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CSE143X Sample Assertions Problems handout #4
1. Assertions. You will identify various assertions as being either always
true, never true or sometimes true/sometimes false at various points in
program execution. The comments in the method below indicate the points
of interest.
// pre: y > 0
public static void mystery(int x, int y) {
int z = 0;
// Point A
while (x >= y) {
// Point B
x = x - y;
// Point C
z++;
// Point D
}
// Point E
System.out.println(z + " " + x);
}
Fill in the table below with the words ALWAYS, NEVER or SOMETIMES.
x < y x == y z == 0
+---------------------+---------------------+---------------------+
Point A | | | |
+---------------------+---------------------+---------------------+
Point B | | | |
+---------------------+---------------------+---------------------+
Point C | | | |
+---------------------+---------------------+---------------------+
Point D | | | |
+---------------------+---------------------+---------------------+
Point E | | | |
+---------------------+---------------------+---------------------+
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2. Assertions. You will identify various assertions as being either always
true, never true or sometimes true/sometimes false at various points in
program execution. The comments in the method below indicate the points
of interest.
// pre : y >= 0
// post: returns x^y
public static int pow(int x, int y) {
int prod = 1;
// Point A
while (y > 0) {
// Point B
if (y % 2 == 0) {
// Point C
x = x * x;
y = y / 2;
// Point D
} else {
// Point E
prod = prod * x;
y--;
// Point F
}
// Point G
}
// Point H
return prod;
}
Assume the method is called only if the precondition is true. Fill in the
table below with the words ALWAYS, NEVER or SOMETIMES.
y == 0 y % 2 == 0
+---------------------+---------------------+
Point A | | |
+---------------------+---------------------+
Point B | | |
+---------------------+---------------------+
Point C | | |
+---------------------+---------------------+
Point D | | |
+---------------------+---------------------+
Point E | | |
+---------------------+---------------------+
Point F | | |
+---------------------+---------------------+
Point G | | |
+---------------------+---------------------+
Point H | | |
+---------------------+---------------------+
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Solution to CSE143X Sample Assertions Problems
1. x < y x == y z == 0
+---------------------+---------------------+---------------------+
Point A | sometimes | sometimes | always |
+---------------------+---------------------+---------------------+
Point B | never | sometimes | sometimes |
+---------------------+---------------------+---------------------+
Point C | sometimes | sometimes | sometimes |
+---------------------+---------------------+---------------------+
Point D | sometimes | sometimes | never |
+---------------------+---------------------+---------------------+
Point E | always | never | sometimes |
+---------------------+---------------------+---------------------+
2. y == 0 y % 2 == 0
+---------------------+---------------------+
Point A | sometimes | sometimes |
+---------------------+---------------------+
Point B | never | sometimes |
+---------------------+---------------------+
Point C | never | always |
+---------------------+---------------------+
Point D | never | sometimes |
+---------------------+---------------------+
Point E | never | never |
+---------------------+---------------------+
Point F | sometimes | always |
+---------------------+---------------------+
Point G | sometimes | sometimes |
+---------------------+---------------------+
Point H | always | always |
+---------------------+---------------------+
]]>