Ecse 202 midterm prep

Warning with low language

-no range checking (checking if the value is within th bounds of the array) -limited type safety at compile time (type checking checks if the type used can be used ex. using modulo % will only work if theres two integers) -no type checking at run time

Write a program to calculate the sum of digits from 0 to 5

#include <stdio.h> int main(){ int i,sum=0; for (i=0; i=<5; i++) sum=sum+i ;// i++= i+1 print("The sum of digits from 0 to 5 is %d.\n",sum); }

Tips on how to handle it with care to avoid problems :

- Always run a debugger like gdb -never run as root (when youre doing it as admin) -never test code on Athena servers (MIT academic computing environment)

IDE : all in one solution popular ones? what are they? very convenient fro what ?

- Eclipse -Microsoft Visual C++ -KDevelo, XCode -Integrated editor with compiler, debugger - very convenientfor larger programs

CV related languages

- Most recent derivative : C++, Objective C, C# Influenced : Javal Perl Python

what is gcc what is gc extension (hint u use it in cmd)

- compiler his extension is -o

Conditional preprocessor macros #if #ifdef #ifndef #else #elif #endif can control which lines are compiled

-evaluated before code itself is compiled so conditions must be preprocessor defines or literals -used in header iles to ensure declarations happen only once

Strings : strings stored as character array - null terminated in C (write what it means )

-last character in array is '\0' , not written explicitely in string literals (output to the printer as written)

there exists more complicated form of gcc

-multiple source files -auxiliary directories -optimization linking

family of data types in C

-numeric (int, float, double) -character (char) -user defined (struct, union )

types of operators : 1.unary operators 2. binary operators 3.ternary operators

1. operate on a single operand ex. -, ++, -- , ! (not ) 2.operate on 2 operands (+,-,*,/) 3.operates on 3 operands (?, : ex.a ? b : c)

Examples 1. #pragma 2. #error, #warning 3. #undef msg

1. preprocessor directive it's basically compiler directives that are not default 2.trigger a costum compiler error/warning 3. remove the definition of msg at compile time

suppose x and v are variables Binary arithmetic: x+y, x-y, x*y, x/y, x%y Simple statement : y= x+3*x/ (y-4); (; ends statement not new line) What do these mean : 1. x+=y 2. x-=y 3.x*= y 4. x/=y 5.x%=y

1. x+y=x 2. x-y=x 3. x*y=x 4.x/y=x 5.x%y=x

Other important header files

<stlib.h>, <ctype.h>, <math.h> , <stdlib.h> , <string.h> , <time.h>

Def: compiler

A program that translates high level code (e.g. C) into that native instructions of the machine on which the code is executed.The output is usually in the form of assembly language, a symbolic representation of the machine's instruction set.

what is a return value?

A single value returned to caller when function exists

Assembly language if branch=0 base on last ALU instruction performed

BREQ

Def: linking

Combines object code with library and system code to produced a program that can be directly executed by hardware (the case with C) or interpreted by software (ex java virtual machine)

Assembly language : ADD instruction has 2 forms. Form 1: ADD destination, source 1, source 2

Computes sum of values in location source 1 and 2 result to destination

Assembly language: LD (load) type 1/ LD : destination, source give definition

Copies the data at memory location source to memory location destination

Assembly language: LD (load) type 2 : LDI : destination value

Copies values a numeric argument embedded directly in the instruction to destination

In a basic computer what is the data memory linked to? (2) for two headed

Counter program(2), controller(2),input\output(2),to ALU

In a basic computer , what is the input\output linked to?

Data memory(2)

In a basic computer, What is the program counter linked to? Put (2) if it's a 2-headed arrow

Data memory(2), controller(2),program memory(2), ALU(2)

In a basic computer, what is the controller linked to?(2) for 2-headed arrows

Data memory(2),from program memory, counter program(2),ALU(2)

C History :who invented it , where did he work (electrical eyyy) ,when and where did he do it? on what computer?

Dennis Ritchie - AT&T Bell , Laboratories 1972, 16-bit DEC PDP-11

How does source code get translated into executable code? (Schema)

Source code-->compiler+Assembly-->object code(+other object code & libraries)-->linker-->executable

what is a datatype?

The datatype of an object in memory determines the set of values it can have and what operations that can be performed on it C is weakly typed language it allows implicit conversions (type conversions by the compiler) as well as forced (potentially dangerous) casting

what is an expression

a combination of values , operators, variables and functions

const char msg[]

a constant array of characters

QUESTION : When it's written : the gcc option Dname=value sets a preprocessor define that can be used

does this mean write that on the cmd when looking for our file

return 0 ;

exits the function, returnin value 0 to caller we put this because the main function signature requires it in C , it's the exit code for the program

Why is C widely used today

extends to newer system architecture low level access (works closely with the processor's instruction) efficiency/performance

What does C feature?

fils comme pute mange ses endives (Few keyworks, Compiles to native code, Pointers- memory,arrays, Macro preprocessor, Structure, unions, compound data type , External Standard Library - I/O , other facilities

How do i insert parentheses to get z= 4.0

float z = (x+3*x)/(y-4)

What are declaration of functions called

function prototype

to enable compiler warning use wall where ?

gcc -wall filename.c -o filename.o

How would you write a function type factorial which returns an integer and has one argument

int factorial (int); int factorial (int n)

Two argument form of main() : access command-line arguments

int main (int argc, char** argv);

write the code to store the string in a variable before printing

int main (void ) { const char msg[] = "hello 6087 students" ; puts (msg); return 0; }

Declaring variables : we must declare variables before use ; write the way we should do it for an integer number and a fractional number with the variable x

int x; float x;

const keyword

qualifies variable as constant

#define can also take arguments and be treated like a function ex. #define add3(x,y,z) ((x)+(y)+(z)) compiler performs inline remplacements which means that it's not suitable for

recursion

What's the general form of declaring a function?

return type function name (arg1, arg2...)

naming rules for variables

-they can contain letters, digits and_ -name should start with letter -keywords cannot be used as variables (ex. for while etc) -variable names are case sensitive (theres a pop quix slide 9 ppt 2 if u wanna practice)

int x=0 , y=0 y =x+2 what are the variables, the expression and the operator

-x,y are variables -y=x+2 is the expression - + is the operator

Structure of a C file

/*Begin with comments about filecontents*/ Insert#includestatementsandpreprocessordefinitions Functionprototypesandvariabledeclarations Definemain()function{Functionbody} Defineotherfunction{Functionbody}...

Special characters specified in C using \ (escape character) what do these mean ? 1. \\ 2. \' 3.\" 4. \b 5. \t 6. \r 7. \n 8.\ooo 9. \xhh

1. backlash 2.apostrophe 3. quotation mark 4.backspace 5.tab 6.carriage return (cursor at the beginning of the line) 7.line feed (start a new line) 8. Ascii character translates letters into binary code theres 127 of them

Initializing values : uninitialized variable assumes a default value 1. variables initialized via assignment operator 2.can also initialize a declaration 3.can declare/initialize multiple variables at once Give examples for each

1. int n n=3; 2. float phi=1.4793749; 3. int a, b ,c=2, d=4;

Console input/ output: stdout, stdin: console output and input streams What do these mean? 1.puts(string) 2.putchar(char) 3.char = getchar() 4.string = (get(string))

1.print string to stdout 2. print character to stdout 3. return the character from stdin 4. read the line from stdin into string

Order of operations : say the evaluation direction for each of these signs 1. +, - (sign) 2. *, /, % 3. + , - 4. =, +=, -=, *= , /= , %= Use parentheses to override order of evaluation

1.right-left 2. left to right 3. left- right 4. right to left

Numeric data type write the different data types in their signed and unsigned counterparts (the unsigned has double the range , they only differ in arithmetic expressions) 1. short 2. default 2. long 4. float 5. double 6. char

1.short int x; short y; - unsigned short int x, unsigned short y; 2. int x ; - unsigned int x 3. long x - unsigned long x 4. float x - N/A 5. double x - N/A 6. char x,signed char x - unsigned char x;

1972 :? 1978:? 1989:? 1990: ? 1999: ? 2007: ?

1972 : Cinvented 1978 : C programming languge 1989: C89 standard (known as ANSI C or standard C) 1990: C99 Standard -mostly backward compatible -not completely implemented in many computers -2007 : work on new C standard C1 X announce Inn this course : ANSI/ISO C 9C89-C90)

Def:input/output

Allows external access to data memory

Assembly language : BR (branch) #instructions to skip instruction : which one is unconditional vranch

BR

Assembly language which one is branch if >0 based on the last ALU instruction performed Branch is an instruction that makes the program execute a different instruction sequence and deviate from its default path

BRGT

Assembly language which on is branch if <0 base on last ALU instruction performed

BRLT

What is C used for

C is used for MODE Microcontrollers : airplanes and automobiles Osed , like Linux DSP processors : digital audio and TV systems E : embedded processors : phones, portable, electronics etc.

Advantage of a low level language?

Faster code

Assembly language: ADD instruction type 2 : ADI def

Like add but second argument is value embedded in instruction

C lacks

PORGE (Like the purge ) Polymorphism , Object-oriented programming, Range-checking, Garbage collection, Exceptions

Def: ALU, Arithmetic and logical unit *has a minimal instruction set{ADD,COMP(1's complement),AND,OR,SHL(shift left),SHR(shift right),ASR(arithmetic shift right),ROL (rotate left) and ROR (rotate righr)

Performs arithmetic and logical operations on entities stored in data memory

In a basic computer, what is the ALU linked to?2 for two headed

Program counter(2),controller(2),from data memory,to program counter

What is source code (written in a text editor) also referred to as?

Raw TEXT or ASCII

Def: Program counter

Register containing the adress in program memory of the next instruction to execute.The new Program counter value is calculated as a by product of the current instruction.

Controller

Sequences data with ALU to perform machine instructions.Sequences groups of instructions to compute programs.

Comments

Simple comment /*this is a simple comment*/ can span multiple lines -can appear almost anywhere

In a basic computer, what is the program memory linked to?(2) for 2-headed arrows

To controller,from program counter

Def : compilation

Translates code from high level code into an intermediate representation (assembly language) which ultimately is stored as object code and stored as files of binary data

QUESTION : included files must be on include path -Idirectory with gcc : specify additional include directories -standard include directories assumed by default

What are thses standard directories assumed by default?

Def : data memory

Where data associated with a program is stored. Most machines can adress memory in chunks of 8-bits(byte),16-bits(short word),32-bits(long word),64 bits(long long word)

Def: Program memory

Where the program is stored in machine code.A compiler translates high level code into a set of simple instructions that are interpreted by the hardware.

you need to be aware of how the code you write impacts performance (write example in a) ) you need to be aware of tradeoffs that can be made (ex. b)

a) size , speed power b)hardware vs software, speed vs battery life, cost of design vs security of code

what is a variable

as named link/reference to a value stored in the system's memory or an expression that can be evaluated

Useful commands in gdb (debugger)

break (line number) : create breakpoint at specified line break (file: line number) : create breakpointat specified line in file) c : continue execution run : run program next : execute next line step : execute next line or step into function quit : quit gdb print (expression) : print current value of the specified expression help (command) : in program help

performance depends on

compiler ( efficiency translation of the code), the characteristic of the hardware, characteristic of the algorithm (computational complexity)

what is the char data type in C

corresponds to a signed (can be positive or negative ) 8 bit integer [-128, 127], it happens that this is a convenient representation for the ASCII character code

char

data type representing a single character written in quotes 'a', '3' , 'n'

what is embedded in gcc?

debugging info and disable optimization

Preprocessor macros begin with # character #include <stdio.h> #define mds "hello, 6087 students" what does it do

defines msg as "hello 6087 students" throughout source file

main () entry point for C program what is the simplest version of main : no inputs, outputs0 when succesful and nonzero to signal some error

int main(void)

write code that puts "hello 6087 students" on the console

int main(void) { puts ("Hello 6087 students"); } return 0 ;

What does the #include in C mean

it calls a header file which contains functions, constants and other declarations

What are arguments?

local variables , values passed from caller caller is basically the main function at the beginning ex. void (calculate) int (counter= 0) add (counter, 5) calculate is the caller

what does void signify?

no return value/arguments

what is puts() :

output text to console window (stdout) and end the line (stdout is a pointer to a file which represents the default output device for the application

string literal

output to the screen or printer as written written surrounded by double quotes

<stdio.h> what is it

standard I/O (input/output) functions for consoles, files

what does int factorial (int n ) mean?

the function takes int and returns int

operators

they specify how an object can be manipulated (ex. numeric vs string operations

Evaluate the statement : float z = x+3*x/(y-4) x= 2.0 y=6.0

z=5.0