Lesson 5.5. switch..case statement

In C, there is a conditional operator (switch..case) to compare a variable with several expressions.

Syntaxe

The general syntax is:

switch ( Variable ) {
    case Value1:  Instruction block 1;
                  break;

    case Value2:  Instruction block  2;
                  break;
    ...

    case ValueN:  Instruction block  N;
                  break;

    default:      Default instruction block;
}

• If Variable is equal to Value1, then instruction block 1 is executed.
• If Variable is equal to Value2, then instruction block 2 is executed.
• ...
• If Variable is equal to ValueN, then instruction block N is executed.
• If Variable is not equal to any of the valueX, the default block of instructions is executed.

Here is the associated flowchart:

Exemple

Here is an example that repeats a previous exercise. This time the sequence of if is replaced by a single switch..case :

// Display numbers in words
switch (number) {
    case 0: printf ("zero\n"); break;
    case 1: printf ("one\n"); break;
    case 2: printf ("two\n"); break;
    case 3: printf ("three\n"); break;
    case 4: printf ("four\n"); break;
    case 5: printf ("five\n"); break;
    case 6: printf ("six\n"); break;
    case 7: printf ("seven\n"); break;
    case 8: printf ("eight\n"); break;
    case 9: printf ("nine\n"); break;
    default : printf ("%d is not a number between 0 and 9\n", number);
}

Exercise

Exercise 1

Write a program that asks the user to enter a number. Using the switch..case statement display the number spelled out in French. This page list the spelling of French number.

unsigned int number;

// Asks the user to enter a number
printf ("Enter a number between 0 and 9 : ");
scanf ("%u", &number);

// Displays the number in full in French
// COMPLETE HERE

Here is the expected display:

Enter a number between 0 and 9 : 7
sept

Enter a number between 0 and 9 : 12
12 is not a number between 0 and 9.

#include <stdio.h> int main(void) { unsigned int number; // Asks the user to enter a number printf ("Enter a number between 0 and 9 : "); scanf ("%u", &number); // Displays the number in full in French // COMPLETE HERE return 0; }

Exercise 2

The variable number is now of type char and contains a character. If the character represents a number (from 0 to 9), the program displays this number in full in French. If it is not a number, we display : Non valid character.

char number = '7';

// Displays the number in full in French
// COMPLETE HERE

Here is the expected display with char number = '7';

sept

Here is the expected display with char number = 'x';

x is not a character between 0 and 9.

#include <stdio.h> int main(void) { char number = '7'; // Displays the number in full in French // COMPLETE HERE return 0; }

Exercise 3

Write a program that converts a hex character containing a hexadecimal symbol (from 0 to F). The result of the conversion in decimal will be assigned to the variable dec. We process only uppercase characters for the letters from A to F. If the character is not valid, we put -1 in the variable dec.

// Character to convert
char hex = 'B';
// Result in base 10
short dec;

// Convert hex to decimal (base 10)
// COMPLETE HERE

// Display the conversion result
if (dec==-1) printf ("Non valid hexadecimal number\n");
else printf ("0x%c = %d in decimal\n", hex, dec);

Here is the expected display with char hex = 'F';

0xF = 15 in decimal

Here is the expected display with char hex = 'f';

Non valid hexadecimal number

#include <stdio.h> int main(void) { // Character to convert char hex = 'B'; // Result in base 10 short dec; // Convert hex to decimal (base 10) // COMPLETE HERE // Display the conversion result if (dec==-1) printf ("Non valid hexadecimal number\n"); else printf ("0x%c = %d in decimal\n", hex, dec); return 0; }

Quiz

What does the following code display?

int x = 2;
switch (x) {
    case 0: printf ("Bonjour"); break;
    case 1: printf ("Hola"); break;
    case 2: printf ("Konnichiwa"); break;
    default : printf ("Hello");
}

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What does the following code display?

int x = 3;
switch (x) {
    case 0: printf ("Bonjour"); break;
    case 1: printf ("Hola"); break;
    case 2: printf ("Konnichiwa"); break;
    default : printf ("Hello");
}

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What syntax is used to test a range with a switch..case?

switch (grade) {
    //...
    ??? : printf ("Higest honors"); break;
    //...
}

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See also

• Learn C programming
• Lesson 1.1. History of C programming language
• Lesson 1.2. First program
• Lesson 1.3. Compilation
• Lesson 1.4. Preprocessor directives
• Lesson 1.5. Which compiler to choose?
• Lesson 1.6. Flowchart
• Lesson 2.1. Types and variables
• Lesson 2.2. Integers
• Lesson 2.3. Floating point numbers
• Lesson 2.4. Characters
• Lesson 2.5. Variables initialization
• Lesson 2.6. Ariane flight 501
• Lesson 3.1. Arithmetic operators
• Lesson 3.2. modulo
• Lesson 3.3. Operators and types
• Lesson 3.4. Type casting
• Lesson 3.5. Bitwise operators
• Lesson 3.6. Bitwise operators details
• Lesson 3.7. Shifting operators
• Lesson 3.8. Assignment operators
• Lesson 3.9. Increment and decrement operators
• Lesson 3.10. Comparison operators
• Lesson 3.11. Logical operators
• Lesson 3.12. Operator precedence
• Lesson 4.1. printf
• Lesson 4.2. scanf
• Lesson 4.3. putchar
• Lesson 5.1. Conditional branching (if...else)
• Lesson 5.2. Nested if and indentation
• Lesson 5.3. Checking intervals
• Lesson 5.4. Ternary Operator ?:
• Lesson 5.6. Break keyword in switch..case
• Lesson 6.1. do..while loop in C
• Lesson 6.2. While loop in C
• Lesson 6.3. For loop in C
• Lesson 6.4. How to choose the right loop in C ?
• Lesson 6.5. Exercices on loops in C
• Lesson 7.1. Bit masking
• Lesson 7.2. Bit masking, how to clear a bit in C?
• Lesson 7.3. Bit masking, how to set a bit in C?
• Lesson 7.4. Bit masking, how to toggle a bit in C?
• Lesson 7.5. Bit masking, how to check a single bit in C?
• Lesson 7.6. Overview of bit masking
• Lesson 8.1. Basic syntax of C functions
• Lesson 8.2. Calling C functions
• Lesson 8.3. Void keyword
• Lesson 8.4. Return keyword
• Lesson 8.5. Variable scope
• Lesson 8.6. Global variables
• Lesson 8.7. Static variables
• Lesson 8.8. Random numbers in C
• Lesson 8.9. Mathematical functions in C
• Lesson 9.1. Syntax of C arrays
• Lesson 9.2. Array initialization
• Lesson 9.3. Multidimensional arrays
• Lesson 9.4. How C arrays are stored in memory?
• Lesson 9.5. Arrays and functions
• Lesson 9.6. Exercises on C arrays
• Lesson 10.1. Strings in C
• Lesson 10.2. Null terminated string
• Lesson 10.3. The string.h library
• Lesson 10.4. String and functions
• Lesson 11.1. Introduction to pointers in C
• Lesson 11.2. Syntax of C pointers
• Lesson 11.3. Dynamic memory allocation
• Lesson 11.4. Incrementing pointers
• Lesson 11.5. Pointers as function argument in C
• Lesson 12.1. Introduction to structures in C
• Lesson 12.2. Properties of structures in C
• Lesson 12.3. Structures and pointers
• Lesson 12.4. Structures and functions
• Lesson 13.1. Recursive functions in C
• Lesson 13.2. Depth of recursive functions
• Lesson 13.2. Mutual recursion
• Lesson 14.1. Additional exercises

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