Overview of C

C Programming language

Imperative procedural language. 80

Process

flowchart TD
	editor(editor) --> source[source code] --> compiler(compiler) --> object[object code] --> linker(linker) --> executable[executable code]
	otherobject[other object codes] --> linker
	function[function libraries] --> linker

An example of a compiler is gcc.

To display all details: gcc -v HelloWorld.c

• Preprocessing
• Compilation
• Assembler
• Linker

Abstraction

flowchart TD
	high["High level language program (C)"] ---|compiler| assembly["Assembly language program (MIPS)"]
	assembly ---|assembler| machine["Machine Language Program (MIPS)"]
	machine ---|machine interpretation| hardware["Hardware Architecture Description (Logic, Logisim)"]
	hardware ---|architecture implementation| logic["Logic Circuit Description (Logisim)"]

Computation

Function

A function body has two parts: Declaration statement: What type of memory cells needed Executable statement: Describe processing on memory cells

Declaration statement

int count

User defined identifier - name of variable of function.

• Must not begin with a digit, but can contain letters, digits and underscores
• Case sensitive
• Guideline: start with lowercase letter

Reserved words int, void, double, return etc Standard identifiers printf, scanf etc

Executable statement

printf, scanf Computational and assignment statements

lvalue = assigned value Stores a value or a computational result in a variable. lvalue must be assignable. Assignment can be cascaded, with associativity from right to left: b = (c = 3 + 6)

Side-effect An assignment statement also returns the value of the right-hand side.

Arithmetic operations

Precedence rule

1. Primary expression operators (Left to right)
   • () expr++ expr --
2. Unary operators (Right to left)
   • * & + - ++expr --expr (typecast)
3. Binary operators
   • * / %
   • + -
4. Ternary operator
   • ? :
5. Assignment operators
   • = += -= *= /= %=

Execution:

• Left to right
• Parenthesis rule
• Precedence rule
• Associative rule
• Truncation (if result can be stored)
  • int n; n = 9 * 0.5 results in 4 being stored in n

Typecasting

Uses a cast operator to change the type of an expression int aa = 10; float pp = (float) aa / 4;

Modulo vs Remainder

Python % is a modulo, while C’s % is a remainder. This results in a different value for negative values.

In Python:

a = 10 % 4  # a = 2
b = -10 % 4 # b = 2

In C:

a = 10 % 4  // a = 2
b = -10 % 4 // b = -2

Selection Structures

There are two selection structures:

if () {
	
}
elif () {
 
}
else {
 
}

switch () {
	case x:
		...
		break;
	case y:
		...
		break;
	default:
		...
		break;
}

Relational Operators < <= > >= == != Truth Values true false - false is represented as 0, and any other value can represent true Logical Operators && || !

Short-circuit evaluation

For AND statements expr1 && expr2

Short-circuit evaluation expr1 is false, skip evaluating expr2 and return false immediately

if

For OR statements expr1 || expr2

Short-circuit evaluation expr1 is true, skip evaluating expr2 and return true immediately

if

Repetition

while ()
{
 
}

do {
 
} while ()

for (initalization; condition; update) {
 
}

break only breaks out of the inner-most loop containing the statement in a nested loop. Similarly, continue skips to the next iteration of the inner-most loop containing the statement in a nested loop