Lesson 2.2. Integers

Integer type

The integer type is to store integers. There are 4 types used to encode integers in C. Depending on the size of the values to be stored, you have to choose the appropriate type :

Type	Bytes	Bits	Minimum	Maximum
char	1	8	-128	+127
short int	2	16	-32 768	+32 767
int	4	32	-2 147 483 648	+2 147 483 647
long int	8	64	-9 223 372 036 854 775 808	+9 223 372 036 854 775 807

For types short int and long int, there is a short writing: short and long :

short Var;
long Var = 2;

It is important to choose the best type for each variable to save memory. For example, if you use a long to store a number between 1 and 10, you will occupy 4 bytes when only one would be enough.

Depending on the compiler and/or the target, the size of the types may vary. For example, if we compiled for an Arduino, an integer will be stored on 2 bytes. It is possible to know the size of a type with the sizeof() function. We will see an example below.

Unsigned

When types are preceded by the keyword unsigned, this specifies that the variable will be un-signed. In other words, it will not have a sign (+ or -). The value contained in the variable is necessarily positive:

Type	Bytes	Bits	Minimum	Maximum
unsigned char	1	8	0	255
unsigned short int	2	16	0	65535
unsigned int	4	32	0	4294967295
unsigned long int	8	64	0	+18 446 744 073 709 551 615

Initialization

Integers can obviously be initialized with a value expressed in decimal base:

int x = 12;

It is also possible to initialize integers with a hexadecimal value using the 0x syntax:

// The integer x is initialized with the hexadecimal value C ( 0x0C = 12 in base 10)
int x = 0xC;

On the notation of hexadecimal values, C is not case sensitive (upper or lower case are allowed):

int var = 0xA12F;

is identical to:

int var = 0xa12f;

In standard C, it is not possible to initialize a variable directly in base 2. However, some compilers accept the 0b notation, generally compilers dedicated to to embedded systems.

// This line does not meet the standards of C
// and is not supported by many compilers
PORTA = 0b10110110;

To ensure code compatibility, it is best to avoid this notation. The best solution is to initialize in hexadecimal with an appropriate comment as in this example:

//  |  b7 |  b6 |  b5 |  b4 |  b3 |  b2 |  b1 |  b0 |
//  |  1  |  0  |  1  |  1  |  0  |  1  |  1  |  0  | 
PORTA = 0xB6;

Display

When displaying a variable with the printf function, you have to use a format code. This is a special sequence of characters which tells the function that this sequence must be replaced by the value of the variable.

For example, to display the N integer variable , we use the %d format code:

int N=12;
printf ("%d", N);

The following table presents the format codec for each type:

Type	Format code
char	%d
unsigned char	%d ou %u
short	%i
unsigned short	%u
int	%d ou %i
unsigned int	%u
long	%ld ou %li
unsigned long	%lu

Here is an example that display a long int (10e10 = \( 10^{10} \) ) :

unsigned long N=10e10;
printf ("%lu", N);

Exercises

Exercise 1

The code below displays the size of a char and a short. To retrieve the size of a type, we use the sizeof() instruction which returns its size in bytes. Note that sizeof() returns a value comparable to an unsigned long int, which explains the format code %lu in the printf. Complete the code so that the program also displays the size of an int and a long.

#include <stdio.h>

int main(void) {

    // Size in bytes :
    printf("Size of a char = %lu bytes\n", sizeof(char));
    printf("Size of a short = %lu bytes\n", sizeof(short));

    // COMPLETE HERE

    return 0;
}

#include <stdio.h> int main(void) { // Size in bytes : printf("Size of a char = %lu bytes\n", sizeof(char)); printf("Size of a short = %lu bytes\n", sizeof(short)); // COMPLETE HERE return 0; }

Exercise 2

The code below displays the size of a char in bits. Complete the code below so that it also displays the size of an int and a long.

#include <stdio.h>

int main(void) {
    // Size in bits:
    printf("Size of a char = %lu bits\n", sizeof(char)*8 );

    // COMPLETE HERE

    return 0;
}

#include <stdio.h> int main(void) { // Size in bits: printf("Size of a char = %lu bits\n", sizeof(char) * 8); // COMPLETE HERE return 0; }

Exercise 3

The code below is provided:

#include <stdio.h>

int main(void) {

  // Declaration and assignment of the variable a 
  char a=100;  

  // Add 1 to the variable a
  a = a + 1;

  // Display the final value of a
  printf("100 + 1  = %d", a);    

  return 0;
}

1. Analyse and run the code
2. Replace the first line with char a=127;.
3. Run the program, what happens?
4. Change the type of a to solve the issue

#include <stdio.h> int main(void) { // Declaration and assignment of the variable a char a = 100; // Add 1 to the variable a a = a + 1; // Display the final value of a printf("100 + 1 = %d", a); return 0; }

Exercise 4

Write a program that:

• declares a variable nb_student of type short
• assigns the value 1234 to this variable
• displays the nb_student variable

#include <stdio.h>

int main(void) {
    // Declaration and assignment of nb_student

    // COMPLETE HERE

    // Display the variable

    // COMPLETE HERE

    return 0;
}

#include <stdio.h> int main(void) { // Declaration and assignment of nb_student // COMPLETE HERE // Display the variable // COMPLETE HERE return 0; }

Quiz

To store a value in the range [-100 ; +100], which type is the most suitable?

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Which type is best suited to memorize a 4-digit credit card code?

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Which type is best for string a person's age?

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Is the size of an int 4 bytes?

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What is a signed number?

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What is the largest value that the variable i will hold?

unsigned char i;

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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 2.3. 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 5.5. switch..case statement
• 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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