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Assignment 2

# Assignment 2 - {true x:=1{x=2 i{x>x x:=5{x=6 j{y=5...

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CS536 Science of Programming Assignment #2 Spring 2010 Due date – Feb. 05, 2010 2PM. 1. Consider the following program. (15 points) ---------------------- {a≥0 and b≥0} x:=a; y:=b; { } while x≠y loop { } if x>y the x:=x-y else y:=y-x; { } end; g:=x; { } {g=gcd (a,b)} ---------------------- Where gcd(a,b) means the greatest common devisor of a and b Above program may be correct, partially correct or incorrect. Do following : If you think this program is incorrect with respect to its specification – show it. If you think the program is partially correct or totally correct with respect to its specification then add partial correctness assertions. 2. For the following assignment programs prove correctness or show incorrect. (20 points) a. { x + y = z } x := y { 2y = z } b. { x = 2 } x := 2 * x + 1 { odd(x) } c. { true } x := 3 { x = 3 } d. { true } x := 3 { odd(x) } e. { false } x := 0 { x = 1 } f. {even(x+y)} x := 5x-3y {even(x+y)} g. {true} x:=y {x≤ y} h.

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Unformatted text preview: {true} x:=1 {x=2} i. {x>x} x:=5 {x=6} j. {y=5} x:=5 {y=5 ^ x>y} 3. Compute following (8 points) a. wp( x:=2x+3, x=13) b. wp (x:=x+y, x < 2y) c. wp (x:=y*c, x*y = c) d. wp( x:= (x-y)*(x+y) , x+y*y ≠0) 4. For the following assignment programs prove correctness or show incorrect. ( 20 points) a. { z = 3 } x:=1 ; y:=2 { x + y ≤ z } b. { z < 3 } x:=1 ; y:=2 { x + y < z } c. { x ≠ y } x:=y ; y:=x{ x = y } d. { x = 0 } x:=5 ; x:=5 { x ≤ y } e. { y = z } x:=z; y:= z+2 { x = z } f. { true } x:=x+1; y:=x+1 { x = y } g. { x = 1 ^ y = 1 } x:=2y ; y:= 2x { x = y } h. {false} x:=2 ; y:=3 {y>x} i. {true} x:=2 ; y:=3 {y>x} j. {false} x:=1 ; x:=2 {false} 5. Compute following (12 pts) a. wp (x:=y;y:=x , x=y) b. wp (x:=x+1;y:=y+1 , x>y) c. wp (x:=y+1;y:=x+1 , x<y) d. wp( x := 2x+y -5;y:= 2x , y<100) e. wp ( x:=y; y:=z;z:=y;x:=z, even(x) ) f. wp ( x:=2y; x:= x+3k, x<z) 6. prove P => wp (S.R) {P} S {R}...
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