Lecture 03 Primitive Datatypes

Joseph Haugh

University of New Mexico

Reading

Secs. 2.3-2.4 (pp. 60-65)
Online Appendix E (On number systems)
On the slides (may be found on C manual)
Integer datatypes

Programming in C

/* File: simple1.c */
/* Author: Joseph Haugh */

/* Forward slash and asterisk to open/close comments */

#include <stdio.h>

int main() {
    printf("Hello world!\n");
    printf("How are you today?\n");
    return 0;
}

$ gcc simple1.c
$ ./a.out
Hello world!
How are you today?

Simple program
2 lines of output

Programming in C

/* File: simple1.c */
/* Author: Joseph Haugh */

/* Forward slash and asterisk to open/close comments */

#include <stdio.h>

int main() {
    printf("Hello world!\n");
    printf("How are you today?\n");
    return 0;
}

$ gcc simple1.c
$ ./a.out
Hello world!
How are you today?

Simple program
2 lines of output
To understand C we must learn about the:
- Reserved words
- Operators

Reserved Words in C

auto	double	int	struct
break	else	long	switch
case	enum	register	typedef
char	extern	return	union
const	float	short	unsigned
continue	for	signed	void
default	goto	sizeof	volatile
do	if	static	while

All lowercase, these words cannot be used for anything else

Reserved Words

/* File: simple1.c */
/* Author: Joseph Haugh */

/* Forward slash and asterisk to open/close comments */

#include <stdio.h>

int main() {
    printf("Hello world!\n");
    printf("How are you today?\n");
    return 0;
}

$ gcc simple1.c
$ ./a.out
Hello world!
How are you today?

Which reserved words do you see?
Reserved words have special meanings
All programs are built-up by combining reserved words and operators

Primitive Data Types

/* File: simple1.c */
/* Author: Joseph Haugh */

/* Forward slash and asterisk to open/close comments */

#include <stdio.h>

int main() {
    printf("Hello world!\n");
    printf("How are you today?\n");
    return 0;
}

$ gcc simple1.c
$ ./a.out
Hello world!
How are you today?

We are often interested in data
We start with primitive data types
These are built-into C using the reserved words
An example in this program: int

Primitive Data Types

auto	double	int	struct
break	else	long	switch
case	enum	register	typedef
char	extern	return	union
const	float	short	unsigned
continue	for	signed	void
default	goto	sizeof	volatile
do	if	static	while

Reserved words relating to primitive data types in C

Primitive Data Types

Integers: ℤ = {…, −3, −2, −1, 0, 1, 2, 3, …}
Natural Numbers: ℕ = {0, 1, 2, 3, …}
Real Numbers: $$ \mathbb{R} = \{ \dots, -3.4, 0, \frac{7}{5}, e, \pi, 572.5683, \dots \} $$
Characters: {A, B, C, 1, 2, 3, @, #, … (all keyboard symbols)}
Booleans: {true, false}
Pointers:

How do we represent numbers?

Consider the number, or value, 3,682
How can we “write down” this value?
Ordinary representation:
- 3,685
- 3685

How do we represent numbers?

Consider the number, or value, 3,682
How can we “write down” this value?
Ordinary representation:
- ~~3,685~~ (no commas in numbers allowed in C)
- 3685
Roman Numerals: MMMDCLXXXV

How do we represent numbers?

Consider the number, or value, 3,682
How can we “write down” this value?
Ordinary representation:
- ~~3,685~~ (no commas in numbers allowed in C)
- 3685
Roman Numerals: MMMDCLXXXV
Scientific Notation:
- 3.682 * 10³
- 3.682E3
All the same value, but different representations

Number Systems

Read: Appendix C

Number Systems

Roman (Additive)
- I, V, X, L, C, D, M
Modern, aka Hindu-Arabic (Positional)
- 0, 1, 2, 3, 4, 5, 6, 7, 8, 9

Number Systems

Roman (Additive)
- I, V, X, L, C, D, M
- shape of the symbol indicates its value
Modern, aka Hindu-Arabic (Positional)
- 0, 1, 2, 3, 4, 5, 6, 7, 8, 9
- position of the symbol indicates its value
  - 246: two hundreds, four tens, and six ones
  - 462: four hundreds, six tens, and two ones
  - 402: four hundreds, and two ones
Four hundred and two
- Roman: C C C C I I (don’t need explicit 0)
- Modern: 402 (need explicit 0)

One Kind of “Zero” in C

auto	double	int	struct
break	else	long	switch
case	enum	register	typedef
char	extern	return	union
const	float	short	unsigned
continue	for	signed	void
default	goto	sizeof	volatile
do	if	static	while

Decimal vs Binary

Modern, aka Hindu-Arabic (Positional)
- 0, 1, 2, 3, 4, 5, 6, 7, 8, 9
- position of the symbol indicates its value
  - 246: two hundreds, four tens, and six ones
  - 462: four hundreds, six tens, and two ones
  - 402: four hundreds, and two ones
Computers are electronic
All data is represented with:
- 0’s
- 1’s
Must use binary, base 2 representation
Any value can be represented in different bases

Decimal vs Binary

462₁₀ = 111001110₂

Decimal - Base 10

3,642 in base 10 positional notation is:

$$ \begin{aligned} 3 \times 10^3 &= 3 \times 1,000 = 3,000 \\ + 6 \times 10^2 &= 6 \times 100 = 600 \\ + 4 \times 10^1 &= 4 \times 10 = 40 \\ + 2 \times 10^0 &= 2 \times 1 = 2 \\ &= 3,642_{10} \end{aligned} $$

Binary - Base 2

11010 in base 2 positional notation is:

$$ \begin{aligned} 1 \times 2^4 &= 1 \times 16 = 16 \\ + 1 \times 2^3 &= 1 \times 8 = 8 \\ + 0 \times 2^2 &= 0 \times 4 = 0 \\ + 1 \times 2^1 &= 1 \times 2 = 2 \\ + 0 \times 2^0 &= 0 \times 1 = 0 \\ &= 26_{10} \end{aligned} $$

Hexadecimal - Base 16

642 in base 16 positional notation is:

$$ \begin{aligned} 6 \times 16^2 &= 6 \times 256 = 1536 \\ + 4 \times 16^1 &= 4 \times 16 = 64 \\ + 2 \times 16^0 &= 2 \times 1 = 2 \\ &= 1602_{10} \end{aligned} $$

Binary and Hexadecimal

110011010₂ = 410₁₀

$$ \begin{aligned} 1 \times 2^8 &= 1 \times 256 = 256 \\ + 1 \times 2^7 &= 1 \times 128 = 128 \\ + 0 \times 2^6 &= 0 \times 64 = 0 \\ + 0 \times 2^5 &= 0 \times 32 = 0 \\ + 1 \times 2^4 &= 1 \times 16 = 16 \\ + 1 \times 2^3 &= 1 \times 8 = 8 \\ + 0 \times 2^2 &= 0 \times 4 = 0 \\ + 1 \times 2^1 &= 1 \times 2 = 2 \\ + 0 \times 2^0 &= 0 \times 1 = 0 \\ &= 410_{10} \end{aligned} $$

Binary numbers require many bits

Binary and Hexadecimal

110011010₂ = 410₁₀

Binary numbers require many bits

19A₁₆ = 410₁₀

$$ \begin{aligned} 1 \times 16^2 &= 1 \times 256 = 256 \\ + 9 \times 16^1 &= 9 \times 16 = 144 \\ + A \times 16^0 &= 10 \times 1 = 10 \\ &= 410_{10} \end{aligned} $$

Hexadecimal is more compact

Easy to convert from binary to hex and vice versa

Ints

Read: Appendix C

Creating Three Int Variables

/* File: 03_int.c */
/* Joseph Haugh */

#include <stdio.h>

int main() {
    int x = 12; /* declare variable */

    int someNumber = 45; /* declare variable */

    int foo_123 = 27455; /* no commas */

    printf("The value of x is %d\nsomeNumber = %d\n"
           "and foo is bigger\nwith value %d\n",
           x, someNumber, foo_123);
}

Create three integer variables
Print the value of the variables

$ gcc 03_int.c
$ ./a.out
The value of x is 12
someNumber = 45
and foo is bigger
with value 27455

Creating Three Int Variables

/* File: 03_int.c */
/* Joseph Haugh */

#include <stdio.h>

int main() {
    int x = 12; /* declare variable */

    int someNumber = 45; /* declare variable */

    int foo_123 = 27455; /* no commas */

    printf("The value of x is %d\nsomeNumber = %d\n"
           "and foo is bigger\nwith value %d\n",
           x, someNumber, foo_123);
}

printf begins with a formatting string (inside double-quotes)
this string spills over 2 lines
%d indicates a decimal value is to be printed

$ gcc 03_int.c
$ ./a.out
The value of x is 12
someNumber = 45
and foo is bigger
with value 27455

Creating Three Int Variables

/* File: 03_int.c */
/* Joseph Haugh */

#include <stdio.h>

int main() {
    int x = 12; /* declare variable */

    int someNumber = 45; /* declare variable */

    int foo_123 = 27455; /* no commas */

    printf("The value of x is %d\nsomeNumber = %d\n"
           "and foo is bigger\nwith value %d\n",
           x, someNumber, foo_123);
}

this string spills over 2 lines
%d indicates a decimal value is to be printed
For each %d in the printf, we list the corresponding value

$ gcc 03_int.c
$ ./a.out
The value of x is 12
someNumber = 45
and foo is bigger
with value 27455

Creating Three Int Variables

/* File: 03_int.c */
/* Joseph Haugh */

#include <stdio.h>

int main() {
    int x = 12; /* declare variable */

    int someNumber = 45; /* declare variable */

    int foo_123 = 27455; /* no commas */

    printf("The value of x is %d\nsomeNumber = %d\n"
           "and foo is bigger\nwith value %d\n",
           x, someNumber, foo_123);
}

Every data element (aka variable) has:
- Name or identifier
  - what do we call the variable, how do we “refer” to it?
- Address or location
  - where is this data located in the computer memory?

Creating Three Int Variables

/* File: 03_int.c */
/* Joseph Haugh */

#include <stdio.h>

int main() {
    int x = 12; /* declare variable */

    int someNumber = 45; /* declare variable */

    int foo_123 = 27455; /* no commas */

    printf("The value of x is %d\nsomeNumber = %d\n"
           "and foo is bigger\nwith value %d\n",
           x, someNumber, foo_123);
}

Every data element (aka variable) has:
- Type
  - what type of data is this (int, char, etc). How much memory does it take? ie., size?
- Value
  - what is the value of the data?

Graphical Representation

/* File: 03_int.c */
/* Joseph Haugh */

#include <stdio.h>

int main() {
    int x = 12; /* declare variable */

    int someNumber = 45; /* declare variable */

    int foo_123 = 27455; /* no commas */

    printf("The value of x is %d\nsomeNumber = %d\n"
           "and foo is bigger\nwith value %d\n",
           x, someNumber, foo_123);
}

It will often be useful to “draw” our variables

someNumber

foo_123

27455

Graphical Representation

/* File: 03_int.c */
/* Joseph Haugh */

#include <stdio.h>

int main() {
    int x = 12; /* declare variable */

    int someNumber = 45; /* declare variable */

    int foo_123 = 27455; /* no commas */

    printf("The value of x is %d\nsomeNumber = %d\n"
           "and foo is bigger\nwith value %d\n",
           x, someNumber, foo_123);
}

Every data element (aka variable, aka object) has:
- Name or identifier
- Address or location
- Type
- Value

someNumber

foo_123

27455

Identifiers are made from letters, numbers and _

Cannot start with numbers

Graphical Representation

/* File: 03_int.c */
/* Joseph Haugh */

#include <stdio.h>

int main() {
    int x = 12; /* declare variable */

    int someNumber = 45; /* declare variable */

    int foo_123 = 27455; /* no commas */

    printf("The value of x is %d\nsomeNumber = %d\n"
           "and foo is bigger\nwith value %d\n",
           x, someNumber, foo_123);
}

Every data element (aka variable, aka object) has:
- Name or identifier
- Address or location
- Type
- Value

someNumber

foo_123

27455

Where exactly are these variable stored on the computer??

You will start to learn where in this class.

Graphical Representation

/* File: 03_int.c */
/* Joseph Haugh */

#include <stdio.h>

int main() {
    int x = 12; /* declare variable */

    int someNumber = 45; /* declare variable */

    int foo_123 = 27455; /* no commas */

    printf("The value of x is %d\nsomeNumber = %d\n"
           "and foo is bigger\nwith value %d\n",
           x, someNumber, foo_123);
}

Every data element (aka variable, aka object) has:
- Name or identifier
- Address or location
- Type
- Value

someNumber

foo_123

27455

All three variables are of int

Graphical Representation

/* File: 03_int.c */
/* Joseph Haugh */

#include <stdio.h>

int main() {
    int x = 12; /* declare variable */

    int someNumber = 45; /* declare variable */

    int foo_123 = 27455; /* no commas */

    printf("The value of x is %d\nsomeNumber = %d\n"
           "and foo is bigger\nwith value %d\n",
           x, someNumber, foo_123);
}

Every data element (aka variable, aka object) has:
- Name or identifier
- Address or location
- Type
- Value

someNumber

foo_123

27455

The value is the actual data stored inside the computer memory.