Transcript Intro to C language - California State University, Los Angeles

Tarik Booker
CS 290
California State University, Los Angeles

This class is taught in the C language

The book is written in the C++ language
◦ Not (exactly) the same language
◦ Very similar

Look at lecture first before looking at book.

Introduction to C

Variables

Data Types

Intro to C

You should now have:
◦ Code::Blocks working and accessible
 (Code:Blocks or Xcode for Mac users)
◦ The basic “Hello World” sample program that came
with the Code::Blocks

Lets look at that main.c program.

Lets look at that main.c program.
File
Headers
Main
Function
C Code

The simplest program in C:
int main()
{
}

Doesn’t do anything!!!
int main()
{
}

What does this mean?
◦ Main = most basic function
◦ Function = piece of written code
 “Our” function
 Doesn’t do anything

Functions:
◦ Pieces of code that run
◦ Main
 Special function that runs first!
 All C programs must have a main function
 The type that is before specifies a return type (the type
of value the function should result in)
 Normally main should return some value (using the return
keyword), but C lets you omit it in main
int main()
{
}

Curly Braces
◦ {}
◦ Signals the beginning and end of functions
◦ Also other code blocks
 Note: Nothing in between curly braces here, so nothing
happens (executes)

Back to main.c
◦ “Hello World” is the most basic program
 Main function
 Now there’s code
 File Headers
File
Headers
Main
Function
C Code


Include statements
“Header” files
◦ Compiler copies and pastes everything in the
header file to your code
◦ Access to basic functions
 Stdio
 Standard input/output functions
 Stdlib
 Standard library functions
◦ Can even create your own header files!

Using a file header:
◦ Use #include <headername>
 Put the header name between the <>
 These are really “.h” files
 Built in files omit .h
 Non-standard files are different:
 #include “math.h”

Now we know:
◦ Main Function
◦ File Headers

Printf?
File
Headers
Main
Function
C Code

Print formatted data
◦ To Standard Out (stdio)
◦ Prints a formatted String (characters and text) to
the screen
 printf(“This should display in my results.”)
 The backslash-n (\n) will print a new line
 \ - called an escape character
 “Escape” from the current mode

What do these display?
 printf(“Hello there!”);
 printf(“Hi! \n My\n Name\n Is…”);

Can store values to be used (later) in a
program
◦ Values can be changed
◦ Remember algebra:
 x + y = 34
 y=5
 x =?
◦ Similar Concept in Programming

You must declare a variable in a program
before you use it
◦ Format:
 datatype variableName;
 A variable can be of any name
 Follow identifier rules (later…)
 Descriptive names are best

Datatype variableName;
 Datatype variableName1, variableName2,
…,variableName3;

Datatype




Specific classification of variables
Different types / different memory sizes
int, double
(main ones)
Discuss later

To name variables or functions
◦ Called identifiers
 Should obey rules:
 Consists of letters (upper/lower), digits, underscores
 Must start with a letter (alphabetic character)
 Must NOT start with a digit!!!
 Cannot be a reserved word (int, return, main, etc.)
 Can be up to 31 characters

Which are legal?








helloworld
aadzxvcna343546390thjke456hftg3sd
HappyHappy
34joy56
$Dollarsand
return
mains
#love
 Why / Why not?

After declaring a variable, you must assign it
a value.
◦ Use the assignment operator (=)




int myNumber;
myNumber = 1;
Assigns the value 1 to variable myNumber
Note: You can assign a value to a variable in the
variable declaration statement!!!
 Ex:
 int myNumber = 1;
 double volume = 3.0;

Assigning a value to a variable results in an
assignment statement
◦ double volume = 5.0;

You can also assign the results of an
expression to a variable
◦ double volume = 5.0 * 3.0;
◦ int x = 5 * (3 / 2);

Either method initializes the variable
◦ Should initialize variable after (during) you declare
it!

You can use other variables inside of
expressions!
◦ Can also use the same variable!
◦ int x = 1;
◦ x = x + 1;
 Executes Right-Hand Side (RHS) first, then assigns the
result to the Left-Hand Side (LHS)
 What is x after the code?


Variable values can change during a program
(Named) Constants are permanent
(throughout the life of the program)
◦ You can define constants
◦ Use the const keyword (either before or after the
datatype)
 const datatype constantname = value;
 datatype const constantname = value;
 Ex:
 const double PI = 3.14159;
 int const x = 5;

(Numeric) Data Types represent different
ways to store numeric values in a variable
◦ Variables are stored in (primary) memory
◦ Different data types take up different spaces in
memory

Integer Data Types
◦ Used to store integers
 …, -10, -9, …, -3, -2, -1, 0, 1, 2, 3, …, 9, 10, …
 int
 long
◦ Many more (will discuss later…)

Floating-Point Data Types
◦ Written in Scientific Notation
 Mantissa
Exponent
 double
 float
 (Will discuss later…)

C includes standard arithmetic operators




Addition
Subtraction
Multiplication
Division
+
*
/

Also has modulus (%)
 Also called the remainder operator
 Gives the remainder after division







6%2 (Say 6 “mod” 2)
What is 6%2?
3%1
1%3
10%5
Any even number % 2?
Any odd number % 2?
 Can use this to check evens or odds

Use the pow(a,b) function
◦ Requires double type
◦ Returns ab
◦ Must include math.h
 #include <math.h>
◦ Ex:
 double y=1.0;
 y = pow(2.0,3.0);

Literal – Constant values that appear in a
program
◦ Ex:
◦ Or:
int numberOfYears = 34;
double weight = 0.305
 34 and 0.305 are literals
◦ Different types of literals
 Integer
 Floating-Point

Integer Literals:
◦ Can be assigned to an integer variable
◦ Works so long as it is within the range of the
variable type
◦ Assumed to be type int (32-bit range)
◦ For type long, append the letter L to it
 Ex: 2145063967L

Can also use binary integer literals
 Start with 0B or 0b (zero b)
 Ex: 0B1111 results in 15

Also can use octal (base 8) and hexadecimal
(base 16) integer literals
 Octal: Start with 0
 Ex: 07777
results in 4095
 Hex: Start with 0x or 0X (zero x)
 Ex: 0XFFFF results in 65535

Floating-Point Literals
◦ Written with a decimal point
 Ex: 5.0
◦ Default is double
 Make literal float by adding an f
 Ex: 100.2f
 Note: double has more significant digits (15-18)than
float (7-8)

You must use the percent sign (%) when
printing a variable
◦ Use the percent sign and a code for the type
 %d
 integer
 %lf
 double
 %f
 float
◦ Use the code within the String, then after, use a
comma, and the variable name

Ex:
◦ int x = 1;
◦ printf(“The result is: %d”,x);
◦ double y = 3.0;
◦ printf(“The result is: %lf”,y);


You can take any mathematical expression
and translated into code
Make sure you use parentheses whenever
appropriate
◦ Ex:
z=
◦ Result:
3+4𝑥
10
+
10(𝑦−3)
7
4
− 9( )
𝑥
 z = (3+4*x)/ 10 + 10 * (y-3) / 7 – 9*(4 / x);

What’s the order of operations?
◦ PEMDAS
◦ Please Excuse my Dear Aunt Sally
◦ Parentheses, Exponent, Multiplication, Division,
Addition, Subtraction
◦ Equal operators (M, D, and A,S) go from left to right

You can combine arithmetic operators and
the assignment operator to perform
augmented operators!!
 Ex: x = x + 1;
 1 is added to x, and the result is put back into itself
 Will happen often (later)
 Can shorten this to:
 x += 1;
 This is translated as x = x + 1;
 Works for other operators

Addition
◦ x += 1;
 Result: x = x + 1;

Subtraction
◦ x -= 5;
 Result: x = x – 5;

Multiplication
◦ y *= 3;
 Result:

Division
y = y * 3;
◦ volume /= 7;
 Result: volume = volume / 7;

Remainder
◦ i %= 5;
 Result: i = i % 5;

Shorthands for incrementing and
decrementing variables;
◦ ++, - ◦ Adds (++) or Subtracts (--) by one
 Ex: int i = 3;
 i++;
 Result?
 Ex:
 z--;
int z = 4;
◦ Can put before (++i) or after variable (z--)

If used alone (i++, or --z) direction doesn’t
matter.
◦ Ex:
◦ or:

++j;
j++;
// Doesn’t matter
If used within an expression (or statement),
direction does matter

Preincrement / Predecrement
◦ Ex:
++var
--count
◦ If used within an expression, the variable is
incremented (or decremented) first, then used in
the statement
◦ Ex:
int j = ++i;
 If i is 2, what is j?

Postincrement / Postdecrement
◦ Ex:
var++
count-◦ If used within an expression, the variable is used in
the statement first, then incremented (or
decremented) afterward
◦ Ex:
int j = i++;
 If i is 2, what is j?
 What if i is 6?