2. C programming

What does every C program have

Header file — function declarations and at least a main function (the entry point)

what line is at the top of every C file

The preprocessor directive, #include <stdio.h> , to include necessary header files.

What type does main have to return

the main function in C must return an int value (0 typically means success)

How do you write C comments

// single line
/* block comment */

Provide code to display hello world in C (create main too)

#include <stdio.h>

int main(){
	printf("Hello world\n");
	return 0;
}

what is the ‘short’ data type in C

a smaller integer (2 bits instead of 4)

what is unsigned and signed in C

unsigned means the value cannot be negative

variables are set to signed by default

what is the stack in C

memory used automatically for function calls and local variables

what is the heap in C

memory managed manually by the programmer for dynamically-allocated data

what is the symbol table

a compiler structure tracking global variables and function names

what is shadowing / masking in C

when a variable in an inner scope hides one with the same name in an outer scope

How is the heap used

allocated with malloc()

freed with free()

give an example of when malloc and free is used

int main() {
	int *num = malloc(sizeof(int));
	*num = 5;
	printf("%d\n", *num);
	free(num);
	return 0;
}

when is malloc needed

when you need memory while the program is running

free gives back the memory when you are done with it

what is an operand

the value or address an opcode / operator acts on

what is a unary operator

an operator that takes one operand e.g !x, ++i

what is a binary operator

one that takes two operands e.g. a + b

what is the modulo operator

%

what is the remainder operator

/

What does the operator & do

bitwise AND

what does the operator | do

bitwise OR

what does the operator ^ do

bitwise XOR

what does the operator ~ do?

bitwise NOT

what does the operator « do

bitwise left shift

5 « 1

moves the binary representation of 5 left by 1 place

what does the operator » do

bitwise right shift

5 » 1

moves the binary representation of 5 right by 1 place

what does putting & before variables do in c

gets the memory address of the variable

int x = 10;
printf("%p", &x);
// returns the address of the variable

what does putting * before variables do in c

it defines that the variable is a pointer.

it will store the address of a variable

int x = 10; 
int *p = &x;
printf("%d", *p);

what is a loop invariant

a condition that remains true throughout a loop’s execution

how does switch case work in C

switch () {
	case 1:
		//do something
		break;
	case 2:
		//do something
		break;
	default:
		//does something if no case match
}

how do you loop through a 2d array in c

int array[2][3];

for(i = 0; i< 2; i++) {
	for(j = 0; j < 3; j++) {
		printf("%d\n", array[i][j]);
	}
}

what does void mean in a function

that it returns no value

what is a library

a collection of pre-written compiled functions

How does C pass in its variables

pass by value

function parameters are copies; modifying them does not affect caller variables.

how do you modify a callers variable in C?

pass a pointer to it

void change(int *x){
	*x = 10;
}

int main() {
	int a = 5;
	change(&a);
}

what is a prototype in C

a function prototype is a declaration of a function before it is defined, so the compiler knows the name, return type and parameter types.

int add(int a, int b);

int main(){
	//...
}

how do you define a function in C

int add(int a, int b){
	return a + b;
}

replace int with void for no return type

In what order do 2d arrays use columns and rows

[row][column]

How is array data stored in memory

Contiguously

how do you initialise an array in C

int arr[] = {1, 2, 3, 4, 5};
// or 
int arr[5];

how do you read from an array in C

int x = arr[2];

how do you write to an array in c

arr[0] = 7;

how do you check if you are within the bounds of an array in c

if(index >= 0 && index < 5){
	arr[index] = value
}

What is a string made up of in C

A char array terminated by a null character (\0)

What is the string “hello” made up of in C

(h, e, l, l, o, \0)

how do you create a pointer to a string

char *s = "hello"

how do you create a modifiable copy of a string

char s[] = “hello”

how do you compare strings in C

strcmp(s1, s2);
/*
0 if equal
negative if s1 < s2
positive if s2 > s1
*/ 

how do you import strings in C

#include <string.h>

how do you get the length of a string in C

strlen(s)

how do you copy a string into a new char array in c

strcpy(dest, src)

how do you add strings together in c?

strcat(dest, src)

how do you search a string for a character

strchr(str, chr)
//returns pointer of first occurrence of search item 
//or returns null

how do you copy a certain amount of characters in a string in C

strncpy(dest, src, n)
// copies up to n characters

how do you print a string in C

char str[] = "hello";
printf("%s\n", str);

what is the format for printing an int in C

%d

what is the format for printing a char in C

%c

what is the format for printing a float in C

%f

what is a pointer

a variable that stores the memory address of another variables

what is indirection in pointers

accessing data through a reference to its location, rather than directly

what does dereferencing mean in C

accessing the value at the address a pointer holds

how do pointers work with different data types

pointers have different data types

int * points to ints

char * points to chars

how do you return an address of a variable

&variablename

what does a pointer need before being used

it needs to be initialised (normally to null)

how do you use &variable to let a function to use pass-by-reference

when defining the function, have pointers as parameters

void swap(int *a, int *b) {
    int temp = *a;
    *a = *b;
    *b = temp;
}

int main() {
    int x = 5;
    int y = 10;

    swap(&x, &y);
    return 0;
}

how do you read an input from the user

scanf("%d", &input)

remember the & for address of variable

how do you create a variable and create a pointer to the variable

int x = 7;
int *p = &x;

how do you make a swap function in C

void swap(int *a, int *b){
	int temp = *a;
	*a = *b;
	*b = temp;
}

when do you need to allocate memory in C

when you need data of a size only known at runtime

or data that outlives the function that created it

what does malloc(n) return

a pointer to n bytes of heap memory, or null if fails

what does sizeof() do in C and when do you use it

sizeof returns the size of the data type you need.

you use it when you are using malloc() to allocate the right amount of memory

int *p = malloc(sizeof(int));

what is a struct in C

a struct groups related variables of possibly different types under one name

structs let you build composite data types matching the structure of your problem (a person, point etc.)

what is a field / member in a struct

a variable inside a struct

what does . do in structs

gets a field through a struct variable

example:

p1.age = 20;

what does → do in structs

gets a field through a pointer to the struct

example:

struct Person *p = malloc(sizeof(struct Person));

p->age = 25;

what does → mean in structs

go to the struct that points to the pointer, and get the variable

what is a self-referential struct

a struct containing a pointer to its own type (for linked structures)