C Programming: Stages, Errors

C Programming Basics

• Computer programming involves creating a sequence of instructions for a computer
• A programming language is an artificial language to control a machine's behavior, especially a computer.

Stages of Computer Programming

• Problem statement: Start with a clear written definition of the problem
• Algorithm development: Create a program logic to accomplish the task, visualized with tools like flowcharts.
  • Algorithm is a set of steps to accomplish a task
• Program coding: Convert the logic into a programming language's specific syntax
• Program testing: Check the coded program for errors
• Program documentation: fully document complete programming process

Common Programming Errors

• Syntax error: Violates grammar rules, detected by the compiler, preventing translation and execution
• Run-time error: Detected during program execution, usually due to illegal operations, halting the program
• Logic error: Program follows a faulty algorithm, difficult to detect, resulting in incorrect output

Turbo C History and Definition

• Turbo C was created by Dennis MacAlistair Ritchie at AT&T Bell Laboratories
• Turbo C is an Integrated Development Environment and compiler for the C programming language by Borland
  • Notably first introduced in 1987, the solution features comprehensive manuals, fast compile times, small size and low price

Turbo C General Structure

• Programs start with preprocessor directives
• #include gives access to libraries, inserting definitions from header files before compilation
  • #include<stdio.h> opens "stdio.h" for functions like scanf and `printf
• Every C program needs a main function where execution starts, name cannot be changed
• main function body is enclosed in braces {} comprised of declarations (memory cell names) and executable statements (derived from the algorithm).

Variable Declaration

• Important to consider how to allocate memory to handle data
• Variable declaration is a statement that communicates to the C compiler the names of all variables and the kind of informaiton stored
• Variables are declared before use in C
• Syntax: Data type variable list;
  • Example: int x, age;

Data Types

• Data Type is a set of values and operations on those values.
• Standard pre-defined data types include:
  • char
  • double
  • int
• Modifiers: they can be qualified by short, long, signed, or unsigned
  • short int <= int <= long int
  • float <= double <= long double
• Seven basic data types:
  • Text (char): single characters/strings, 1 byte, range 0-255
  • Integer
  • Floating-point
  • Double-floating point
  • Enumerated
  • void: signifies values that occupy 0 bit and have no value
  • Pointer: contains the address of the memory location

Defining Data Types

• int: integer numbers
  • Example: Int Count; Count = 5;
• float: floating point numbers
  • Example: float Miles; Miles = 5.6;
• double: BIG floating point numbers
  • Example: double Atoms, Atoms = 2500000;
• char: characters
  • Example: char Letter; Letter = 'x';

Variables

• Variable is a container in computer memory which stores, retrieves, and modifies values
• It is associated with a memory cell, whose value can change

Identifiers

• Identifier is the name that identifies or labels the identity of an object
• Key naming conventions:
  • Made up of letters and digits
  • Must start with a letter
  • C is case-sensitive
  • Underscore _ is considered as a letter
    • not recommended as the first character
  • First 3 characters of a name are significant
  • Should not be a reserved word/keyword in C

Fundamental Commands and Operators

• Equal sign (=): assignment operator, assigns the right value (rvalue) to the left variable (lvalue), example: lvalue = rvalue;
• Binary operators: arithmetic operators with two operands
  • +: adds
  • -: subtracts
  • *: multiplies
  • /: divides
  • %: computes remainder
• Address operator (&): returns the address of a variable
  • Important when getting an address in order to assign the data

Fundamental Input Command - scanf

• scanf() accepts data from standard input (keyboard), primarily for numeric data
• Syntax: scanf(“format specifier”, &var_name);
• The address operator returns the address of the variable to assign the data
• Assignment is done by position, separated with whitespace
• Format specifiers:
  • %Lf: Long double
  • %lf: Double
  • %f: Float
  • %lu: Unsigned long int
  • %ld: Long int
  • %u: Unsigned int
  • %d: Int
  • %hd: Short
  • %c: Char

Fundamental Output Command - printf

• printf() writes formatted output to the standard output (monitor) which can be a string, formatted value, or mixed expression
• Syntax:
  • printf(“string expression”);
  • printf(“format specifier”, var_name);
  • printf(“format specifier with string expression”, var_name);
• Format specifiers are the same as scanf()

Control Structure

• Control structure specifies the sequence of execution of a group of statements
  • namely sequential, conditional, and iterative.

Defining a Programming Problem

• Five steps for defining a programming problem:
  • Restate the problem
  • Analyze the problem
  • Identify the output
  • Identify the input
  • Identify the process.
• Variables should use descriptive names and appropriate data types.

C Language Elements: #define

• Directive define allows for text substitutions before compiling.
• Identifiers for preprocessor changes are in capital letters by convention.
  • Example: #define MAX 10 (MAX is a substitute of 10, every time MAX is stated, it means 10.)

Libraries

• Libraries are C implementations that contain collections of commonly used functions with the name ending in .h
• The #include call is used to open the file
  • Angle brackets <> for predefined, " " for user-defined

Comments

• C provides comments using multi-line remarks with /* */ and single-line with preceding slashes //
• Nested comments are not allowed
• Used to inform what code does and ignored by the compiler, thus not affecting program efficiency
• Can also be used to comment out sections of code when debugging

Reserved Words

• Reserved word is a word used in C language for a specific use and not to be used for anything else
• There is a complete list of 32 C reserved words

Punctuation Marks

• Character: Use
• /**/: enclose are single line remarks
• ”: display series of characters, and initializing string constant
• ;: statement separator
• ,: separate one variable to another
• =: assignment operator
• ': initializing character expresssion
• &: address operator
• {}: denotes the beginning and end of the program

Constants

• Constant identifiers have a constant value throughout program execution and written in uppercase letters by convention
• To create a read-only variable, use the keyword const keyword
  • Syntax: const float PI = 3.14
• Types of constants:
  • Character constants are put in single quotes
    • examles: 'A', '+'
  • Integer constants are numbers without fractional parts
    • Examples: 5 and -160
  • Floating constants require decimal points
    • Examples: 16.234, 4.23
  • String constants are sets of characters in double quotes
    • Examples: "bag", "this is good"
  • Backslash character constants are character constants in single quotes for most printing characters

Unary Operators

• Unary minus (-) or plus (+) changes the sign of a value/variable.

Increment (++) and Decrement (--) Operators

• ++: adds one to variable value
• --: subtracts one from variable value The value of the expression depends on where the operator is placed
  • Prefix increment is when the ++ is placed in front of its operand (value of expression is variable's value after increment)
  • Prefix decrement is when the -- is placed in front of its operand (value of expression is variable's value after decrement)
  • Postfix increment is when the ++ is placed immediately after the operand (value of expression is variable's value before increment)
  • Postfix decrement is when the -- is placed immediately after the operand (value of expression is variable's value before decrement)

Predefined Mathematical Functions

• The math.h library handles math functions, using double as an argument and returning a double
• Examples include: fabs() (absolute value), ceil() (rounds up), and floor() (rounds down), sqrt() (square root), pow() (power), and fmod() (remainder)

More I/O Functions

• Input/Output (I/O) functions in C:
  • getchar(): Reads a single character from the standard input.
    • Syntax: var_name = getchar();
  • getch(): Allows the user to input a character and wait for the enter key.
    • No echo is displayed, requires "conio.h"
    • Syntax: var_name = getch();
  • getche(): Allows the user to input a character and there is no need for the enter key
    • Inputted character will be echoed.
    • Syntax: var_name = getche();
  • gets(): Input a sequence of characters or string
    • gets(var_name);, where var_name is an array of characters.
  • puts(): Writes the string to the standard output device positions the cursor to the next line.
    • Syntax: puts(“string expression”);
  • putchar(): Writes a single character to the screen.
    • Syntax: putchar(var_name);
    • Also putchar(int); where the parameter may be a char variable of an integer value for a chatacter

Conditional Control Structure

• Conditional control structure evaluates condition with a true or false result, where false is 0 and true is any other non-zero value.
  • Utilizes the if statement with optional else or else-if
  • switch-case statement
• Conditional expressions or statements use these types of operators:
  • Relational operators: evaluate to true or false
    • Includes > (greater than), >= (greater than or equal to), < (less than), <= (less than or equal to), == (equal to), and != (not equal to)
  • Logical operators: logical “and”, “or” and “not”
    • && (and), || (or), and ! (not)
• Order of Precedence:
  • Arithmetic
    • *, /, %
    • +, -
  • Relational
    • <, <=, >, >=, ==, !=
  • Logical
    • !
    • &&
    • ||

if Statement

• Performs task when condition is true
• Syntax for single-if:

if (<conditional expression>)
    <statement>

• Example:

if(age > 18)
    printf("You are an adult!");

• For multiple statements, use a pair of braces:

if(age > 18){
    printf("You are an adult!");
    printf("Welcome to the club!");
}

• if-else (double alternatives):
  • if the condition is evaluated to true, then statementTrue is executed and statementfalse is skipped, otherwise it acts in reverse

if (<conditional expression>)
    <statementTrue>
else
    <statementFalse>

 - Example:

if(age > 18)
    printf("You are an adult!");
else
    printf("You are a minor!");

• if - else if - else (Multiple Alternatives) are evaluated in sequence until a true result is reached.

 if (<conditional expression>)
        <statement>
    else if (<conditional expression>)
        <statement>
    else
        <statement>

 - `Nested-if` is the placing an `if` statement inside an `if` statement

Switch Statement

• Switch statement compares a variable to a set of values (cases), which should be an int or char and made of case - constant

switch (<controlling expression>){
          case constant: <statement>
               break;
          case constant: <statement>
               break;
          default:
               <statement>
}

• Must use break to skip matching statements, otherwise the rest will be skipped