This course has three parts. Elements of C programming. Arithmatic and Error analysis. Some algorithms and their implementation

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2 This course has three parts Elements of C programming. Arithmatic and Error analysis. Some algorithms and their implementation 2

3 There are three steps involved in converting your idea of what is to be done to a working program Creating a source code in the form of the text file acceptable to the compiler. Invoking the compiler to process the source code and produce an object file. Linking all the object files and libraries to produce an executable

4 Source Code Compiler Object Code Other object codes Linker Function Libraries Executable

5 The tradition is to use the C source code with an extension.c For example myfile.c The compilation and linking steps are usually combined into one by the compiler. Let us look at an example of a C program that uses a library and another function.

6 A Sample code sample.c #include <math.h> #include <stdio.h> main() float x,y; while(x++<10.0) y=sqrt(x); printf("%f\n",y); } printit();

7 Create print.c printit() printf ("The program is Over"); }

8 To compile these programs we could type cc -c sample.c and cc -c print.c separately. This commands will create sample.o and print.o files. We can create the executable by typing the command. cc sample.o print.o -lm -o a.out

9 In this linking command we have put together the two files and also included the math library file m.a We can now execute the program by typing a.out. You could see variations of these commands and programs to figure out why we need the math.h file and why we need to include -lm in the linker etc.

10 The anatomy of a program Compiler preprocessor commands main function name() variable declaration code } sub-function-name (arguments) argument declarations variable declarations code }

11 The standard C compiler has four filters. The first one is known as the preprocessor. This part handles the inclusion of files mentioned using the #include command, definition of constants, macro definition etc. The second filter checks the language statements, generates a symbol table and reports any errors found. The third part generates the code and a fourth filter optimises the code for better performance.

12 Variable declarations C language require that all variables are declared before they can be used. Here we declare the variable with its class name and the data type. The variable declarations can have the following form, [class] [type] [name][ = initial value]. The "initial value" is not a necessary quantity. For example we can declare the real variable "trial" using "auto float trial" or "auto float trail = 0.0". In the latter we also assign the variable a value "0.0".

13 Class In both the above statements given in the previous page we have assigned the [class] as auto. In fact this is the default class and not necessary to be mentioned in the declaration. An auto variable is local to the function within which it is declared. Every time the function is entered we need to assign a value to it before it is used.

14 External is another class that is possible. An external variable is global to the program. It should be defined outside the function boundary. A function that uses it should declare it as extern. The first declaration creates the storage and the subsequent declarations does not create storage, but just tells the compiler that the reference to this variable should be resolved by the linker. An example of a program that used the real variables x and y as external is given below.

15 float x,y; main() } Function() extern float x,y;... } Here in order to use the variables x and y the function declares it as extern. External variables can be used even by functions in different files as long as the names match.

16 Static variables are initialized only once by the function. The static data is assigned the initial value only on the first time the function is entered and is not re-initialized every time the function is entered.

17 #include<stdio.h> #include<math.h> main() float x, y, z; for (x=0.0;x<=10.0;x++) z=2.0/3.0; y=cube (x); printf ("%f %f \n",pow(x,2),y); } } cube(x) float x, y; y=x*x*x; return (y); } Sample program Header Files Variable Declaration Constants Assignment Statements

18 Data Types int float char short long un signed double 32 bit

There are three steps involved in converting your idea of what is to be done to a working program

There are three steps involved in converting your idea of what is to be done to a working program PROGRAMMING Before we start on a course in Numerical methods and programming we should look at some of the basic aspects of programming. We will learn here, how to convert some of our ideas into a working