C Lecture

A little history:
 1970’s
 Unix
 C, from BCPL (Thompson and Ritchie)
 C programming Language
 Widely used like the others: Fortran, Pascal
 Main form of language for system programming
 Available on any machine with C compiler and
library

Some Characteristics:
 Scope:
 Intended:

HPC, OS, general programming

Typically, long developing cycle

very platform dependent
 Not intended: web, scripting, data processing
 Features:
 Close interaction with system

Standard library (user-level only),

no other fancy stuff: networking, memory, graphics
 Extensive use of pointers
 Procedure (OOB) programming, strictly pass by value

Sample 1:
/* Hello World! */
#include <stdio.h>
int main()
{
printf(“Hello World!n”);
return 0;
}

Walk through:
 C program: hello.c
 emacs, vi, vim, pico, joe …
 But text editors only. No word processor
 Preprocessing: hello.s, assembly code
 cc -S hello.c
 Compilation: hello.o, a binary file
 cc -c hello.s
 Linking: a.out or hello, an executable file
 cc hello.o
 cc -o hello hello.o
 Loading (dynamical linking) and execution: ./hello
 ./a.out
 ./hello

Programming (Editing)
 C program: hello.c
 emacs, vi, vim, pico, joe …
 But text editors only. No word processor

Compile:
 Preprocessing: hello.s, assembly code
 cc -S hello.c
 Can you take a look at hello.s and compare to hello.c?
 Compilation: hello.o, a binary file
 cc -c hello.s
 Do you know how to take a look at hello.o?
 Linking: a.out or hello, an executable file
 cc hello.o
 cc -o hello hello.o
 Want to look at the executable, hello?

Run:
 Loading (dynamical linking) and execute: ./hello
 ./a.out
 ./hello
 What you do with java programs?
 What computer does to run your program?

Sample 1 Dissection:
 What it has?
 A function definition: main
 A line of comment
 A line of preprocessor directive
 An output statement
 A return clause
 What it does?
 Ask the computer to say hello to the world.
 What it does not do?
 It seems not computing!!
 No real work

not taking input

does not change any value

Sample 2:
#include <stdio.h>
#define MAGIC 10
int main(void)
{
int i, fact, quotient;
while (i++ < 3) {
printf(”Guess a factor of MAGIC larger than 1: ");
scanf("%d”, &fact);
quotient = MAGIC % fact;
if (0 == quotient)
printf(”You got it!n”);
else
printf(”Sorry, You missed it!n”);
}
return 0;
}

Sample 2 Dissection:
 What more it has?
 Macro definition
 Variable declaration
 Operations represented by operators
 Conditional computation
 Input Processing
 Loops: three chances

Syntax Dissection:
 What is syntax?
 m-w.com:

the way in which linguistic elements (as words) are put together
to form constituents (as phrases or clauses)
 How to put your C elements together into a program?
 Variable declaration,
 Identifier: case, keywords, style
 datatype specification

char, short, int, long, float, double
 Operators:
 +, -, *, /, %, ++, --; >, <, ==, ; &, |, …
 Priority and Precedence
 Associativity

More Syntax Dissection:
 Preprocessor directive
 macro
 header file inclusion
 Loop constructs
 for, while, do-while, break, continue, label--go;
 Conditional statements
 If, else, else if, switch, break
 Function definition
 return type, parameter definition, parameter passing
 Standard library and function calls
 Take home practice:
 Walk through the following steps with sample 2

preprocessing, compilation, linking, loading/execute

Modify and repeat once more if you can

C Lecture

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