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CS 161Introduction to Programming
and Problem Solving
Chapter 6Programming Development
Environment
Herbert G. Mayer, PSUStatus 10/20/2014
Syllabus What is a Program? What is a Computer? Holding Data Programming Languages Machine Language Sample Compiler Linker Loader Debugger Quick Excursion to C++ While Loops in C++
Acknowledgments
Numerous graphs and pictures used here have been copied as-is from ECE 103 teaching material developed by professor Phillip Wong at PSU
What is a Program A computer program is a sequence of executable
machine instructions, reading information (input), computing new data, and generating output, according to the steps of an algorithm
An algorithm is a finite sequence of instructions, reading information (input), computing new data, and generating output
The two are almost synonymous, except that the program executes (AKA runs) on a computer, the algorithm is just an abstraction in our mind or written on paper
The algorithm coded in a programming language becomes your program
What is a Computer A computer is a physical device that can read input, compute,
and produce corresponding output It “understands” a small set of machine instructions, which it
can execute, one at a time (for a uni-processor) It is possible, but very tedious, to write a program in such
machine instructions An Assembler eases this tediousness by allowing users to
write abstract data and symbolic instructions, which the assembler then translates into machine code
A compiler (similar: an interpreter) reads higher-level programs and maps them into assembly code; or sometimes into machine code directly
What is a Computer
Main Memory(RAM, ROM)
Auxiliary Storage(e.g., disk drives)
Input(e.g., keyboard, mouse)
Output(e.g., monitor, printer)
Processor(CPU)
What is a Computer’s Processor?
Registers(fast storage)
Memory Interface
Instruction Decoder
To main memory
The ALU (Arithmetic Logic Unit) performs basic arithmetic, logic, and comparison operations.
ALU
Holding Data A computer holds a good amount of data in memory The size of such a memory (AKA primary storage) is
defined by the architecture’s address range E.g. on a 32-bit architecture, memory can be as large
as 232 different addressable units Often such units are bytes, i.e. 8-bit addressable,
contiguous units; other architectures use 60-bit words Large amounts of data are stored on secondary
storage devices, such as rotating disks or SSDs Access to data in memory is slow, about 10-100 times
slower than executing one instruction Access to data on disk is even 10,000s of times slower
Holding Data Getting data from memory into the processor
(usually a machine register) is called a load operation
Moving data from a register to memory is called a store operation
Such transport proceeds on a bus; the width of the bus and its speed are critical for the overall execution speed of the machine and thus of your programs
Programming Languages
Even writing assembly source code is highly tedious Since the 1960s, higher-level programming
languages have been developed Some of these are machine-independent; others
highly machine-dependent (AKA architecture-dependent)
A machine-independent language allows writing of source programs (code) that can be executed on different machines, provided a compiler is available on each
This is referred to a portability of source programs, quite a desirable property!
1969 to 1973 – C (Bell Labs initial development)
1978 – K&R C (Kernighan and Ritchie)
1989 – C89 (ANSI)
1990 – C90 (ISO)
1995 – C90 Normative Amendment 1 → "C95”
1999 – C99 (ISO)
2011 – C11 (ISO)
C Language Milestones
Machine Language Sample
600: A9 5A LDA #$5A ; Load accumulator with number 602: 18 CLC ; Clear carry flag603: 69 20 ADC #$20 ; Add $20 to accumulator
w/carry605: 8D 00 10 STA $1000 ; Store accumulator at $1000
Assembler translates an assembly program to machine languageAssembly language still requires a high level of programmer expertise
Compiler
Compiler is a special-purpose system program that reads source programs, written in the source language and translates them into machine language
Mapping into machine language (AKA object code) sometimes involves an intermediate step: Creating assembly source first, and then using the assembler to generate machine code
A compiler generally understands just one input language; exceptions are some C++ compilers that also read C source
Compilers emit error messages when certain violations are detected
Compiler
Source files contain the C++ program code .cpp extension (file is in text format); also .c
Header files can contain prototypes, macros, data type declarations, or code .h extension (file is in text format)
Object files contain intermediate compiled code .o -or- .obj extension
Executable files contain runnable binary code .out -or- .exe -or- no extension
Compiler
preprocessor → handles preprocessor directives and expands macro definitions
compiler → takes preprocessed source code files and translates them to intermediate code; for beginners it is convenient to view the other system programs as part of the compiler
assembler → takes intermediate code files and translates them to binary object code
linker → resolves references among the object files and the libraries. It puts all the parts together to create the final executable file
17
prog_1.c
prog_2.c
prog_3.cetc.
Source files
prog_1.o
prog_2.o
prog_3.oetc.
Object files
prog
Executablefile
stdio
stdlib
mathetc.
Library files
CompilerPreprocessor Linker
prog_1.h
prog_2.h
prog_3.hetc.
UserHeader files
stdio.h
stdlib.h
math.hetc.
LibraryHeader files
Assembler
Compiler
Linker
Often programs are composed of multiple source programs
For example, some projects are too large to have a single programmer develop all code in sequence
Also system function, such as input, output, heap acquisitions etc. are provided in the PDE, and do need to be coded by the programmer
All such elements are linked together into a single, executable object program
That is the work of the system’s linker For C on Unix the link step is frequently hidden, i.e.
not visible to the programmer
Loader
When a program has been linked, it is still not executable
Instead, it is just a binary file, residing on some disk, as an object file
To run such object code, it must be loaded into memory and be granted processor execution time
That is the purpose of the system laoder
20
Example: Vintage CPU (1975)
MOS 6502 Single core 8-bit data Memory
64 KB main Registers:
Accumulator (A) Index (X, Y) Processor Status (P) Stack Pointer (S) Program Counter (PC)
Speed: 1 to 2 MHz Process: 8 m # of transistors: ~3500
Die ShotPin-out
21
Example: Modern CPU (2013)
Intel i7-4770 Haswell Four cores 64-bit data Memory
4x256 KB L2 cache 8 MB L3 cache 32 GB main (3.2x107 KB) Registers:
8 32-bit 16 64-bit
Integrated GPU Speed: 3.4 GHz (3400 MHz) Process: 22 nm (0.022 m) # of transistors: ~1.4 billion
Die Shot
Package
Quick Excursion to C++
You now know C++ arrays The type of an array element may be any legal C++ type,
including array, in which case you declare multi-dimensional arrays
To manipulate arrays, generally you need loops Loops are syntactic constructs that allow the programmer
to do steps repetitively We also call this: iteratively Loops iterate over a so called iteration space C++ has while, for, and do loops Here we discuss while loops
While Loop in C++ Formally, there are no while statements, just expressions
in C++, we ignore this language politics for the moment A while statement consists of 3 parts:
1. Reserved keyword while
2. A parenthesized expression, interpreted as boolean
3. And 1 statement (formally an expression) Example:
while( i < MAX_SIZE ) {process_vector( i++ ):
} // end while The single statement may, of course, be a compound
statement
While Loop in C++ A while statement executes, as long as the boolean
expression in the pair of ( and ) yields true When the expression is false, the while statement ends,
and the operation after the while is executed next Usually, some operation in the body of the while –inside
the single statement, which may be a compound statement-- must ensure that the boolean condition is false eventually
Else you constructed an infinite loop Note that the boolean condition could be false at the
start, in which case the wile is empty, i.e. executed 0 times
While Loop in C++// declaration of some array#define TEN 10char digits[ TEN ];
// loop to initialize digits[]int i = 0;while ( i < TEN ) {
digits[ i ] = ‘0’ + i++;} //end while// no compound needed, but is a good habit