User Interaction and Variables Tarik Booker CS 242 California State University, Los Angeles

What we will cover… Review Data Types Standard Input

Variables 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

Variables (2) 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

Variables (3) Datatype variableName; Datatype Datatype variableName1, variableName2, …,variableName3; Datatype Specific classification of variables Different types / different memory sizes int, double (main ones) Discuss later

Variables (4) Variables are Case-Sensitive in C Uppercase and Lowercase Not the Same “Variable1” is not the same as “variable1”

Identifiers 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

Identifiers (2) Which are legal? helloworld aadzxvcna343546390thjke456hftg3sd HappyHappy 34joy56 $Dollarsand return mains #love Why / Why not?

Char There is another type of variable other than integers or floating-point Char Allows you to store a single character Uses ASCII American Standard Code for Information Interchange Each character is assigned to a particular number ASCII Table ‘A’ is 65 ‘a’ is 97 Lowercase is higher than Uppercase Add 32 to change an uppercase letter to lowercase Subtract 32 to change a lowercase letter to uppercase

ASCII Table

Reading in a Value from Standard In Before, we used a function to send information to Standard out What was it? Now we can get information from Standard in Let’s get a character from standard in Use the scanf() function

Scanf A way to input data into the computer is to use scanf This can “scan” in characters from the console Format similar to printf int x; scanf(“%d”, &x); This puts the value of %d into x Different types for % (called format specifiers) %d = decimal (integer) %c = character We will talk about others later…

Scanf (2) Note the & sign before the x int x; scanf(“%d”, &x); This is a pointer reference Outside the scope of this class Passes to scanf the memory address of the variable x Keep the same format – don’t worry about pointers

Data Types Char is considered a data type A data type is just the way information is stored in the program char, int, float, double, void (will discuss) are called primitive data types or primitives Other types of primitive data types

Data Types Char Character Int Integer Double Double Precision Floating-Point Void no type (or empty) Void Use this data type when no type is expected Primarily used for functions to specify not a return type Look at main

Data Types (2) C has many many different types of basic (or primitive) data types Different versions of char, int, long, double Char Signed char uses signed version of char Unsigned char uses unsigned version of char

Data Types (3) Short 16-bit integer type Short int Signed short Signed short int Unsigned short Unsigned short int

Data types (4) Int Signed int Unsigned Unsigned int Long long integer (at least 32 bits) Long int Signed long Signed long int Unsigned long Unsigned long int

Data types (5) Long long 64-bit integer Long long int Signed long long Signed long long int

Data Types (6) Float Double Long double There are also other types: Boolean (next week) True/False

We will do in class work today! Let’s do some problems!