CBasics_notes_2.exe

2D ARRAYS
- an array where each element is an entire array (matrix, grid or table of data)
// 2D arrays - datatype array_name[][] = {{},{}} (2 square brackets)
// we have to specify a max size for elements in each array 
// and setting max size for the whole array is optional
int numbers[][3] = {
    {1, 2, 3},
    {4, 5, 6}
    };
// accessing a certain element through index - array[index number of array][index of element in array]
// another way of assigning values 

int numbers2[2][2];
numbers2[0][0] = 1;
numbers2[0][1] = 2;
numbers2[1][0] = 3;
numbers2[1][1] = 4;
// numers2[0] - is he whole first row

int rows = sizeof(numbers2)/sizeof(numbers2[0]); // no. of rows - no. of arrays in 2D arrays (firsts square bracket)
int columns = sizeof(numbers2[0])/sizeof(numbers2[0][0]); //no. of columns - no of elements inside each array (second square bracket)

printf("\nRows: %d", rows);
printf("\nColumns: %d\n", columns);
// 2D arrays are accessed mostly through nested loops

for(int i = 0; i < rows; i ++)
{
    for(int j = 0; j < columns; j++)
    {
        printf("%d ", numbers2[i][j]);
    }
    printf("\n"); // new line after every inner loop iteration 
}

ARRAY OF STRINGS 
har cars[][10] = {"Mustang", "Corvette", "Audi"};
    // here each word is an array (second square bracket sets in a way max no. letters each string array can have)
    // the words cannot be dirscly assigned a new value

    //one way of assigning a new value is using strcpy() method
    strcpy(cars[0], "Tesla"); //str method where cars[0] (first array) is replaced by "Tesla"

    for(int i = 0; i < sizeof(cars)/sizeof(cars[0]); i++)
    {
        printf("%s\n", cars[i]);
    }

SWAP VALUES OF 2 variables
char x = 'X';
    char y = 'Y';
// to swap valus we could introduce a 3rd variable 
    char temp;

    temp = x; // temp is assinged X
    x = y; // x is assigned Y
    y = temp; // y is assigned X
    // x = Y, y = X

// it is a diff process fro strings - 
char a[] = "Anisha";
char b[] = "Hossain";
char temp_string[15];
// we use strcpy() operator

strcpy(temp_string, a);
strcpy(a, b);
strcpy(b, temp_string);

char x[15] = "Anisha";
char b[15] = "Meg";
char temp_string[15];

strcpy(temp_string, x);
strcpy(x, b); 
// when second string is smaller than first string it results in unexpected behavior when using strcpy()
// to solve this issue we can make all the char arrays the same size (all are assigned 15 in  square brackets)
strcpy(b, temp_string);

STRUCTS
- short for structures (collected of related variables)
they can be different data types listed under one name in a block of memory
Very similar to classes (but no methods)

//structs are created outside of main function - IMPORTANT
// format - struct Structname {code}; (have to use semi colon after)
struct Player
{
    char name[12];
    int score;
};

int main(){

    struct Player player1; // struct StructureName variable name
    struct Player player2;

    strcpy(player1.name, "Anisha"); // dot is a member access operator
    // if we are not working with a string of characters (array) we can access the variables directly
    // when working with arrays we alyways use strcpy to access or change values
    player1.score = 4;

    strcpy(player2.name, "Megha"); 
    player2.score = 5;

    //they can be displayed using printf
    printf("%s\n", player1.name);
    printf("%d\n", player1.score);

    printf("%s\n", player2.name);
    printf("%d\n", player2.score);

    return o;}

    ARRAY OF STRUCTS
    
    struct Student{
    char name[12];
    float gpa;};

int main(){
    struct Student student1 = {"Anisha", 4.0};
    struct Student student2 = {"Sophia", 3.8};
    struct Student student3 = {"Megha", 3.93};
    struct Student student4 = {"Bob", 2.7};

    struct Student students[] = {student1, student2, student3, student4};
    // array of structs

    // accessing the dot operator values of structs using for loop 
    for(int i = 0; i < sizeof(students)/sizeof(students[0]); i++)
    {
        printf("Student Name: %s\n", students[i].name); // displays their name
        // to not forget to use dot operator
        printf("GPA: %.2f\n", students[i].gpa);
    }
return 0;}


ENUMS
- (short for numerations) user defined type of named integer identifiers
(helps to make program more readable)

// enums can be created both inside or outside of main function
// format - enum Name{Constant1, Constant2, So_on}; (enums are constants)
enum Day{Sun = 1, Mon = 2, Tue = 3, Wed = 4, Thu = 5, Fri = 6, Sat= 7};
// by default the first constant is 0, second is 1 (like index) but we can also give them a unique value

int main(){
 // call format - enum variable_name = Constant;
    enum Day today = Sun;
    printf("%d\n", today); // enums are treated as integers not strings

if(today == Sun || today == Sat) // we can either use the integer or enum
{
    printf("Today is a weekend! party time!");
}
else{printf("I have work today :(");}
return 0;
}

RANDOM NUMBERS
- pseudo random numbers = a set of values or elements that are statitically random
#include <time.h> // incluse header for using random numbers

int main(){

srand(time(0)); // using current time as a seed for random numbers
// if we do not use a random seed the code will generate the same numbers over and over again

int number1 = (rand() % 6 + 1); // this gives a random number between 0 and 6
// as the remainder will be between 1 - 5 (modulus)
// rand() % n - using n number after modulus we get numbers between 1 to n-1
printf("%d", number1);
return 0;
}

MEMORY ADDRESS
memory - an array of bytes within RAM (like a street with a bunch of different houses)
memory block - a single unit (byte), within memory used to hold some value (like a person)
memory address  - address of where a memory block islocated (the house address)
in order to find certain data memory addresses are important
int main(){

    char a = 'X';
    char b = 'Y';
    char c = 'Z';
    // data type short uses 2 bytes of memory

    printf("%d bytes\n", sizeof(a));
    printf("%d bytes\n", sizeof(b));
    printf("%d bytes\n", sizeof(c));
    
    printf("%p\n", &a); 
    // format specifier for memory addresses is %p, and we need to put & before variable
    printf("%p\n", &b);
    printf("%p\n", &c);

// the memory addresses are in hexadecimals - 0-9 + A-F  
// here char a has memory address 0061FF1F   
return 0;
}