EE160 Programming for Engineers

What are variables?

• holds information that can be changed

Why use variables?

• programs with information that's predetermined is not very useful

How to use variables?

• declare variables
• initialize variables
• set, change, or display variables

What are data type's?

• data types specifies what type of information is stored by the variable
• C has many type's available, they are listed here

Why use data type's?

• so the program knows how much memory to allocate and how to interpret the allocated memory
• C requires all variables to be type'd
• some programming languages don't require type'ing
• here's an article on dynamic vs static type'ing, you can just read the conclusion

How to use data type's?

• to declare an integer number: int i_am_an_integer;
• to declare a character: char i_am_a_char;
• to declare a decimal number: float i_am_a_float;
• to declare a decimal number with higher precision: double i_am_a_double;

variables.c:

Things to note:

• printf needs the conversion specifier to know what type the variable is
• the conversion specifiers are listed http://en.cppreference.com/w/c/io/fprintf
• the conversion specifiers can be formatted with optional flags listed at http://en.wikipedia.org/wiki/Printf_format_string#Format_placeholder_specification (Section Format Placeholders)
• printf is not very smart and will do exactly as you tell it, so if you are not careful errors can propagate throughout your program
• char's has a int representation, http://www.asciitable.com

Homework Problem 3.1, at the end of this problem you should submit to Laulima:

• a file named UHusername_03_1.c

  example:

  • zhaol_03_1.c

• Write a program that:

  • initializes a variable to 1.2345
  • and outputs the following by using just that variable and printf

    zero padding in back of a number: 1.23450 1.234500 1.2345000
    zero padding in front of a number: 1.2345 01.2345 001.2345
    exponentials (base 10): 1.2345e+00 1.23450e+00 1.234500e+00
    truncation vs rounding of numbers: 1.234 
    negative numbers: -1.2345 -1.2345e+00

  • Note that the exponentials is still displayed from a single variable. It is not a concatenation of numbers and characters
  • To convert the variable to a negative number just multiply it by -1 when you pass it to printf, like this -1*your_variable
  • Do not "hardcode" characters into the output, such as printf("00%f", variable);
  • If you are stuck, you can use the following template: