3 What make us programmers? People who write programs are called programmers.
4 What is a Program? A sequence of statements that instruct a computer in how to solve a problem is called a program. Statment 1 Statment 2 Statment 3...
5 What is Programming? It is the process of planning a sequence of steps (called instructions) for a computer to follow. STEP 1 STEP 2 STEP 3... The act of designing, writing and maintaining a program is called programming.
6 What kinds of statements do computers understand? A computer only understands machine language statements. A machine language statement is a sequence of ones and zeros that cause the computer to perform a particular action, such as add, subtract, multiply, … e.g,, Add two numbers 100000010
7 Machine Language (ML) ML statements are stored in a computer’s memory, which is a sequence of switches. For convenience of representation, an “on” switch is represented by 1, and an “off” switch is represented by 0. ML thus appears to be binary (base-2): e.g,Add two numbers100000010
8 Lets see more about Computers Chapter_01_2_Computer_Organization.ppt
9 Back to Programming Chapter_01_1_Programming_and_Languages.ppt
10 Machine Language is not portable runs only on specific type of computer is made up of binary-coded instructions (strings of 0s and 1s) is the language that can be directly used by the computer
11 Early Computers... required a programmer to write in machine language (ML)... –Easy to make mistakes! –Such mistakes are hard to find! –Not portable -- only runs on one kind of machine! (CPU) Programming was very difficult!
12 A Bright Idea Devise a set of abbreviations (mnemonics) corresponding to the ML statements, plus a program to translate them into ML. The abbreviations are an assembly language, and the program to translate them into machine language is called an assembler. Assembler 100000010ADD
13 Assembly Languages Allowed a programmer to use mnemonics, which were more natural than binary numbers. +Much easier to write programs +Much easier to read programs +Much easier to find and fix mistakes –Still not portable to different machines
14 Assembly Language (middle level) a more or less human readable version of machine language words, abbreviations, letters and numbers replace 0s and 1s easily translated from human readable to machine executable code like machine code, not portable (hardware dependent)
15 Devise a set of statements that are close to human language (if, while, do,...), plus a program to translate them into ML. The set of statements is called a high level language (HLL) and the program to translate them into machine language is called a compiler. High Level Languages
16 HLL Compilers Where an assembler translates one mnemonic into one ML statement, a HLL compiler translates one HLL statement into multiple ML statements. Compiler 10101100 00000000 00101110 00000000 00101110 00000000 z = x + y;
17 HLLs High level languages (like C++) are +Much easier to write programs +Much easier to read programs +Much easier to find and fix mistakes +Portable from one machine to another (so long as they keep to the language standard).
18 High Level Languages are portable user writes program in language similar to natural language examples -- FORTRAN, COBOL, Pascal, Ada, Modula-2, C++, Java most are standardized by ISO/ANSI to provide an official description of the language
20 Interpreters Interpreters - another way to translate HLL to machine language or object code –interpretation (from source to object code) is not a separate user step –translation is “on-line,” i.e. at run time Interpreter High Level Language machine language
21 Compilers vs. Assemblers vs. Interpreters Compilers and Assemblers –translation is a separate user step –translation is “off-line,” i.e. not at run time Interpreters - another way to translate source to object code –interpretation is not a separate user step –translation is “on-line,” i.e. at run time Assembler Assembly Language Machine Language Compiler, or Interpreter High Level Language Machine Language
22 Compilers vs. Interpreters Compiled programs execute faster than interpreted programs Interpreters are popular in program development environments in which programs are recompiled frequently as new features are added and errors are corrected. Once a program is developed, a compiled version can be produced to run most efficiently.
23 Where we use Interpreters? Java virtual machine
24 Objectives in Programming A program should solve a problem: +correctly (it actually solves the problem) +efficiently (without wasting time or space) +readably (understandable by another person) +in a user-friendly fashion (in a way that is easy for its user to use).
25 Running a Program Program Computer Processing Data Data input (input for the program) Data Output (Output of the program)
26 Running a Program Data Output ( output for the program) Program Data Input (input for the program) Computer, Processing Data
27 Summary There are “levels” to computer languages: –ML consists of “low” level binary statements, that is hard to read, write, and not portable. –Assembly uses “medium” level mnemonics: easier to read/write, but not portable. –C++ is a “high” level language that is even easier to read/write, and portable.