RC-midterm-review.md

VG101: Introduction to Computer and Programming

Midterm Review

Second Midterm

• 100-minute open-book paper exam
• Question types see sample exam on Canvas
• Easy

Header files

• Common libraries:

#include <stdio.h>   // For standard input and output.
#include <math.h>    // For basic mathematic operations like sqrt, sin, pow.
#include <stdlib.h>  // For random number generation and dynamic memory allocation.
#include <string.h>  // For efficient string manipulation.
#include <time.h>    // For recording program running time.

• Difference between <> and ""

main function

• main function is where a program starts executing.
• A program only contains one main function.
• main function is not callable for you. (No recursion for main function)
• Return type and return value for main should be int and 0 (non-zero return value is to indicate some errors)

int main() // Return type: a integer
{
	// Write your code here
	return 0; // Return value: 0
}

Variable

Variable name

• First character must be letter or _
• Followed by letter, number, or _
• Case sensitive. a and A are different variable names.

Variable type

• Basic variable types int, long long int, double, float, char
• Pointer types int *, double *, void *
• Constant const int, const int *, int const *
• Array int a[10]
• Structure type
• Question

// What is the variable type of a, b?
int * a, b;

Variable initialization

• Give value when declaration int a = 1, int * b = NULL
• Different variables split by ,
• Wrong: int a = b = 1 if b undeclared before.

Variable scope

• Start from declaration, end with the scope (block)
• Local variable, global variable, static local variable

Operations

Basic operations

• Assignment operator: =
• Arithmatic: +, -, *, /
• Remainder: %
• Increment, decreament: ++, --
• Shorthand assignment operators a += b
• (condition) ? expression1 : expression2
• Logic | operator | operation | | :----------: | :-------------: | | && | And | | || | Or | | ! | Not| | == | Equal to| | != | Not equal to|
• dereference, reference: * and &
• Question

// Right or wrong?
int ax, bx, cx;
1 = ax;
bx = cx = 1;

Other operations

• Data type conversion
  • Automatically data type conversion
  • Manually data type conversion
  • Question

// What's the value of each variable
int a = 1 + 1.5;
double b = 3 / 2;
double c = 3 / 2.0;
int d = a + b + c;
char e = 'a';
e = e + 1;
// What's the value of integerPi?
double pi = 3.1415926;
int integerPi = (int)pi; 

Control statements

• if, switch, while, for
• continue, break
• Mind the place of ;
• Block {}: enclose multiple statesments
• Block {} can be omitted if it only enclose one statement.
• Again, Indent is important and useful!
  • In midterm2, TA hand grade your code. No indent -> messy -> grading mistakes.

Function

• Syntax:

int add(int a, int b)   // returnType functionName (parameterType parameter, ...)
{						// block enclose function content
	return (a + b);		// return value (must consistent with returnType)
}

• Parameter passed by value
• Same variable name can be used in different function (they do not share value)
• If the inside variable share the same name with the outside variable, it will block the outside one
• Use void function if function return nothing.
• Use void parameter if function needs no input parameters. (can be omitted)

void helloWorld(void)			// No input parameter, no return value. void helloWorld() is also okay
{
	printf("Hello world\n"); 	// Only do something.
}

I/O

• Include <stdio.h>
• Output function: printf
• Input function: scanf
• File output function: fprintf
• File input function: fscanf
• File pointer FILE *

Arrays

• An ordered collection of data values of the same type.
• Size must be a constant number.

Declaration and initialization

• Declare an array: type, name, size.
• Macro define: #define MAX_SIZE 100
• Ways of initialization

int zeros[20] = {0}; 					// All elements initialized as 0
int notAllZero[20] = {1}; 				// Only the first one will be 1, other will be 0
int numbers[5] = {1, 2, 3, 4, 5};
int numbers[] = {1, 2, 3, 4, 5}; 		// Equivalent to previous
char str[4] = {'a', 'b', 'c', '\0'}; 	// Define a string, '\0' is ASCII 0
int numbers[5];
for (int i=0; i<5; i++)
	numbers[i] = i+1;

Element accessing

• Index starts with 0.
• Can use integer variable/expression to as array index
• Be careful: array out of bounds!

Two-dimensional Array

• An array whose elements are arrays.
• Use A[i][j] to access elements.
• Row first, column second.
• Stored as one dimensional array in memory.
• Address issue is more complicated.
• Higher-dimensioanl array has same property.

C-style string

• An character array end with '\0' (0 in ASCII)
• Always remember to keep a place for \0 (it is also a char)
• Difference between char array and C-style string
• Common string function (<string.h>)
  • fgets
  • strlen
  • stpcpy, strcat, strcmp
  • strchr, strstr
  • atoi, atof, atol

Pointer

Declaration and Assignment

• Pointer declaration int * px
• Pointer assignment px = &x
• NULL pointer
• void * pointer

Array with Pointer

• Array name is a pointer!
• array[3] is equal to *(array + 3)
• A two dimension array is essentially an array of pointer.
• The type of a constant C-string "Hello World!" is essentially a const char*
• Question

// Which element will be printed?
int a[5][5];
printf("%d\n", *(a+10));

Advanced pointer structures

• pointer to pointer int ** pt
• array of pointers int* pt[10]

Dynamic Memory Allocation

• #include <stdlib.h>
• malloc() and free()
• Use sizeof() to calculate size.

int *arr = (int *) malloc(10*sizeof(int));		// allocate an piece of memory 
												// with the size of 10 ints
free(arr);										// free the memory

• Life cycles of allocated memory: start with malloc(), end with free()
• You must free all the memory you allocate.

Structure

• Assemble a package of variables into a structure.
• Two ways to define strctures (they are equivalent):

struct Student
{
	char name[100];
	int studentID[12];
	int midtermScore;
};
struct Student t;

typedef struct
{
	char name[100];
	int studentID[12];
	int midtermScore;
} Student;
Student t;

• Access member data
  • use . to visit member data. t.midtermScore
  • use -> if using pointer. pt->midtermScore

Tips

• Arrogance instead of ignorance is your enemy. (Especially in an easy exam)
• Don't forget to add ;
• Do intend your code