Terms to know:

  • Syntax – Rules for writing a program in a particular language.
  • Operator – Symbol representing a function that calculates a value.
  • Operand – Value to the left or right of an operator.
  • Promotion – Changing the data type of a variable so that it can hold more information.
  • Demotion – Changing the data type of a variable so that it loses information.
  • Type Casting – A way to temporarily and explicitly change the data type of a variable.

How C code compiles: User written code -> Object file (processor specific) -> Linker Compiles code -> Machine code (executable) Compilation

#include <stdio.h>

The code above is a compiler directive telling the compiler to include stdio. Compiler directives start with an # so #define is also a compiler directive.

The #define directive will substitute the assigned value whenever its mentioned. You cannot put a ; at the end of a define

Main Function

  • It is required for all C programs in windows. (Maybe compilers allow for other methods but not important for this course.)
  • The magical starting point for all of our code.

Language (Vocab) Errors in syntax are called compile time errors because the compiler reports them.

Variable Naming Conventions#

  • Variables cannot start with numbers. Ex: 7days.
  • They can only contain the characters a-z, A-Z, 0-9.
  • Use appropriate naming for the use of the variable.
  • Use mixed case for readability.

Random Operator Notes:#

Modulus returns the remainder of division. It’s frequently used to find if a number is even by dividing by two. It’s not limited though.

Variable Reference Table#

Reference Table

Remember this:

  • Smallest whole number – char (1 byte)
  • Second smallest whole number – short (2 byte)
  • Second largest whole number – int (4 bytes)
  • Largest whole number – long long (8 bytes)
  • Smallest decimal number – float (4 bytes)
  • Largest decimal number – double (8 bytes)

The keyword unsigned can only be used with whole numbers.

  • It causes the RANGE of the variable to change.
  • Moves from having negative numbers to starting at 0.

The char datatype

  • Smallest datatype at 1 byte.
  • The single characters in a char are represented with single quotation marks like 'x' but even with a character there is a number in the char variable.
  • The complier will translate the numbers in a character into text using the built in ascii table.

Operator Data Types:

  • Compiler pick the data type of the operator based on the type of operands
  • Some examples of data type division:
    • (int) / (int) will result in integer division.
    • (double) / (double) will result in double division.
  • Mixed division:
    • (int) / (double) or (double) / (int)?
    • The integer will be promoted to double.
    • (int) -> (double) / (double)

Assignment Operator Assignment Operator Continued

Lecture 2#

There are lots of options to format output of variable values.

  • %i for int values
  • %lf for double values. (This is ell eff)
  • %.2lf specify the accuracy – places past the decimal.
    Instead of output 3.33333333 would output 3.33

scanf syntax:

scanf("Sequence", &variable);

  • you must specify the sequence of the variable you are inputting data into.

    • %i for integers
    • %if for doubles

  • Do not use \n or %.2lf or any special input characters. Why? The scanf method wasn’t designed to handle them

  • scanf pauses the program but will not tell the user the input. (the sequence section ) special characters variable table

IO Summary#

  • Output information going from the program to the user
  • Input information going from the user to the program
  • printf and scanf
  • Escape characters are used to control the position of the output cursor, and to output some special characters
  • % sequences, correspond to the variables that are being input or output, and can be modified for formatting the output.
  • You can specify the data type of the input, and the type and format of the output.
  • Use the documentation for your compiler – search for “Format Specification Fields.”
  • Don’t forget the & on the variable name for input!
  • A “Prompt” is a message that tells the user what the program is expecting them to enter.

Relational Operators:#

  • Relational Operators by themselves aren’t typically used.
  • They create a relational expression that can be used with other functions in C, such as the if statement.
  • if expression is tied to the code that immediately follows it.
  • Decides if the code is executed or not.
  • if(TRUE) then the code is executed.
  • if(FALSE) then the code is skipped.

Switch Statements: They compare the value of a variable with a bunch of different cases. These cases are called control paths.

Ternary Operator: Allows for short hand writing of conditional logic. The ternary operator is ? so the lines will look like (x==y) ? run() : stop();

Rules of Precedence:

  • ! has the highest precedence
  • && when AND and OR occur in the same expression && has a higher precedence.
  • || has the lowest precedence of the operators.
  • Example:
    • a > b || c == d && a < d # do relational first
    • TRUE || FALSE && FALSE # next the AND
    • TRUE || FALSE # lastly the OR
    • TRUE
  • Parenthesis can be used to specify the order of precedence

Post and Pre increment:#

You can do:

  • a++ post increment.
  • ++a pre increment.

What does it matter?

  • Determines WHEN the increment or decrement occurs.
  • Pre-Increment occurs BEFORE all other calculations.
  • Post-Increments occurs AFTER all other calculations.

b = ++a;

  • Add one to a then assign to b. b = a + 1

b = a++;

  • Assign a to b then add one. b = a Often you do the increments and decrements by themselves.

Summary#

  • There are three logical operators:
  • And &&, Or ||, Not !
  • Can be used to express more interesting conditions
  • Precedence Not, And, Or
  • True and False are numeric in C. Zero is False, Non-zero is True
  • New Operator: compound Assignment +=
  • a = a + b; a += b; often used for accumulators
  • New Operator: increment ++ decrement –
  • Pre, and post increment and decrement
  • ++ and – break the usual rules of precedence.

Lecture 3#

Building Loops#

int x = 0;
while(x < 10)
      x++;
  • Always ask, where does the loop begin?
  • What value did the variable start with?
    • x starts at 0.
  • Where does the loop end?
  • What causes the relational expression to go false?
  • Once x is greater than or equal to 10.
  • How do we get from beginning to end?
  • What causes the variable to CHANGE within the loop?
  • x++ will increment the variable one at a time.

Counters and Accumulators:

  • Counters – Variables used within a loop to count by a set amount.
  • Accumulators – Variables within a loop that accumulate data over the loop.

Sentinel and Counter Controlled loops:

  • Sentinel controlled loops run until the sentinel is changed to top the loop.
while (count < 10)  // A counter controlled loop

while (testScore != -1)  // A sentinel controlled loop

Do While Loops:

  • They are post-test loops that execute code first then check if the need to keep executing after evaluating a condition.
  • Which is different then pre test loops which evaluate conditions before executing code. do-while-loops

For Loop Execution Chain for-loop-exec

Loops Summary:

  • Sequence, Selection, Repetition (looping)
  • Counter and Sentinel controlled loops
  • Start 2. Stop 3. Get there
  • Counter variables, Accumulator variables
  • Use a test case, and step through the code in the debugger to see its behavior
  • while
  • Pre-test loop
  • Often used for sentinel controlled loops
  • do-while
  • Post-test loop - generally frowned upon, but may be useful in some circumstances – when you learn the status of the stop condition in the body of the loop.
  • Used for counter controlled loops. Very commonly used.
  • Use while for sentinel controlled loops.

Random Numbers#

  • Brief lesson in generating random numbers.
  • C uses an algorithm that takes a starting number and generates a set of random numbers to be called.
    • The starting number is called a seed.
    • If you give the same starting number, you get the same set of random numbers (pseudo-random).
  • Commonly you use the current time as your seed.
    • In C time is represented as a single integer.
    • This integer is the number of seconds since January 1st, 1970.
    • This causes a new set of random numbers every time your program runs.
  • srand(starting number) – seed function
  • time(NULL) returns the current time.
    • Need to #include <time.h>
  • rand() – Get the next number in the random set.
    • returns a number between 0 and 65K.
    • Usually you constrain its range with % and addition
    • rand() % 6 will result in a random value from 0 to 5.
    • rand() % 6 + 1 will result in a random value from 1 to 6.

Generate a random number from 1 to 6 (a dice roll).

  • Repeat this 1000 times.
  • Count how many times a 1 is seen.
  • Output the percentage of times 1 was seen (count / 1000).
  • Run the program again 10000 times, 100000 times.

Arrays:

  • You cannot change the size of the array after it is declared.
  • The size of the array must be a positive integer
  • The size of the array must be a constant (not a variable)
  • The index for the array must also be a positive integer
  • It helps to draw pictures of the array you’re working with

Strings:

  • Strings are slightly different than int or double arrays.
  • They can be initialized with “ “
  • They need to be the number of possible characters + 1
    • A special character \0 is used at the end of every string to signify its end.
  • Inputting Strings:
    • %s is used to print strings.
    • scanf is also bad at inputting strings use get instead.