Variables, Data Types, and Arithmetic Expressions Learning Objectives: Printing more than one variable in one printf() Printing formatting characters in printf Declaring and initializing variables A couple of Variable types Input and output of float or double variables Arithmetic Operators you ve probably seen Integer Division Modulus Operator Expressions in printf() Assignment Operator 1
printf() continued Review: printf( You are %i years old\n, age); You can print more than one variable in a single printf(): Example: printf( x = %i, y = %i, z = %i\n, var1, var2, var3); To print formatting characters (% or \), double them up: Example: printf( The percentage is %i%%.\n, perc); If the value of perc is 85, then the output would be: The percentage is 85%. To print a \: Use \\ 2
Declaring and Initializing Variables Variables can be many different types, for example integers, strings, real numbers, even students. Each type will have it s own set of properties and you have to specify the type so the compiler knows how to treat it. For example, integer division is different from real number division. Syntax: variable type then variable name then (optionally) assign a value to the variable Example: int age; //declares an integer variable called age When you declare an integer, you give it a type and a name and the program gives it a memory. address You can also give it a. value Example declaring and Initializing age: int age = 20; //initializing means assigning its first value Remember: No spaces or special characters in variable names! 3
Declaring Variables You can declare more than one variable on the same line: Examples: int age, apples; //declares both age and apples as ints int age=20, apples=53; //also initializes age and apples Note: Once a variable is declared, you don t ever re-declare it. Some Basic Number Types and their limits: Note: unsigned is a modifier that can go with any integer type Integers Type Typical Limits short -32,767 to 32767 int -2,147,483,647 to 2,147,483,647 long -2,147,483,647 to 2,147,483,647 unsigned short 0 to 65535 Floating Point Type Typical Limits float 6 digits of precision, Max exponent = 38 Max Value = 3.402823e+38 double 15 digits of precision, Max exponent = 308 Max Value = 1.797693e+308 long double 15 digits of precision, Max exponent = 308 Max Value = 1.797693e+308 4
Examples: Declaring Variables (For numbers, you will use int and double mostly) //create a double variable called side1 and assign a value of 4.9 to it double side1 = 4.9; //create an integer variable called num and assign a 0 to it. int num = 0; //create an int variable called n2 that can t be negative unsigned int n2; //create two float variables and initialize them to 3.21 and 6.42, respectively float a = 3.21, b = 6.42; //create a double variable called x and assign 5.4 x 10 5 to it double x = 5.4e5; 5
Output of floats and doubles Example that outputs an integer: printf( The integer is: %i \n, myint); %i means you are printing an integer. %f means you are printing a floating point number %lf means you are printing a double %e means you are printing in scientific notation (float or double) Example that outputs a double: printf( The number is: %lf \n, mynum); By default, you will get 6 decimal places when you print a floating point or double variable. To modify that, use. as follows: Example that prints a double with 3 decimal places: printf( The number is: %.3lf \n, mynum); 6
Input of floats and doubles Inputting an integer variable: scanf( %i, &myint); %i means you are reading an integer. %f means you are reading a floating point number %lf means you are reading a double Example that inputs a double: scanf( %lf, &mynum); Do you need to worry about the number of decimal places with scanf? No the user will type in as many as he/she wants. 7
Some Basic Arithmetic Operators Multiplication: 2.2 * 3.0 Division: 2.2 / 3.0 Addition: 2.2 + 3.0 Subtraction: 2.2-3.0 Equal Sign: IMPORTANT: = is the assignment operator, so if you say: x = y + z //this will add variables y and z then assign that //value to x. Note: y+z=x doesn t work!!! Does everything to the right of = then assigns value to 8 variable on the left. You must have a variable on left.
Integer Division Variables have properties based on their type. This means that integers can act differently from doubles. This is especially important in the case of Integer Division. If the numerator and denominator are integers, the program will truncate the result. Examples: Give the value of x after each line executes: x = 10 / 3; x = 2 / 5; x = 3 x = 0 x = 1 / 2 * 3.14159 * 2.2 * 2.2; x = 0 9
Modulus Operator The modulus operator is a %: Examples: x = 21 % 4; y = 52 % z; r = s % y; The numbers or variables to the right and left of the % must be integers. The resulting value of a modulus operation is the remainder after you divide the left by the right. 10
Examples Using the Modulus Operator Give the value of x after each line executes: x = 10 % 3; x = 1 3 goes into 10 three times, leaving a remainder of 1 x = 2 % 5; x = 2 5 goes into 2 zero times, leaving a remainder of 2 Examples of where % is used: x%2 if this is 0, the number is even If this is 1, the number is odd If day 0 is on a Sunday, then day 1 is on a Monday etc. How can you use modulus to determine the weekday of day 123,455? int day = 123,455; int dayofweek = day % 7; (Note: I declared and calculated in one line.) 11
Expressions in printf() Example: printf( You are %i years old\n, thisyr - birthyr); Resulting value printed 12
Assignment Operator Revisited ( = ) This looks like an equal sign, but it is different than the equal sign you are used to!! The compiler marches line-by-line through the program. When it gets to an equal sign (assignment operator), it will: compute everything on the right-hand-side of the equal sign, take the resulting value, and assign it to the variable on the left Therefore, the only thing that can be on the left is a variable! What happens with each of the following statements? x + 2 = 4; Invalid You get an error message x = 3 + 7 * 9; Assigns 66 to x x = x + 3; Takes the value of x, adds 3 to it and reassigns the new value to x 13
Lab Work and Homework There is a lab for today and a Homework assignment due Monday at midnight. Submit the lab before leaving even if you don t get it completed. You will find the links to the lab and to the homework on Dr. Babcock s web page. The link for his web page is on the merged Blackboard course under External Links. Note: You will also find notes on how to download and install Cygwin and Notepad++ on your home computer if you look on Dr. Babcock s web page under Resources. My notes and other instructors notes will also be posted on Dr. Babcock s web page. Don t forget about the Pop Quizzes!! 14