CBasics_notes.exe

FUNCTIONS

// functions are created outside of the main function seperately
// format - 
void function_name(variable){code}

// functioon  example
void birthday(){
    printf("Happy birthday to you!\n");
    printf("Happy birthday to you!\n");
    printf("Happy birthday dear person!\n");
    printf("Happy birthday to you!");
}

int main()
{
    // call to funtion is inside main function
    birthday();
    return 0;
}

ARGUMENTS AND PARAMETERS

void birthday(char name[], int age) // variables passed to function declaration are parameters
{
     /* functions cannot see inside other functions
    so our main function needs to make this function aware of the variables 
    through arguments
    */
    printf("Happy birthday to you dear %s!\n", name);
    printf("You are %d years old\n", age);
}

int main()
{

    char name[] = "Anisha";
    int age = 19;

    birthday(name, age); // variables passed inside call to function are arguments
    // the arguments and parameters do not have to have the same name 
    // imp is the order and data type
    return 0;
}

RETURN STATEMENT

double square(double x) // since this function is returning a double we put data type of function to the data type it is returniing
// unless the arguments are of different datatypes then we just precede function declaration by void
{
    double result = x * x;
    return result;
    // instead of defining a local variable we could also define this as 
    // return x * x
}

int main(){
    double x = square(3.14); // call to function 
    printf("%lf", x);

    return 0;
}

TERNARY OPERATORS
// shortcut to if/else when assigning/returning a value
// return (condition) ? value if true : value if false

int findMax(int x, int y)
{
    return (x > y) ? x : y; // return (condition) ? value if true : value if false
    // in  this example the ternery statement in terms of if else statement would mean 
    if x > y then return x else return y
}

int main(){

    int max = findMax(3, 4); // call to function 
    printf("%d", max);

    return 0;
}

FUNCTION PROTOTYPE

it is the fucntion declaration without a body before the main() function (using a void function)
then we later define the function after the main  function 
ensures that calls to a function are made with the correct arguments

- important notes
many c compilers do not check for parameter matching
missing arguments will  result in unexpected behaviour (but code will still run)
function prototype will cause compiler to flag an error if arguments are missing and helps in debugging
(also helps in debugging)


STRING FUNCTIONS

header file - #include <string.h>
some basic common string fucntions - 
1. strlwr(variable); - converts string to lowercase
2. strupr(variable); - converts string to uppercase
3. strcat(variable1, variable2); - appends string (variable2) at end of variable1
4. strncat(var1, var2, n); - appends given (n) amount of characters from string of var2 to var1
5. strcpy(var1, var2); - copies var2 to var1 (removes contents of var1)
6. strncpy(var1, var2, n); - copies given (n) amount of characters from string of var2 to var1 (overwrites first n characters of var1)

7. strset(var, 'n'); - sets all characters of var to given character
8. strnset(var, 'x', n); - sets first n characters of var to given character
9. strrev(var) - reverses a string

a. int result = strlen(var); - returns string length as int
b. int result = strcmp(var1, var2); - compares all characters of he 2 variables inside parathesis (returns 0 if they all match, if they r diff they will return a number beside 0)
c. int result = strncmp(var1, var2, n); - compares first n characters (from the left side) between the strings (0 if they mmatch)
d. int result = strcmpi(var1, var2); // does the exact same thing as strcmp but is  not case sensitive
e. int result = strncmp(var1, var2, n); // does the exact same thing as strncmp but is  not case sensitive

FOR LOOPS
- repeats a section of code a limited amount of times
 //for(conditions){code}
    for(int i = 1; i <= 10; i++) // we have to declare n index here inside paranthesis (i is short for index)
    // it is similar to for loops python using i (or any name)
    // iterations are interger numbers hence common practice is to use int i when describing oop conditions
    // (condition of where it starts; condition for how long it runs; contion for how i value changes after every loop)
    {
        printf("%d\n", i);
    }
** for(start condition; end condition; change of values)

WHILE LOOPS 
- repeats code possible umlimited times WHILE some conditions remain true
- it might also not execute at all depending on the conditions

char name[25];
printf("WWhat is your name?\n");
fgets(name, 25, stdin);
name[strlen(name) - 1] = '\0';

// while(condition){code excuted for when condition is true}
while(strlen(name) == 0) // while loop might not execute if condition is false from start
{
    printf("You did not enter your name!\n");
    printf("What is your name?\n");
    fgets(name, 25, stdin);
    name[strlen(name) - 1] = '\0';
};
printf("Hello %s", name);

DO WHILE LOOP 
- variation of a while loop 
- always executes a block of code once first and THEN checks the condition

int number = 0;
int sum = 0;

// since number is already set 0, a while loop will never excetue so 
// a do while loop needs to be used 
// format - do{code}while(condition);
do{
    printf("Enter a number above 0: \n");
    scanf("%d", &number);
    if (number > 0)
    {
        sum += number;
    }
}while(number > 0);
printf("sum: %d", sum);

NESTED LOOPS
- a loop inside another loop
int main(){
    
int rows; 
int columns;
char sym;

printf("Enter number of rows: ");
scanf("%d", &rows);

// since printf and scanf are used together (due to using scanf) next pfrintf execution is on a new line
printf("Enter number of columns: ");
scanf("%d", &columns); // the imput command has a newline buffer

// to get rid of the buffer we can just use a whitespace in front of %c in scanf
printf("Enter a symbol: ");
scanf(" %c", &sym); 

for(int i = 1; i <= rows; i++) // outer loop for rows and inner oop for columns
{
    for(int j = 1; j <= columns; j++){
        printf("%c", sym);
    }
    printf("\n");
    // for each row j will be printed and for a new row it will move to a newline
} 
 // first iteration of outer loop executes first and then then all the iterations of inner loop and so on */

    return 0;
}

BREAK VS CONTINUE
- continue skips rest of code and forces the next iteration of the loop
- break exits a loop/switch

e.g 
for(int i = 1; i <= 20; i ++)
    {
        if(i == 13){
            continue;
            // if reak was used here then the loop would be stopped at 12
        }
        printf("%d\n", i);
    }
return 0;

ARRAY
- data structure that can store many values of the same data type

// datatype variablbe_name[] = {multiple values seperated by a comma}
double prices[] = {5.0, 10.0, 15.0, 20.0};
char name[] = "Anisha"; // a string is just an array of characters

int numbers[3]; // we can also just set the number of items we are gonna assign the array and assign them later
numbers[0] = 1;
numbers[1] = 2;
numbers[2] = 3;
// we can also do both together double prices[4] = {5.0, 10.0, 15.0, 20.0};


// array elements are accessed by index numbers inside [] square brackets
printf("%.2lf", prices[3]);

ITERATING OVER AN ARRAY
double prices[] = {5.0, 10.0, 15.0, 20.0, 25.0, 30.0};

// it is better to set end condition using size of array
//cso that we do not need to update the conditions eerytime there is a cange to the array
printf("%d bytes\n", sizeof(prices)); 
// sizeof() operator tells us size of value assigned to the variable in bytes
// size of a single element is sizeof(variable)/sieof(variable[i])


for(int i = 0; i < sizeof(prices)/sizeof(prices[i]); i++){
    printf("%.1lf\n", prices[i]);
};