Switch Statement in Computer Programming, C Language

There is another important branching statement known as the switch statement in computer programming. We know that (discussed earlier), in situations involving series of decisions one after the other, the if-else-if ladder can be used. Each and every condition may involve expressions which results in various data types such as float, double, char, integer etc.

Here, if-else-if ladder or nested if can be used. But, in situations involving series of decisions one after the other, each decision condition may involve expressions which result in integer value. This integer value may be used for comparison using equality operator "==". In these situations, where the result is of integer data type and series of integer values are used in equality decisions, the usage of switch statement is recommended, because it improves readability of the program.

The switch statement provides a way to select a choice out of several choices based on the selection of choice. The choice can either be an integer value or a character value. The choice can also be an expression which results in an integer value. Based on this integer value, the control is transferred to a particular case value.

The syntax of the switch statement is as follows:
switch (expression/choice)
{
  case value1:
      statement(s);
    break;
case value2:
    statement(s);
    break;
case value3:
    statement(s);
    break;
    .
    .
    .
default:
    statement(s);
}
The expression or choice in switch statement is evaluated to an integer value. The integer value thus obtained if matches with any of the values value1, value2, value3……, value n, then the control is transferred to the appropriate case statement(s). During execution of a particular case, if break is not encountered, then control goes to the subsequent case and the statement(s) under that case will be executed till the break statement is encountered.
If the value of the expression does not match with any of the cases values value1, value2,… value n then, control comes out of the switch statement in the absence of default. If default case is part of the switch then the statement(s) in default block will be executed.

Here, we are writing a program to simulate the calculator using switch statement. The input is an expression of the form P op Q Where P and Q are the operands and the op is an operator. For example, a + b, 10 * 20 etc. Based on the operator, the operations is performed and the result is displayed.

Algorithm:
Step1:    Read p, op, q;
Step2:    switch(op)
    case ‘+’:    result = p + q;
    case ‘-’:    result = p - q;
    case ‘*’:    result = p * q;
    case ‘/’:    result = p / q;
    default:    Write: ‘Invalid operator’
    [End of switch]
Step3:    Write: result
Step4:    Exit
   
C program of the above problem in C language:
main()
{
int p,q,result;
char op;
clrscr();
printf(“Enter an expression here:\n”);
scanf(“%d %c %d”,&p,&op,&q);
switch(op)
{
 case ‘+’:
 result = p + q;
break;
case ‘-’:
 result = p - q;
break;
case ‘*’:
 result = p * q;
break;
case ‘/’:
 result = p / q;
break;
default:
printf(“Invalid expression.\n”);
}
printf(“The result of the expression %d %c %d = %d”,p,op,q,result);
getch();
}

Advantages:

• Improves readability of the program
• More structure way of writing  the program

Disadvantage:

It can be used only if the expression used for checking the conditions result in integer value or character value. If the result of expression is not integer value, switch statement cannot be used.


If-Else-If Ladder
For loop in C