What is a Programming Language?

A programming language is a formal set of rules and instructions used by programmers to write computer programs.

Computers ultimately work using binary values 0 and 1. Programming languages allow humans to write instructions in a more understandable form before those instructions are translated into machine code.

Basic Program Development Process

1. Understand the problem.
2. Design the solution.
3. Prepare an algorithm, flowchart or pseudocode.
4. Write the source code.
5. Translate or compile the program.
6. Run and test the program.
7. Find and correct errors.

Low Level Language

A low-level language works close to computer hardware.

It includes machine language and assembly language.

• Very fast execution.
• Harder for humans to understand.
• Machine dependent.

High Level Language

A high-level language uses English-like words and readable syntax.

Examples include C, C++, Java and Python.

• Easier to write.
• Easier to understand and debug.
• Must be translated into machine language.

Fourth Generation Language – 4GL

A fourth-generation language is designed to solve specific problems using fewer instructions than traditional programming languages.

A control structure determines the order in which program statements are executed.

Algorithm

An algorithm is a step-by-step procedure for solving a problem.

A good algorithm should be:

• Finite
• Definite
• Effective

Flowchart

A flowchart is a graphical representation of an algorithm using standard symbols.

Pseudocode

Pseudocode is a code-like description of program logic written using simple English rather than strict programming syntax.

Example: Find Largest of Two Numbers

BEGIN

READ A, B

IF A > B THEN
    PRINT "A is largest"
ELSE
    PRINT "B is largest"
END IF

END

Absolute Binary

Absolute binary represents information directly using 0s and 1s.

BCD – Binary Coded Decimal

BCD represents each decimal digit separately using a 4-bit binary code.

ASCII

ASCII stands for American Standard Code for Information Interchange.

It assigns numeric values to English letters, numbers, symbols and control characters.

Unicode

Unicode is a character encoding system designed to represent text from many writing systems around the world.

It allows computers to display languages such as English and Devanagari together.

C is a general-purpose, procedural programming language developed by Dennis Ritchie at Bell Laboratories in the early 1970s.

Features of C

#include <stdio.h>

int globalVar = 10;

void myFunction();

int main()
{
    int localVar = 20;

    printf("Hello, World!\n");
    printf("Global variable: %d\n", globalVar);
    printf("Local variable: %d\n", localVar);

    myFunction();

    return 0;
}

void myFunction()
{
    printf("This is a user-defined function.\n");
}

Main Parts

• Preprocessor Directive: Instructions beginning with #, such as #include.
• Global Variable: Declared outside all functions.
• main(): The main function where program execution begins.
• Local Variable: Declared inside a function.
• return 0: Indicates successful program termination.

C Preprocessor and Header Files

Preprocessor directives are processed before compilation.

• #include – includes a header file.
• #define – defines a macro or symbolic constant.

Character Set in C

• Uppercase alphabets A–Z
• Lowercase alphabets a–z
• Digits 0–9
• Special symbols
• Spaces, tabs and newline characters

Comments in C

// Single-line comment

/*
   Multi-line
   comment
*/

Identifier

An identifier is a name given to program elements such as variables and functions.

Examples: total, studentAge, calculateArea

Keyword

Keywords are reserved words with predefined meanings in C.

Examples: int, float, if, else, while, return

Token

Tokens are the smallest individual units recognized by the C compiler.

They include:

• Keywords
• Identifiers
• Constants
• Operators
• Punctuation

Rules for Identifiers

• Must begin with a letter or underscore.
• Can contain letters, digits and underscores.
• Cannot contain spaces.
• Cannot use reserved keywords.
• C identifiers are case-sensitive.

Variable

A variable is a named memory location whose value can change while the program executes.

int score = 0;

Constant

A constant is a value that does not change during program execution.

Types include:

• Integer constant – 10
• Floating constant – 3.14
• Character constant – ‘A’
• String constant – “Nepal”

const float PI = 3.14159;

#define PI 3.14159

Type Specifiers

C provides type specifiers such as:

• short
• long
• signed
• unsigned

Simple and Compound Statements

A simple statement is a single instruction ending with a semicolon.

a = a + 1;

A compound statement contains several statements inside curly braces.

An operator is a symbol that performs an operation. An expression combines operators and operands to produce a value.

C commonly uses printf() for output and scanf() for input.

#include <stdio.h>

int main()
{
    int rollNo;
    char grade;
    float percentage;

    printf("Enter your Roll Number: ");
    scanf("%d", &rollNo);

    printf("Enter your Grade: ");
    scanf(" %c", &grade);

    printf("Enter your Percentage: ");
    scanf("%f", &percentage);

    printf("\nRoll Number: %d\n", rollNo);
    printf("Grade: %c\n", grade);
    printf("Percentage: %.2f%%\n", percentage);

    return 0;
}

Common Format Specifiers

• %d – integer
• %f – float
• %c – character
• %s – string
• \n – new line
• \t – tab space

if Statement

int age = 19;

if(age >= 18)
{
    printf("You are eligible to vote.");
}

if-else Statement

int marks = 65;

if(marks >= 40)
{
    printf("You have passed.");
}
else
{
    printf("You have failed.");
}

Nested if / if-else-if

int num = 10;

if(num > 0)
{
    printf("Positive\n");

    if(num % 2 == 0)
        printf("Even");
    else
        printf("Odd");
}
else if(num < 0)
{
    printf("Negative");
}
else
{
    printf("Zero");
}

switch Statement

char grade = 'B';

switch(grade)
{
    case 'A':
        printf("Excellent!");
        break;

    case 'B':
        printf("Good job!");
        break;

    case 'C':
        printf("Satisfactory.");
        break;

    default:
        printf("Invalid grade.");
}

for Loop

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

while Loop

int i = 1;

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

do-while Loop

int i = 1;

do
{
    printf("%d\n", i);
    i++;

} while(i <= 5);

An array is a collection of elements of the same data type stored under one variable name.

One-Dimensional Array

int studentMarks[5] = {75, 80, 65, 90, 88};

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

Two-Dimensional Array

A two-dimensional array stores elements in rows and columns.

int matrix[2][3];

Matrix Addition Logic

for(i = 0; i < 3; i++)
{
    for(j = 0; j < 3; j++)
    {
        c[i][j] = a[i][j] + b[i][j];
    }
}

A string in C is an array of characters ending with the null character \0.

#include <stdio.h>
#include <string.h>

int main()
{
    char name[20] = "Kathmandu";
    char city[20];
    char greeting[30] = "Namaste";

    printf("Length: %d\n", strlen(name));

    strcpy(city, name);
    printf("Copied: %s\n", city);

    strcat(greeting, " Nepal!");
    printf("Combined: %s\n", greeting);

    return 0;
}

1. Sum of Two Numbers

#include <stdio.h>

int main()
{
    int a, b, sum;

    printf("Enter two numbers: ");
    scanf("%d %d", &a, &b);

    sum = a + b;

    printf("Sum = %d", sum);

    return 0;
}

2. Check Even or Odd

#include <stdio.h>

int main()
{
    int n;

    printf("Enter a number: ");
    scanf("%d", &n);

    if(n % 2 == 0)
        printf("%d is Even", n);
    else
        printf("%d is Odd", n);

    return 0;
}

3. Factorial Using Loop

#include <stdio.h>

int main()
{
    int i, n, fact = 1;

    printf("Enter a number: ");
    scanf("%d", &n);

    for(i = 1; i <= n; i++)
    {
        fact = fact * i;
    }

    printf("Factorial = %d", fact);

    return 0;
}

4. Sum and Average Using Array

#include <stdio.h>

int main()
{
    int numbers[5], sum = 0, i;
    float average;

    printf("Enter 5 numbers:\n");

    for(i = 0; i < 5; i++)
    {
        scanf("%d", &numbers[i]);
        sum += numbers[i];
    }

    average = (float)sum / 5;

    printf("Sum = %d\n", sum);
    printf("Average = %.2f\n", average);

    return 0;
}

5. Input and Display 2 × 3 Matrix

#include <stdio.h>

int main()
{
    int matrix[2][3], i, j;

    printf("Enter matrix elements:\n");

    for(i = 0; i < 2; i++)
    {
        for(j = 0; j < 3; j++)
        {
            scanf("%d", &matrix[i][j]);
        }
    }

    printf("\nMatrix:\n");

    for(i = 0; i < 2; i++)
    {
        for(j = 0; j < 3; j++)
        {
            printf("%d\t", matrix[i][j]);
        }

        printf("\n");
    }

    return 0;
}

6. Reverse a String

#include <stdio.h>
#include <string.h>

int main()
{
    char name[50];

    printf("Enter a string: ");
    scanf("%s", name);

    strrev(name);

    printf("Reversed = %s", name);

    return 0;
}