Question

Programming languages question (Please help if you can)

Prove (or disprove) that the following pre-post form is correct

{ x > 0 }

if (x > 0)

y = 2 * x + 1;

else

y = x + 4;

{ y < 3 }

Answer 1

In above problem there is two condition :-
pre condition :- x > 0 /* it means that given input which will be x and x>0.*/
post condition :- y < 3 /* after program will finish it's execution if it is correct then it will meet the condition */

{ x > 0 }
if(x>0)
y=2*x+1;
else
y=x+4;
{ y < 3 }

-> in above example we will give some input and check wether the program is correct or not.
input :- 1 (x=1>0)
output :- 3 (y=3!<3)

here we give input (1) which satisfy the pre condition then y will become 3 which will not satisfy post condition. so, we can say that this problem is not correct. so it is disproved that above form is correct.