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Introduction to C Programming
Overview of C
C is an imperative procedural language that supports structured programming, lexical variable scope, recursion, and uses a static type system.
Evolution of C
The ancestor of C was called B in 1971. The first version of C was created by Kernighan and Ritchie in 1972. The C99 version, introduced in 1999, allows mixed declarations and executables, variable length arrays, and new types supporting Unicode characters, complex numbers, and boolean values.
Preprocessor Directives
A preprocessor is a system program that modifies the C program before compilation. A preprocessor directive is an instruction to the preprocessor. A library is a collection of functions, symbols, and values. Two types of preprocessor directives exist: #include, used to include libraries of functions and macro values. #include <stdio.h> includes the standard input/output header, which contains macro definitions, constants, and declarations of functions and types for standard input and output operations.
Comments in C
Comments are lines of code that are ignored by the compiler.
Instructions
Instructions, also known as statements, are terminated by a semicolon (;). Line changes and tabs are not significant to the C compiler. For example, a=3; b=4; c=5; is equivalent to a = 3; b = 4; c = 5;.
Skeleton of a Program
A basic C program structure includes #include <stdio.h>, additional includes, constant macros, the int main (void) function containing declarative and executable statements, and return (0);.
My First Program
A simple C program includes the stdio.h header, the main function, a printf statement to display output, and a return (0); statement. The return (0); statement returns an integer (0) to the operating system,
indicating successful program completion. It is typically the last statement in a program.
Variables
In programming, variables are used to store data. C has three basic types of variables.
Basic Data Types
int represents a whole number.
Identifiers
All variables must be declared and have names. Examples include int lifespan;, double mass;, and char letter;.
Hard Rules for Identifiers
An identifier must not be a reserved word. An identifier must never begin with a digit. An identifier should not be a standard identifier. Examples of valid and invalid identifiers are provided.
Executable Statements
Executable statements should come after the declarations in a function for compatibility with all compilers.
Assignment Statements
An assignment statement copies the value on the right-hand side of the = operator to the variable on the left-hand side. For example: kms = KMS_PER_MILE * miles;. Assignment is not the same as an algebraic equation. For example, sum = sum + item; is a valid assignment. The right side of an assignment can be a constant, a variable, or an expression.
The printf Statement
The printf statement displays a line of program output. It uses a print list, which contains the variables or expressions whose values are displayed. Placeholders, symbols beginning with % in a format string, indicate where to display the output value. For example: printf ('That equals %lf kilometers. \n', kms);.
Placeholders in Format String
%c is used for char variables in printf and scanf.
Arithmetic Operators
The arithmetic operators in C include + (addition), - (subtraction), * (multiplication), / (division), and % (remainder). Integer expressions always return integer results. For example, 5 + 2 is 7 , 5.0 + 2.0 is 7.0, 5 - 2 is 3 , 5.0 - 2.0 is 3.0, 5 * 2 is 10 , 5.0 * 2.0 is 10.0, 5.0 / 2. is 2.5, 5 / 2 is 2 , and 5 % 2 is 1.
Integer Division
An operation with two integer operands always gives an integer answer.
Expressions with Multiple Operators
A unary operator is an operator with one operand. For example: x = y + z;.
Rules for Evaluating Expressions
Rule #1: Parentheses Rule - All sub-expressions are evaluated separately. Rule #2: Operator Precedence Rule - unary + - first, * / % next, binary + - last. Rule #3: Associativity Rule - Right Associativity: Unary operators in the same expression and at the same precedence level are evaluated right to left.
Numerical Inaccuracies
Representational error is an error due to coding a real number as a finite number of binary digits. Arithmetic underflow is an error in which a very small computational result is represented as zero.
Modes of Operation
Interactive mode involves the user responding to prompts by typing in data.
Reading from an Existing File
To read from a file, you need first to declare it (FILE is all uppercase). fclose (in);
Writing/Creating a New File
To create a new file and write into it from a file, you need first to declare it. fclose (out);
Common Programming Errors
Syntax errors are violations of the C grammar rules.
