LectureNotes01142025

Lectures Notes -

Preconditions & PostConditions
- Frequently a programmer must comm precisely what a functin does, without any indication of how it works
- PreCondition - what must be true before the fuction is called
- PostCondition - statement indicates what is true after the functions performs its action

Double wingspan (bird) {
// Precondition: Pareameter must be abird
// Some invalid Preconditions: A different animal that does not have wings

}

Double sqrt( double x) {

// Precondition: x >= 0
// PostCondition 
}

sqrt(-10); does not meet precondition
sqrt(0); would meet the condition

Bool isVowel (char c) {

}

isVowel( '?');
// Nobody knows, because the precondition have been violated
// Violating the precondition might even crash the pc

-the programmer is resonsible fo rensuring that the precondition is valid when the function is called
- the pgorammer who writes the function couns on the precondition being valid, and ensures that the postcondition becomes true at the 
functions end

-- Example:

Evaluate the postfix expression: 4 5 6 * +

Step 1: Push 4 onto the stack.
Step 2: Push 5 onto the stack.
Step 3: Push 6 onto the stack.
Step 4: Encounter *:
Pop 6 and 5.
Compute 5 * 6 = 30.
Push 30 onto the stack.
Step 5: Encounter +:
Pop 30 and 4.
Compute 4 + 30 = 34.
Push 34 onto the stack.
The final result is 34.