Introduction to C Language

1. Contains comments that describe the program.

2. Useful for providing details like program purpose, author name, and creation date.

3. Example

/* Program to demonstrate the structure of a C program

   Author: John Doe

   Date: 2023-12-11

*/

1. Main Function: Every program must have a main() function as the entry point.

2. Case Sensitivity: C is case-sensitive (e.g., Var and var are different).

3. Semicolons: End each statement with a semicolon (;).

4. Preprocessor Directives: Use #include for header files and #define for constants.

5. Variable Rules: Declare variables before use, with valid names and correct data types.

6. Functions: Define reusable functions with proper prototypes and return types.

7. Input/Output: Use printf for output and scanf for input, matching format specifiers.

8. Comments: Add comments for clarity using // or /* */.

9. Indentation: Write neatly formatted and indented code for readability.

10. Return Statement: Use return 0; in main() to indicate successful execution.

The character set of C includes all the valid characters used in writing C programs:

1. Letters: Uppercase (A-Z) and lowercase (a-z).

2. Digits: Numbers from 0-9.

3. Special Characters: Symbols like ~ ! @ # % ^ & * ( ) - + = { } [ ] ; : ' " < > , . ? / \ |.

4. White Spaces: Space, tab (\t), newline (\n), etc.

5. Escape Sequences: Special character representations like \n (newline), \t (tab), \\ (backslash), etc.

6. Underscore (_): Used in identifiers like variable names.

Keywords in C

Keywords are reserved words in C that have predefined meanings and cannot be used as identifiers (variable, function, or constant names). They are essential for writing C programs.

• Examples:
  int, float, char, if, else, for, while, return, switch, break, continue, void, struct, etc.

• Rules:

  • Keywords are case-sensitive.

  • Cannot be redefined or used for other purposes.

Format Specifiers in C

Format specifiers are placeholders used in input/output functions (printf and scanf) to represent the type of data being processed.

• Common Specifiers:

  • %d : Integer

  • %f : Float

  • %c : Character

  • %s : String

  • %lf : Double

  • %u : Unsigned integer

  • %x : Hexadecimal

  • %o : Octal

• Example:

  c

  Copy codeint num = 10;

  printf("Number: %d", num); // Output: Number: 10

  
  

Constants in C

Constants are fixed values that do not change during program execution.

1. Types of Constants:

   • Integer constants: Whole numbers (e.g., 10, -20).

   • Floating-point constants: Decimal numbers (e.g., 3.14, -0.5).

   • Character constants: Single characters enclosed in single quotes (e.g., 'A').

   • String constants: Sequence of characters enclosed in double quotes (e.g., "Hello").

2. Defining Constants:

   • Using #define:

     c

     Copy code#define PI 3.14

     
     

   • Using const keyword:

     c

     Copy codeconst int age = 25;

     
     

Example Program

c

Copy code#include <stdio.h>

#define PI 3.14  // Constant definition

int main() {

    const int year = 2023; // Constant

    int radius = 5;

    printf("Radius: %d\n", radius);      // Format specifier: %d

    printf("PI: %.2f\n", PI);            // Format specifier: %.2f

    printf("Year: %d\n", year);          // Format specifier: %d

    return 0;

}

The if statement in C is used to execute a block of code only when a specified condition evaluates to true (non-zero).

Syntax:

c

Copy codeif (condition) {

    // Code to execute if the condition is true

}

Key Points:

1. Evaluates a logical or relational condition.

2. If the condition is true, the code inside the if block runs; otherwise, it is skipped.

3. Braces {} are optional for single statements but recommended.

Example:

c

Copy codeint num = 10;

if (num > 5) {

    printf("The number is greater than 5.\n");

}

Output: The number is greater than 5.

The if-else statement in C is used to execute one block of code if a condition is true and another block if the condition is false.

Syntax:

c

Copy codeif (condition) {

    // Code to execute if the condition is true

} else {

    // Code to execute if the condition is false

}

Example:

c

Copy codeint num = 10;

if (num % 2 == 0) {

    printf("Even number\n");

} else {

    printf("Odd number\n");

}

Output: Even number

The if-else statement ensures decision-making between two mutually exclusive outcomes.

A nested if-else statement in C is an if-else statement placed inside another if or else block, allowing for multiple conditions to be checked in sequence.

Syntax:

c

Copy codeif (condition1) {

    if (condition2) {

        // Code to execute if both condition1 and condition2 are true

    } else {

        // Code to execute if condition1 is true and condition2 is false

    }

} else {

    // Code to execute if condition1 is false

}

Example:

c

Copy codeint num = 10;

if (num > 0) {

    if (num % 2 == 0) {

        printf("Positive even number\n");

    } else {

        printf("Positive odd number\n");

    }

} else {

    printf("Non-positive number\n");

}

Output: Positive even number

A nested if-else statement allows for more complex decision-making with multiple conditions.

lse-If Ladder in C

An else-if ladder is a chain of multiple if-else conditions used when there are more than two possible conditions to check. It allows the program to test multiple conditions sequentially.

Syntax:

c

Copy codeif (condition1) {

    // Code if condition1 is true

} else if (condition2) {

    // Code if condition2 is true

} else if (condition3) {

    // Code if condition3 is true

} else {

    // Code if none of the above conditions are true

}

Example:

c

Copy codeint num = 10;

if (num > 0) {

    printf("Positive\n");

} else if (num < 0) {

    printf("Negative\n");

} else {

    printf("Zero\n");

}

Output: Positive

Switch-Case in C

The switch-case statement is used to handle multiple possible values of a variable, making the code more readable when there are many conditions based on the same variable.

Syntax:

c

Copy codeswitch (expression) {

    case value1:

        // Code to execute if expression == value1

        break;

    case value2:

        // Code to execute if expression == value2

        break;

    default:

        // Code to execute if no case matches

}

Example:

c

Copy codeint day = 3;

switch (day) {

    case 1:

        printf("Monday\n");

        break;

    case 2:

        printf("Tuesday\n");

        break;

    case 3:

        printf("Wednesday\n");

        break;

    default:

        printf("Invalid day\n");

}

Output: Wednesday

Key Differences:

• Else-if Ladder: Best for evaluating complex or varied conditions.

• Switch-case: Ideal for checking multiple potential values of a single variable.

Unconditional statements in C are commands that are always executed, regardless of any conditions. These statements control the flow of execution without any condition or decision-making.

Types of Unconditional Statements:

1. break:

   • Exits from a loop (for, while, do-while) or a switch statement, terminating the current block of execution.

   c

   Copy codewhile (1) {

       break;  // Exits the loop

   }

   
   

2. continue:

   • Skips the current iteration of a loop and proceeds with the next iteration.

   c

   Copy codefor (int i = 0; i < 5; i++) {

       if (i == 2) {

           continue;  // Skips iteration when i is 2

       }

       printf("%d ", i);

   }

   
   

3. return:

   • Exits from a function and optionally returns a value to the caller. In main(), it typically returns an integer indicating the program's status.

   c

   Copy codereturn 0;  // Exits the function and returns 0

   
   

These statements control the flow of execution directly, without any conditional checks.