <expression>
{
case <constant expression>:
               do this;
case <constant expression>:
               do this;
default :
               do this;
}


switch Causes control to branch to one of a list of possible statements in the block defined by <statement>
           
case The list of possible branch points within <statement> is determined by preceding sub statements with     case <constant expression>; where <constant expression> must be an int and must be unique.

Once a value is computed for <expression>, the list of possible <constant expression> values determined from all case statements is searched for a match. If a match is found, execution continuous until a break statementis encountered or the end of <statement> is reached.

default If a switch is not found and "default : " statement prefix is found within <statement>, execution     continues at this point. Otherwise<statement> is skipped entirely.

The loop control structure

The programs so far we have discussed followed either a sequential or a decision control structure. In the sequential structure the execution of statements was carried out in a fixed order while in the selection structure the execution of statements was carried out depending on the outcome of a condition being over, with variations in the details each time. The structure that meets this need is the Repetitive Control Structure and its action is termed 'looping'.

Repetition

The versatility of a computer lies in its ability to perform a set of instructions repeatedly. This involves repeating some parts of a program, a specified number of times or until a particular condition is full-filled. This is achieved by using the 'Repititive' or loop control structure.

/* Day of week */
#include <stdio.h>
#include <conio.h>
int main()
{
            int day;
            printf(“Enter day of the week : ”);
            scanf(“%d”, &day);
            switch (day)
                 {
                        case 1:
                                printf(“Today is Sunday \n”);
                                break;
                        case 2:
                                printf(“Today is Monday \n”);
                                break;
                        case 3:
                                printf(“Today is Tuesday \n”);
                                break;
                        case 4:
                                printf(“Today is Wednesday \n”);
                                break;
                        case 5:
                                printf(“Today is Thursday \n”);
                                break;
                        case 6:
                                printf(“Today is Friday \n”);
                                break;
                        case 7:
                                printf(“Today is Saturday \n”);
                                break;
                        default :
                                printf(“Wrong entry! \n”);
                 }
}