Chapter 5

 

Selection sort

for(i=0; i< n-1; i++)

         for(k=i+1; k<n; k++)

                 if(x[i] > x[k])

                          swap( );

Bubble sort

for(i=0; i< n; i++)

         for(k=0; k<n-1; k++)

                 if(x[k] > x[k+1])

                          swap( );

 

Insertion sort

for(i=1; i< n; i++)

         for(k=0; k<i; k++)

                 if(x[i] < x[k])

                          swap( );

 

·      Write a program to find factorial of an input number using iterative method

·      Write a program to find factorial of an input number using recursive method

 

 

 

Steps of Programming

 

1.      Planning a C program

Before beginning actual program, it is necessary to analyze detail of the problem to be solved. A programmer should concentrate on general program logic without focusing on syntactic details. This process may repeat many times with more programming details. So initially, only module names are used to solve but then after such modules are written in detail. Such method of solving problem is known as top-down programming.

 

There is another method of programming, in which useful self-contained modules (user defined functions) are written first. After detail development of such modules, they are combined together to form a program. This method of programming is known as bottom-top programming approach.

 

 

2.      Writing outline of program

In order to solve a problem using a computer, it must be expressed the solution to the problem in terms of the instructions of the particular computer. A computer program is actually just a collection of the instructions necessary to solve a specific problem. The approach or method that is used to solve the problem is known as algorithm.

 

         Such an algorithm, is written with informal outline which consist of phrases or sentences that are part in English and part in C language. In this stage of development of program, amount of C codes are minimum used, only used for major components such as function headings, function references, control statements describing major program components. Additional details are described in English. So the resulting outline of details of program is known as pseudocode.

 

Here is an example of pseudocode to find the square root of an input number.

Step 1:      Start the program.

Step 2:      Declare x, sqrt and n as floating point variable, initializing the value of n as 0.5.

Step 3:      find the antilog for product of n and log of x, then store it to sqrt variable.

Step 4:      print the value of sqrt variable

Step 5:      end of program.

 

Here is a pseudocode to print prime numbers from 1to 100.

 

Step 1:      fill an array num[100] with numbers 1 to 100

Step 2:      starting with the second entry in the array, set all it multiple to zero.

Step 3:      proceed to next non-zero element and set all it’s multiple to zero.

Step 4:      repeat step 3 till you have setup the multiples of all the non zero elements to zero.

Step 5:      at the conclusion of step 4, all the non-zero entries left in the array would be prime numbers, so print out these numbers.

 

Here is a pseudocode to print integer numbers from 1 to 10.

Step 1:      start the program

Step 2:      initialize the value of i to 1

Step 3:      print value of i and increase it by 1

Step 4:      repeat step 3 till value of i is less than 11

Step 5:      end of program

 

 

3.      Flow chart

After the development of algorithm, the flow of control of instruction can be shown in pictorial form. Such pictorial form of execution of instructions is known as flow chart. It makes programmer and any other user can easily understand the algorithm of program if the program is to be debugged or to be modified in future.

Writing a C program (Coding)

Once an overall program strategy has been formulated and program outline has been developed, it is to be coded in programming language like C. At this stage, each component of program is carefully to be translated into equivalent C instructions in details. Each instruction should be written in right ordered (sequence), correct and readable (use of indentation, comments and clearly labeled) with proper declarations.

 

Compiling & Executing program

         Once a complete program has been correctly entered into the computer, it can be compiled and executed. The program can either be compiled & run using compile & run option in menu or using command prompt.

e.g   

         tcc name

 

tcc test.cpp                 for both compile and run

         tcc –c test.cpp    for only to compile

 

Error Diagnostics

While attempting to compile and run the program, it may list some errors because of improperly declared variables, reference to undeclared variables or improper use of punctuation. Such type of error is known as syntax (grammatical) error or Compile time error. The compiler will automatically generate diagnostic messages for such errors.

 

         It may display error after successfully compilation of program. Such type of error occured during execution of program, because of boundary limit of type of variable, division by zero, square roof of negative no. etc.  Such error is known as execution error or Run time error.

 

         After successfully, compilation and execution of program, it may still display incorrect result after determining the expression because of improper use of logic during problem analysis, and such type of error is known as logical error.

 

Overflow and underflow errors

Sometime working in a data item in C, it may exceed beyond the capacity of the data item which is known as overflow error. And similarly, it may goes down to its lower limit then it is known as underflow error.

e.g. int x=32767;

 if the value of x is increased beyond it’s limit, then it again starts from -32768. This type of error is known as overflow error.

 

Detecting error (Debugging)

         It is easy to find out syntax error in the program, since it is automatically detected and listed while compiling the program. It displays error with instruction line number.

 

         Execution and logical errors may occur at some circumstances only, so for detecting such errors, the program must be thoroughly checked by supplying various data. Each calculation is to be carried out for known answer or by calculating using calculator.

 

         If the error cannot be located simply by inspection, the program should be modified to print out certain intermediate results and then be re-run. This technique is referred to as tracing.

 

Documentation

         Once a system is implemented and in full operation, it is to be examined to see if it has met the objectives set out in original specification. Unforeseen problems may overcome in future or the program is to be modified to fulfill future requirement. So, it will be easier for such amendments in the program by any programmer, if properly documented the program with necessary diagrams, algorithm, flowcharts, coding, user guide and limitations are included.

 

 

 

 

 

Structured programming

In properly structured program, sets of actions are grouped together in units that are, self contained syntactically for the compiler and visually for human reader.

 

C encourages the division of a program into many small routines, called function, with self defined, interfaces and an efficient calling mechanism. Function can call other functions including themselves. Such a method of programming that breaks a program into many modules with clarity is known as structure programming.

 

Within each function, the code is structured into blocks using { and }
 as block markers. Blocks can be nested to any level however large or small. The control enters only at the start of block and emerges eventually only at the bottom.

 

Advantages of structure programming

Accuracy, readability and maintainability

 

Maintainability:

Most programs eventually require maintenance whether or not they are maintainable. Programs that are different to understand are hard to update without causing damage with the change. If unstructured, the cost of maintenance of program becomes high. So it may require to discard such program. If structured, the life of program prolong by maintaining it.

 

Clarity:

Structured program are more readable with compare the unstructured. Any logical error can be easily debugged & solved. Since, it is easy to check only with the module having error.

 

Accuracy:

Since the program can easily be debugged & is free of any logical error, any one gets desired result with accuracy.

 

2. What are the components of a program? What is the one component that must be present in every C program? (2055 -10)

A program written in C, consist of many components. The major components of the program are:

1)              Comments :

Any text entered between /* and */ or after // is ignored by the compiler. Comments are used to remark certain programmer reference text such as version number, authorship, dates, copyright as well as various explanations of different modules & instructions.

2)              Include directive :

Generally it consists of header file & library file such as stdio.h. It includes necessary codes of any library functions used in the program from respective header/ library file.

3)              Defining symbolic constant & macros :

In this section, constant is defined as macros, which during preprocessing the preprocessor replaces every occurrence with respective constants in the program.

e.g. # define      PI       3.1415

 

printf(“ The Yankee virus”);

 

4)              Main function:

It is the most important component of a program which must be present in every program. There may be other self contained functions in a program. Such function may be defined either before or after main function but the program execution always begins from main function wherever it is positioned.

5)              Block markers (compound statement) :

{ } curly braces are used to signal the start and end of a block of codes. They play the same rose as BEGIN and END in other structure language. There may be a number of block markers to represent each block of statements. It is also known as compound statement. But there must be equal number of opening & closing of block markers.

6)              Declarations :

At      the beginning of main function, all variables should be defined with the data type that may be stored during the execution of program. Such declaration of variables, actually reserve space into memory. The declaration of variable allocates number of bytes into memory such as 2, 4, 8, 1 byte for int, float, double, & char respectively.

It also must be declared a function if the function is defined after the main function which is known as function prototype of the function. It contains type of function it returns value and function name followed with number of arguments as it is defined in function definition.

7)              Statements :

One or more statements can be enclosed within main function. It may be used number of library functions, user defined functions, expression statements etc. such statements will be executed one after another. But such execution can be controlled by control statements like if…else, for, while, do… while, switch etc.

 

Let’s see an example of program to find area of a circle for an input radius using function.

 

#include<stdio.h>

#include<math.h>

 

#define PI 3.1415

 

void main()

{

          int rad;

          float a;

          float area (float r);

          printf(“\n Enter radius of circle”);

          scanf(“%d”,&rad);

          a=area(rad);

          printf(“\n Area of circle is : %f”,a);

}

 

float area(float r)

{

          return(PI*pow(r,2));

}

 Full Width