COMP 208- Midterm Review

Precedence of arithmetic operators in C

*/% take precedence over +- Will evaluate */% before +- For operators of same precedence it reads from left to right

What is a function?

-A group of statements that together perform a task -Can divide code into multiple functions -C has multiple built in functions, such as **main**

How to declare variables

-Variable name cannot start with a number -Variable name cannot have spaces can also initialize variable when you declare it: int age = 21; or you can leave it uninitialized: int x, y, z; float c, f, h; FORMAT- float variable_name = 0; the variable variable_name is equal to zero

Void function

-We use this to make a function that *will not return any values* -We can use this to create *internal changes* (change values of variables... etc)

Inserting a comment

//comment// not included in C program

Generating Random Numbers- Between 0 and 32767

1) Must have # include <time.h> and # include <stdlib.h> Use: srand(time(NULL)); printf("%i", time( ));

Generating Random Numbers- Between a and b

1) Must have # include <time.h> and # include <stdlib.h> 2)Must have srand(time(NULL)); in code RANDOM INTEGER: int x; x=rand()%(b-a+1) + a; RANDOM FLOAT: float x; x=(float) (b-a)rand()/RAND_MAX + a;

How to use a break/ general form

A break will END A LOOP (only used in **loops**) Write a break WITH AN IF STATEMENT if the condition in the if statement is true, loop will terminate and compiler will move on to the next statement *General Form:* if (condition) {break; }

What is a pointer?

A variable whose value is the ADDRESS of another variable General form: *var_name Write it in like a normal variable; int a; int *pa = &a; Pointer name must be different from original variable name Remember to use & when assigning pointer

What is the use of a file?

Allows you to open large amounts of binary data at once Must assign the file a *file pointer*: FILE *name output the data from the file using printf input the data from the file using scanf

int main( ) { }

Basic built in function that every function must have C knows that it is the entry point of your program int- data type for integer main- name of function brackets- take an ARGUMENT

How to call a function

Calls the function to perform its task for specific variables Create a main function that defines the specific variables and gives the return value based on the defined function Example: int myfunction(int, int); int main( ) { int x; int y; int result; printf("enter values for x and y\n"); scanf("%d %d", &x, &y); result = myfunction(x, y); printf("%d\n", result); return 0; }

Bubble sort algorithm

Compares the first two elements of an array and swaps them if necessary, then continues to next two etc, sorts the algorithm into ascending order

How to use continue/ general form

Continue will skip remainder of loop statements Returns function to the *TOP OF THE LOOP* Example: for (i=1; i<=8; i++) { if (i==3) {continue;} printf("Hi \n"); } function will print Hi for all values except for i=3 General form: if (condition) {break;}

For loop: simplifying increment

Example: for (i=1; i<=5; i++) { printf ("%i", i); } i++ indicates that i will INCREASE BY ONE each loop; i=i+1 i-- indicates that i will DECREASE BY ONE each loop; i=i-1 i+=3 i=i+3 i-=5 i=i-5 i*=4 i=i*4 i/=3 i=i/3

Declaring multi dimensional arrays

Example: int b[2][3]; Yields 6 different memory cells because there are 6 different permutations, useful for matrices b[0][0] b[0][1] b[0][2] b[1][0] b[1][1] b[1][2]

do... while loop

Form: do { expressions } while(condition); Will do the expression once before it tests the condition

How to dereference a pointer

Gets the value of the variable that you are pointing to Use placeholder of original variable (%d, %i, %f...) with the pointer and it will return variable value example: int main() { int i= 17; int *pi = &i; printf("%d\n",*pi); return 0; }

Declaring a function

Goes at TOP OF CODE with function in it Is necessary to declare a function in the top of your code so function can be read in different source files **FORM** return_type function_name( parameter list ); -Do not need to include parameter names when declaring function, just parameter types **Example: ** for a function- int max (int num1, int num2) { body} declaration: int max (int, int);

%d

Is called a PLACEHOLDER Will hold an INTEGER

%f

Is the placeholder for a FLOAT

Sorting algorithm

Means to put all the elements of an array in ascending order Can be done using bubble sort or selection sort

How to use integers in arguments

Must use a placeholder Example- printf("the number is = %d", 32);

swap function in C

No simple swapping function exists, must create a function like this void swap(double *a,double *b) { double temp = *a; *a = *b; *b = temp; }

%c

Placeholder for a CHARACTER

%p

Placeholder for a pointer, used for referencing MEMORY ADDRESS OF ELEMENT, from pointer Must use & when defining it

#include <math.h>

Provides all math functions

Optimized bubble sort algorithm

Puts the elements of the array into ASCENDING ORDER, does this by comparing elements two at a time, putting larger one last

Binary Search in C

Quick version of linear search array must already be SORTED

Selection sort algorithm

Scans part of the array and finds the minimum value, puts that minimum value at the beginning of the selection, moves up by one each time until the array is sorted

How to open a file?

Use function *fopen( )* Form: var= fopen("file_name", "mode") *mode*- tells compiler what to do with file w= write, clears file and writes over it every time r= read, need scanf a= append, doesn't erase but you can add to file

#include <time.h>

Use in random number problems with time(NULL);

Nested if statements:

Use it to check multiple conditions within one statement Example: if(age>18) { printf("age is greater than 18\n"); if(age<21) { printf("age is greater than 18 but less than 21\n");} } **will print both statements if user inserts something between 18 and 21**

%s

Used as placeholder for a STRING String= text like "hello world"

Ternary Statements

Used to SIMPLIFY IF STATEMENTS Form: (expression, if condition) ? (if condition is true) : (if condition is not true) If condition is true, first parameter is returned If condition is false, second parameter is returned

Modulus function in C

Used to check what the remainder will be for the division of integers, can see if a number will be perfectly divisible Useful to check if a number is even or odd if (number % 2 == 0) { printf("%d is even", number); }

Linear Search in C

Used to see if a value is present in an array and where it occurs Array DOES NOT NEED TO BE SORTED

#include <stdlib.h>

Useful functions such as calloc, malloc, free, exit, srand, rand, abs

When to use & symbol

Whenever you want to print out a memory address When assigning values to variables using scanf

printf("Hello World\n") ;

\n- indicates CHANGING OF A LINE Function will print Hello World

Pointers and array

array name is the POINTER to the first memory element of the array

For loop: Basic form

for ( init; condition; increment ) { statement(s) } Will create a **loop** Statement will keep on repeating until CONDITION IS FALSE Increment- amount the variable will change each time loop is run

If statements: form

if(condition) {code to execute} If condition is true, then code will execute If condition is false, compiler will move on to next statement can use else statement to have a code to run for anything that doesn't meet any of the if conditions else statement- doesn't take any condition else {code to execute} else if statement: used to check multiple conditions use it after first if statement

Different types of variable declarations

int - used to store INTEGERS, %d float - used to store a DECIMAL, %f char - used to store a CHARACTER ('a'), %c double - used to store a LARGE DECIMAL, %lf

Writing a program that divides two numbers, a and b and prints answer

int main( ) { int a = 9; int b = 2; float division; division = a / b; printf("The answer = %f", division); return 0; } **Remember that answer must be FLOAT because it will have decimals**

%lf

placeholder for a DOUBLE- a "large float" value

%ld

placeholder for a LARGE INTEGER VALUE

Multiple integers in arguments

printf("the numbers are %d %d %d",32,8,5);

\t

puts a tab in when you print something, not a new line, just further along the line, useful for ARRAYS

return 0;

return statement must be at the end of function with int

How to define a function?

return_type function_name ( parameter list) { Body of function } **Return type** - is the type of value that the function will return (int, double, char, float), if the function does not actually return a value, the function type will be VOID **function name**- make sure to not use a name of an already defined function **parameters**- works like a placeholder, when function is invoked, pass a value to the parameter

#include <stdio.h>

stdio.h- basic library to be included at beginning of programs Responsable for things like printf function

Declaring single dimension array

type array_name [array_size] array_size- must be an integer Must declare the type of variable in array when declaring it Example: double balance [5] = {100.0, 5.0, 2.7, 3.2, 5.4} Example: int a[5]; will yield- a[0] a[1] a[2] a[3] a[4] **notice it will start at zero and end at n-1**

scanf( );

used to take the INPUT from the user will store the input into a VARIABLE type of variable and placeholder MUST MATCH scanf("%lf", &variableName) reads a user-entered value and stores the value into the given variable *remember to use & to ASSIGN VALUE TO VARIABLE* Will scan whatever you type into compiler

When to use ==

when we want to compare variable to number without assigning that number to it. useful in if statements: if (age == 18) { printf("You are 18 years old"); **in this case age is a variable that we input using scanf**