Switch Case Structures in C: Multiple Selection with Examples, Slides of Computer Engineering and Programming

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Switch Case Structures

Lecture 9

Switch Multiple Selection Structure

• A multiple selection structure is useful when an algorithm contains a series of decisions in which a variable or expression is tested separately for one of several possible integral values.
• Each integral value represents a different action to be taken in the algorithm.
• C provides the switch multiple selection structure to implement this type of decision making.

Switch-Case Structures

• The switch is the "controlling expression"
  • Can only be used with constant integer expressions.
  • Remember, a single character is a small positive integer.
  • The expression appears in ( )
• The case is a "label"
  • The label must be followed by a " : "
  • Braces, { }, not required around statements

Switch-Case Structures

• Unlike if-else if-else structures, when the value in a case matches the test value, all of the actions in the rest of the structure take place.
• This is shown in the following program where the user enters a value that matches the first case and every action in the structure is executed.

A Sample Program to Illustrate Switch-

Case

Algorithm:

1. Set up the environment
2. Prompt user to enter his/her letter grade
3. Get user’s response
4. If grade is a or A say “Good Job” and go to 9
5. If grade is b or B say “Pretty good” and go to 9
6. If grade is c or C say “Better get to work” and go to 9 7 If grade is d or D say “You are in trouble” and go to 9
7. Say “You are failing”
8. Terminate program

A Sample Program to Illustrate Switch-

Case

/* This program associates a letter grade with a message appropriate to the score. */

#include <stdio.h>

int main ( ) { char grade ; printf ("Enter your current letter grade\n") ; grade = getchar ( ) ;

A Sample Program to Illustrate Switch-

Case

case ('c') : case ('C') : printf ("Better get to work.\n") ; case ('d') : case ('D') : printf ("You are in trouble.\n") ; default : printf ("You are failing!!\n") ; } /* End of switch-case structure / } / End of main program */

Switch-Case Structures

Resultant Output from Grade

Program

/* The following results are produced when the user enters an "A" as input to the program prompt. */

Good Job!

Pretty good.

Better get to work. Docsity.com

Fixed Program using Switch-Case

#include <stdio.h> Structures

int main ( ) { int grade ; printf ("Enter your current letter grade\n") ; while ( ( grade = getchar ( ) ) != EOF) { switch (grade) { case ('a') : case ('A') : printf ("Good Job!\n") ; break ;

Fixed Program using Switch-Case

Structures

case ('b') : case ('B') : printf ("Pretty good.\n") ; break ; case ('c') : case ('C') : printf ("Better get to work.\n") ; break ; case ('d') : case ('D') : printf ("You are in trouble.\n") ; break ; Docsity.com

Comments on Last Example

Program

• Use of the while repetition structure -- more discussion on repetition structures later this week.
• Use of the end-of-file, or EOF, test. Note that EOF (a DEFINED constant) is a negative integral value, usually a -1 on most (but not all) systems. (EOF is actually defined in the <stdio.h> header file.)
• Use of ints (instead of chars). Why?
• From the keyboard, a <cntrl-d> Docsity.com

Comments on Last Example

Program

• The statements: case (' ') : case ('\n') : break ; were used to clear the keyboard input buffer.
• Another way to clear it is with the statement: fgets(input_flush,256,stdin); where fgets(char_strg, len_char_strg, file_pointer);
• This fgets statement can prove very useful in today’s daily assignment.
• The two sample programs which follow show why flushing the input stream is important

Output from Flawed Sample Program

input a char followed by e

ans2 = >> e <<

input a char followed by ans2 = >>

In this case a newline character which is produced by the^ << or is read by getchar on the second time through the loop

Correct Sample Input Program

• #include <stdio.h>
• Int main()
• {
• char ans2,input_flush[256];
• while(ans2 != ‘E’)
• {
• printf(“\n Input a character followed by ”);
• ans2 = getchar();
• fgets(input_flush,256,stdin); // Input buffer is flushed
• // The is not in buffer
• printf(“ ans2 >> %c <<\n”,ans2);
• }
• }