C Programming Concepts and Algorithms

Algorithms to Programs

• Algorithms are sets of instructions to accomplish a task.
• C Programs are formal expressions of algorithms compiled by computers (compilers).
• Algorithms are expressed in plain English, pseudocode, and flowcharts.
• Programs are "compiled" into machine language.

Writing, Editing, Compiling, and Linking Programs in C

• Writing and editing is done using text editors and source files.
• The compiler converts source code into machine language.
• The compiler has two parts: the preprocessor and the translator.
• The preprocessor processes preprocessor directives.
• The translator reads translation units and writes resulting objects.
• The linker combines all functions to create an executable file.

Key Parts of a C Program

• Preprocessor directives include standard input/output functions using #include.
• The int main() function is the entry point for all C programs.
• Statements contain instructions inside the function.
• The return 0; statement ends the program.

Values and Variables

• There are four basic types:
  • Integers (int): Whole numbers (e.g., 0, 1, -1).
  • Floating-point numbers (float): Numbers with fractions (e.g., 1.0, 0.5).
  • Characters (char): Single characters (e.g., 'A', 'z').
  • Character strings (char-s): Sequences of characters (e.g., "Hello World")

Expressions

• Expressions combine values, variables, and operators to produce a result.
• Arithmetic operators include:
  • + (addition), - (subtraction)
  • * (multiplication), / (division)
  • % (modulus - remainder of division)
• Operator precedence is defined by PEMDAS:
  • Parentheses → Order of exponents → Division/Multiplication → Addition/Subtraction.

Function Calls

• A function call invokes a set of instructions by name.

Comments

• Comments document code for clarity.
• Comments are ignored during execution.
• Single-line comments are indicated by //.
• Multi-line comments are enclosed within /* */.

Types and Variables

• Types define the kind of data a value holds.
• Built-in types include: char, int, and float.
• Type modifiers include long, short, and const.
• User-defined types include arrays and structures.
• Strings are arrays of char.

Character Representation

• ASCII (American Standard Code for Information Interchange) stores characters as integers.
• ASCII values range from 0 (NUL) to 127 (DEL).
• 'A' has an ASCII value of 65.
• Values from 128 to 255 are considered "extended" ASCII sets.

Floating Point

• Floating-point numbers represent fractional values, such as 789.34.
• C supports three sizes of floating-point data:
  • float: 4 bytes
  • double: 8 bytes
  • long double: 10 bytes
• Floating-point size is machine-dependent.
• sizeof provides the exact size in bytes.
• Floating-point values are always signed.

Variables

• Variables are logical names for containers that hold data.
• Variables have an associated type.
• Variables must be declared before use:
  • [modifiers] [type] [name]; (without assignment)
  • [modifiers] [type] [name] = [value]; (with assignment)

Keywords and Identifiers

• Keywords are reserved words in C with special meanings (e.g., int, float, if, else).
• Keywords cannot be used as variable names.
• Identifiers are names for variables, functions, etc.
• Identifiers must begin with a letter or underscore and are case-sensitive.

Assignments

• The assignment operator = assigns a value to a variable.

Constant Variables

• Constant variables, also known as global variables, cannot change their value after assignment.
• Constants are declared using the const keyword.

Booleans

• There is no built-in Boolean type in C; integers are used instead.
• 0 represents false, and any non-zero value represents true.
• Booleans are used for conditions (selection and looping).

Boolean Expressions and Operators

• Boolean operators include:
  • && (AND): True if both conditions are true.
  • || (OR): True if at least one condition is true.
  • ! (NOT): True if the condition is false.
  • == (Equality): Checks for equality.
  • != (Inequality): Checks for inequality.
  • <, >, <=, >= (Comparison operators)

Formatted Input/Output

• Formatted input/output (I/O) refers to how data is read from and written to input/output streams using specific formats.
• scanf() and printf() functions control the input and output formats.

Streams

• Streams are sequences of characters organized into lines, serving as channels for data transfer between programs and I/O.
• They consist of zero or more characters, ending with a newline character \n.
• Text input/output is handled as a sequence of characters.

Standard Streams

• stdin: Standard input, typically from the keyboard.
• stdout: Standard output, typically to the screen.
• stderr: Standard error, typically to the screen.
• #include <stdio.h> is required for I/O operations.
• Streams can be redirected.

Formatted Input: scanf()

• Reads data from the standard input stream.
• Syntax: scanf(format-control-string, &variable1, &variable2, …);
• Use & for non-string variables (e.g., integers, floats).
• Do not use & for strings.

Formatted Output: printf()

• Writes formatted data to the standard output stream.
• Syntax: printf(format-control-string, variable1, variable2, …);

Conversion Specifiers

• Used in printf() and scanf().
• Common conversion specifiers include:
  • %d: Decimal integer
  • %f: Float
  • %c: Character
  • %s: String

Precision Modifiers

• Used with floating-point numbers to limit the number of decimal places (e.g., %.2f).

Width Modifiers

• Control the minimum number of positions for output.

Common Conversion Specifiers

• Numeric:
  • %d: Decimal integer
  • %f: Floating-point number
• Alphanumeric:
  • %c: Character
  • %s: String

Data File I/O

• File I/O allows programs to interact with data files for reading and writing data.

Types of Files in C

• Text files:

  • Store data in ASCII character format.
  • Each line ends with a newline character \n.
  • Can be read or edited using a text editor.
  • Typically use the .txt file extension.

• Binary files:

  • Store data in binary form (0s and 1s).
  • Created and read only through programs.
  • Not human-readable.
  • Typically use the .bin file extension.

Three Steps for Accessing Data Files

1. Opening the file: Using the fopen() function.
2. Reading/writing data: Using fscanf() for reading or fprintf() for writing.
3. Closing the file: Using the fclose() function.

Opening a Data File: fopen()

• Declare a file stream pointer: FILE *fptr;
• Use fopen() to open the file: fptr = fopen("data.txt", "wt");
  • The first argument is the filename.
  • The second argument is the mode:
    • "w" or "wt": Open an ASCII file for writing.
    • "r" or "rt": Open an ASCII file for reading.
    • "a" or "at": Open an ASCII file for appending.
    • "wb": Open a binary file for writing.
    • "rb": Open a binary file for reading.
    • "ab": Open a binary file for appending.

Closing a Data File: fclose()

• Close the file using fclose() after finishing file operations: fclose(fptr);

Writing to an ASCII Data File: fprintf()

• Syntax: fprintf(file_pointer, format_specifiers, data);
• Example: fprintf(fptr, "%d\n", x);
  • fptr: The file stream pointer.
  • format_specifiers: Same as printf(), including format specifiers (e.g., %d for an integer).

Reading from an ASCII Data File: fscanf()

• Syntax: fscanf(file_pointer, format_specifiers, &variable);
• Example: fscanf(fptr, "%d", &x);

This quiz covers key concepts in C programming, focusing on algorithms, writing and editing code, compiling, and linking. Explore how algorithms translate into C programs and the essential components that make up a typical C program.