rev='made'/> name='keywords'/> name='author'/> ANURANAN: Introduction to C

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Introduction to C


Introduction to  C
C History
Developed by Dennis Ritchie at AT&T, early 70s, for DEC PDP-11
Unix written in, closely associated with, C
Family of languages:
BCPL, Martin Richards
B (typeless), Ken Thompson, 1970
C, Dennis Ritchie, Bell Labs, early 70s
C++, Bjarne Stroustrup, Bell Labs, 80s
Java, James Gosling Sun, 1995
C#, Microsoft, recently
C++, Java, C# conserve (much) C syntax

First C Program
Basics of a Typical C Program Development Environment
          Phases of C Programs:
1.       Edit
2.       Preprocess
3.       Compile
4.       Link
5.       Load
6.       Execute
C Compilers, Linkers, Loaders
Some Key Terms
Source Program
printable/Readable Program file
Object Program
nonprintable machine readable file
Executable Program
nonprintable executable code
Syntax errors
reported by the compiler
Linker errors
reported by the linker
Execution/Run-time errors
reported by the operating system
Compile a program
In  Windows Environment (using Visual C++ 6):
Compile a program
cl is used to compile and link a program
cl first.c
Run a program
first.exe
In Linux Environment:
Compile a program
gcc is used to compile and link a program
gcc first.c –o first.o
Run a program
./first.out
Integrated Development Environments
An integrated development environment (IDE) is a software package that makes it possible to edit, compile, link, execute, and debug a program without leaving the environment.
Example: Visual C++ 6, Dev CPP, Eclipse
You can find a document file in course website (named “Visual C++ 6.ppt” under resources folder) where it is described how to create a simple program, how to compile, build and run it.
The General Form of a Simple Program
Simple C programs have the form
                directives
 
                int main(void)
                {
                  statements
                }
The General Form of a Simple Program
C uses { and } in much the same way that some other languages use words like begin and end.
Even the simplest C programs rely on three key language features:
Directives
Functions
Statements
Directives
Before a C program is compiled, it is first edited by a preprocessor.
Commands intended for the preprocessor are called directives.
Example:
                #include <stdio.h>
<stdio.h> is a header containing information about C’s standard I/O library.
Directives
Directives always begin with a # character.
By default, directives are one line long; there’s no semicolon or other special marker at the end.
Functions
A function is a series of statements that have been grouped together and given a name.
Library functions are provided as part of the C implementation.
A function that computes a value uses a return statement to specify what value it “returns”:
                return x + 1;
The main Function
The main function is mandatory.
main is special: it gets called automatically when the program is executed.
main returns a status code; the value 0 indicates normal program termination.
If there’s no return statement at the end of the main function, many compilers will produce a warning message.
Statements
A statement is a command to be executed when the program runs.
first.c uses only two kinds of statements. One is the return statement; the other is the print statement.
Asking a function to perform its assigned task is known as calling the function.
first.c calls printf to display a string:
                printf(“Welcome to CSE102.\n");
Statements
C requires that each statement end with a semicolon.
There’s one exception: the compound statement.
Directives are normally one line long, and they don’t end with a semicolon.
Printing Strings
When the printf function displays a string literal—characters enclosed in double quotation marks—it doesn’t show the quotation marks.
To make printf advance one line, include \n (the new-line character) in the string to be printed.

Printing Strings
The statement
                printf(“Hello World\n");
                could be replaced by two calls of printf:
                printf(“Hello ");
                printf(“World\n");
The new-line character can appear more than once in a string literal:
                printf(“Hello\nWOrld\n");
Variables and Assignment
Most programs need to a way to store data temporarily during program execution.
These storage locations are called variables.
Types
Every variable must have a type.
C has a wide variety of types, including int and float.
A variable of type int (short for integer) can store a whole number such as 0, 1, 392, or –2553.
The largest int value is typically 2,147,483,647 but can be as small as 32,767.
Types
A variable of type float (short for floating-point) can store much larger numbers than an int variable.
Also, a float variable can store numbers with digits after the decimal point, like 379.125.
Drawbacks of float variables:
Slower arithmetic
Approximate nature of float values
Declarations
Variables must be declared before they are used.
Variables can be declared one at a time:
                int height;
                float profit;
Alternatively, several can be declared at the same time:
                int height, length, width, volume;
                float profit, loss;
Declarations
When main contains declarations, these must precede statements:
                int main(void)
                {
                  declarations
                  statements
                }
Assignment
A variable can be given a value by means of assignment:
                height = 8;
                The number 8 is said to be a constant.
Before a variable can be assigned a value—or used in any other way—it must first be declared.
Assignment
A constant assigned to a float variable usually contains a decimal point:
                profit = 2150.48;
It’s best to append the letter f to a floating-point constant if it is assigned to a float variable:
                profit = 2150.48f;
                Failing to include the f may cause a warning from the compiler.
Assignment
An int variable is normally assigned a value of type int, and a float variable is normally assigned a value of type float.
Mixing types (such as assigning an int value to a float variable or assigning a float value to an int variable) is possible but not always safe.
Assignment
Once a variable has been assigned a value, it can be used to help compute the value of another variable:
                height = 8;
                length = 12;
                width = 10;
                volume = height * length * width;
                  /* volume is now 960 */
The right side of an assignment can be a formula (or expression, in C terminology) involving constants, variables, and operators.
Printing the Value of a Variable
printf can be used to display the current value of a variable.
To write the message
                Height: h
                where h is the current value of the height variable, we’d use the following call of printf:
                printf("Height: %d\n", height);
%d is a placeholder indicating where the value of height is to be filled in.
Printing the Value of a Variable
%d works only for int variables; to print a float variable, use %f instead.
By default, %f displays a number with six digits after the decimal point.
To force %f to display p digits after the decimal point, put .p between % and f.
To print the line
                Profit: $2150.48
                use the following call of printf:
                printf("Profit: $%.2f\n", profit);
Printing the Value of a Variable
There’s no limit to the number of variables that can be printed by a single call of printf:
                printf("Height: %d  Length: %d\n", height, length);
PROBLEM SOLVING
Very Important
Problem Solving Methodology (must read)
Example 1          
1. Problem statement
   Compute the straight line
   distance between two points in a plane
2. Input/output description
            See C Programming    page   plz.
3. Hand example
See C Programming    page   plz.
4. Algorithm development and coding
a. Generalize the hand solution and list/outline the necessary operations step-by-step
1)      Give specific values for point1 (x1, y1) and point2 (x2, y2)
2)      Compute side1=x2-x1 and side2=y2-y1
3)      Compute
4)      Print distance
b. Convert the above outlined solution to a program using any language you want (see next slide for C imp.)
Example 1           (cont’d)
Example 1           (cont’d)
5. Testing
After compiling your program, run it and see if it gives the correct result.
Your program should print out
                                The distance between two points is 3.61
If not, what will you do?
               

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