Lab Sheet 1

Lab Sheet 1

Review of Important Concepts in C

1. Loops in C

Loops execute a block of code repeatedly until a condition becomes false.

Types of Loops

In C, there are three types of loops: for loop, while loop, and do-while loop.

A. for Loop

Used when the number of iterations is known. It contains initialization, loop condition, and increment/decrement parts within the loop construct itself. In this loop, the loop condition is checked at the beginning.

Syntax:

for(initialization; condition; increment)
{
    statements;
}

Example:

for(int i=1; i<=5; i++)
{
printf("%d\n", i);
}

B. while Loop

Checks the condition before execution. It checks the condition during the loop entry. The increment or decrement logic has to be placed inside the loop explicitly.

Example:

int i=1;
while(i<=5)
{
printf("%d\n", i);
i++;
}

C. do-while Loop

It is an exit-controlled loop. The loop condition is checked at the last part of the loop. So that the loop executes at least once.

Example:

int i=1;
do
{
printf("%d\n", i);
i++;
}
while(i<=5);

Applications

• Menu-driven programs

• Searching

• Sorting

• Repeated calculations

2. Nested Loops

A loop inside another loop is called a nested loop. Nested loops are required if a repetition is to be repeated itself.

Structure

for(...)
{
for(...)
{
    statements;
}
}

Example

for(int i=1;i<=3;i++)
{
for(int j=1;j<=3;j++)
{
    printf("* ");
}
printf("\n");
}

Output:

* * *
* * *
* * *

Applications

• Pattern printing

• Matrix operations

• Multiplication tables

Example: Multiplication Table

for(int i=1;i<=5;i++)
{
for(int j=1;j<=10;j++)
{
        printf("%4d", i*j);
}
printf("\n");
}

3. Functions in C

A function is a self-contained block of code that performs a specific task. Functions improve program organization, code reusability, readability, and maintainability.

Functions allow programmers to divide a large program into smaller modules. Each function can be developed and tested independently.

Advantages of Functions

• Code reusability

• Reduced program complexity

• Easier debugging

• Better maintainability

• Supports modular programming

Syntax

return_type function_name(parameters)
{
// Function body
}

Types of Functions

Functions are categorized into Library Functions and User-Defined Functions based on the source of their definition and implementation.

1. Library Functions

   • printf()

   • scanf()

   • strlen()

2. User-defined Functions

Example

#include <stdio.h>
int add(int a, int b)
{
return a + b;
}

int main()
{
int result = add(5, 10);
printf("Sum = %d", result);
return 0;
}

Function Categories

The following are the function categories according to return values and arguments.

1. No arguments, no return value

2. Arguments, no return value

3. No arguments, return value

4. Arguments and return value

4. Recursion

Recursion is a process in which a function calls itself directly or indirectly.

Every recursive function must contain:

1. Recursive logic

2. Terminating condition

Not every problem can be solved recursively.

Advantages

• Simplifies complex problems

• Useful for tree and graph algorithms

Example: Factorial

Mathematical Formula:

n! = n × (n−1)! 

Program:

#include <stdio.h>
int factorial(int n)
{
if(n==0)
    return 1;

return n * factorial(n-1);
}

int main()
{
printf("%d", factorial(5));
return 0;
}

Recursion Process

factorial(5)
= 5 × factorial(4)
= 5 × 4 × factorial(3)
= 5 × 4 × 3 × factorial(2)
= 5 × 4 × 3 × 2 × factorial(1)
= 120

5. Arrays in C

An array is a collection of elements of the same data type stored in contiguous memory locations.

Advantages

• Efficient storage of multiple values

• Easy traversal

• Supports sorting and searching

Syntax

data_type array_name[size];

Example:

int marks[5];

Initialization

int marks[5] = {10,20,30,40,50};

Accessing Elements

printf("%d", marks[2]);

Array Traversal

for(int i=0;i<5;i++)
{
printf("%d ", marks[i]);
}

Memory Representation

Index: 0  1  2  3  4
Value:10 20 30 40 50

6. Strings in C

A string is an array of characters terminated by a null character (\0).

Declaration

char name[20];

Initialization

char name[] = "Hello";

Memory:

H e l l o \0

Input and Output

scanf("%s", name);
printf("%s", name);

String Functions

The following are some of the string library functions.

strlen(): Length of string

strcpy(): Copy one string to another

strcat(): Concatenate two strings

strcmp(): Compare strings lexicographically

Example

#include <stdio.h>
#include <string.h>
int main()
{
char str[]="Programming";
printf("Length=%d", strlen(str));
return 0;
}

Output:

Length=11

7. Pointers

A pointer is a variable that stores the memory address of another variable.

Declaration

int *ptr;

Pointer Operators

The following are the operators related to pointers.

&: Address of

*: Value at address

Example

int x = 10;
int *ptr = &x;

printf("%d", *ptr);

Output:

10

Advantages

• Dynamic memory allocation

• Efficient array handling

• Function parameter passing

• Data structure implementation

8. Structures

A structure is a user-defined data type that groups different data types under one name.

Syntax

struct Student
{
int roll;
char name[20];
float marks;
};

Example

#include <stdio.h>
struct Student
{
int roll;
char name[20];
float marks;
};

int main()
{
struct Student s1;

s1.roll = 101;
s1.marks = 89.5;
printf("%d %.2f", s1.roll, s1.marks);

return 0;
}

Advantages

• Organizes related data

• Represents real-world entities

• Foundation for advanced data structures

Array of Structures

struct Student s[3];

Useful for storing multiple structure-type records; students in the above.

9. File Handling in C

File handling enables permanent storage of data on secondary storage devices.

File Operations

1. Create

2. Open

3. Read

4. Write

5. Append

6. Close

File Pointer

FILE *fp;

Opening a File

fp = fopen("data.txt","w");

File Modes

The following are different file modes.

r: Read

w: Write

a: Append

r+: Read and Write

w+: Read and Write

a+: Read and Append

Writing to a File

Example

#include <stdio.h>
int main()
{
FILE *fp;
fp = fopen("data.txt","w");
fprintf(fp,"Hello File");
fclose(fp);
return 0;
}

Reading from a File

char text[100];
fp = fopen("data.txt","r");
fgets(text,100,fp);
printf("%s", text);
fclose(fp);

Functions for File I/O

The following are some of the functions useful in reading from a file and writing into it.

fgetc(): Reads the next character from the specified file stream and advances the file pointer. 

fputc(): Writes a single character to the specified file stream and advances the position indicator.

fgets(): Reads a line of string from the stream.

fputs(): Writes a null-terminated string to the specified file stream. 

fscanf(): Reads formatted data from the file stream into specified variable addresses, similar to scanf().

fprintf(): Writes formatted text and data to the file stream, similar to printf().

fread(): Reads a specified number of elements, each of a specific byte size, from the file stream.

fwrite(): Writes a specified number of elements of a given byte size directly into the file stream.

Applications

• Student management systems

• Banking systems

• Inventory systems

• Database storage

Exercises  

1. Write a program to calculate the sum of the following series, correct up to four decimal places. Make a user-defined function that calculates the sum of the following series and returns the value. Read the value of x in degrees, and pass it to your function that returns the sum.

sin(x) = x - x^3/3! + x^5/5! - x^7/7! + ...

2. Write a program to find the golden ratio correct up to four decimal places using the Fibonacci series. Create your own recursive function to return the next Fibonacci number.

3. Write a program to read the monthly expenditure of a company for a range of years specified by the user. Use an array to construct a table of expenditures and display it in that form. Calculate and display the following:

   • The total expenditure for each year.

   • The average monthly expenditure for each year.

   • The total expenditure for the entire range of years.

   • The average yearly expenditure in that range of years.

   • The average monthly expenditure over the entire range of years.

4. Write a program to find all positions of a character specified by the user in a sentence of text entered by the user using pointers and strings (character array).

5. Write a program to read and display the names of students and their obtained marks in programming using an array of structures. Display the list of students and marks obtained according to marks in descending order.

6. Write a program to read the name, roll number, address, and phone number of each student in your class using structures. Store the information in a file so that you can recover it later. Read the records back from the file, sort the records alphabetically by name, and display the sorted list.