第一题修改代码
很简单的 10进制转2进制，用的也是常规方法
附上考试时调出来的代码：
import java.util.*;
public class base
{
public static void main(String[] args)
{
int n,a,count0=0, count1=0;
String s="";
Scanner sc=new Scanner(System.in);
System.out.println("number");
n=sc.nextInt();
while(n>0){
a=n%2;
if(a==1){
count1++;
}else{
count0++;
}
n=n/2;
s=a+" "+s;
}
System.out.println("Bin number is "+s);
System.out.println("0count "+count0);
System.out.println("1count "+count1);
}
}
有些人的卷子上写的是
count1--;
需要改成
count1++;
另外在进制转时需要倒序排列数字，所以需要改成：
s=a+" "+s;
同时将语句将else里移出来，这题就调好了。
第二部分 选择题
Question 1
What are the values of a and b after the for loop finishes?
int a = 10;
int b = 3;
int t = 0;
for (int i = 1; i < 4; i++)
{
t = a;
a = i + b;
b = t - i;
}
(A) a = 5 and b = -2
(B) a = 6 and b = 7
(C) a = 6 and b = 3
(D) a = 12 and b = 1
(E) a = 5 and b = 8
简单推算即可，正确答案是E
Question 2
Consider the following code segment:
for(int i = 0; i <= 3; i++)
{
for(int j = 1; j <= 5; j+=2)
{
System.out.println("*");
}
}
How many times will a ‘*’ be printed?
(A) 3
(B) 6
(C) 9
(D) 12
(E) 15
此题正解为 $3 \times 4=12$。
但是有些人的卷子(本题第一行代码)上应该看到的是:
for(int i = 0; i <= 3; j++)
所以应该是存在语法错误，所以无法输出任何结果，故应填 No Answer!
Question 3
Consider the following code segment.
for (int k = 0; k < 20; k = k + 1)
{
if (k % 2 == 1)
System.out.print((k + 1) + " ");
}
What is printed as a result of executing the code segment?
(A) 1 3 5 7 9 11 13 15 17 19
(B) 0 2 4 6 8 10 12 14 16 18
(C) 2 4 6 8 10 12 14 16 18 20
(D) 3 6 9 12 15 18
(E) 0 2 4 6 8 10 13 14 16 18 20
此题通过if判断的k值应该为0-19之间的所有奇数，但是应为输出时输出的是
System.out.print((k+1)+" ");
所以应为 2-20的所有奇数
故选B
Question 4
Which of the following would be the correct result from the following expression?
123(Decimal) - 12(Octal) + 101(Binary) + D(Hex)
(A) 130 (Decimal)
(B) 133 (Decimal)
(C) 151 (Decimal)
(D) 132 (Decimal)
(E) 136 (Decimal)
此题依次转换为10进制即可
$123_{(10)}$ 无需转化，$12_{(8)}=1\times8^1+2=10_{(10)}$，$101_{(2)}=5_{(10)}$，$D_{(16)}=13_{(10)}$
最终转化成
$$123-10+5+13 = 131 $$
故无答案。
Question 5
Consider the following code segment:
int p = 5;
int q = 2;
int sum = 0;
while (p <= 8)
{
sum += p % q;
p++;
q++;
}
What is the value of sum after the code is executed?
(A) 1
(B) 0
(C) 13
(D) 7
(E) 4
这个也是比较简单的题，直接trace即可
最终答案sum = 7,故选D
Question 6
Consider the following code segment:
// int i = a random number such that 1 <= i <= n;
for (int a = 2; a <= i; a++)
for (int b = 1; b < i; b++)
System.out.println("*");
What is the minimum number of times that * will be printed?
(A) 0
(B) 1
(C) 2
(D) n - 1
(E) n - 2
此题定义i的取值范围 1<=i<=n 所以取i=1的时候，循环不执行，故输出0，应选A。
Question 7
Which of the following code will produce the following output?
1
22
333
4444
选项1：
for (int i = 1; i < 5; i++) {
for (int j = i; j > 0; j--) {
System.out.print(i+1);
}
System.out.println();
}
运行结果:
2
33
444
5555
选项2:
for (int i = 0; i < 5; i++) {
for (int j = 0; j < i; j++) {
System.out.print(i);
}
System.out.println();
}
运行结果:
1
22
333
4444
答案正确。
其他代码的运行结果就不进行列举了，鉴于选项顺序可能会有出入，这里列出所有错误的代码:
for (int i = 1; i < 5; i++) {
for (int j = i; j > 0; j--) {
System.out.print(i+1);
}
System.out.println();
}
for (int i = 1; i <= 5; i++) {
for (int j = i; j > 0; j--) {
System.out.print(i);
}
System.out.println();
}
for (int i = 1; i < 6; i++) {
for (int j = 0; j < i; j++) {
System.out.println(i);
}
}
for (int i = 0; i < 5; i++) {
for (int j = 0; j < i; j++) {
System.out.print(i+1);
}
System.out.println();
}
Question 8
When is the following Boolean expression true (a and b are integers)?
(a < b) && !(b > a)
(A) Always true (B) Never true (C) a = b (D) a < b (E) a > b
考虑两个情况, a<b 为 true和 a<b为false
根据 &&运算规则，有一个false就结果为false，所以never true
Question 9
Which of the following code segments is equivalent to the code below?
if (x >= 1) x = x * 3;
if (x > 3) x = 0;
(A) x = 0;
(B) if (x > 1) x = 0;
(C) if (x > 3) x = 0;
(D) if (x >=1) x = 0;
(E) none of the above
简单的不等式和代数转换之后可以得出，答案应为B
总结
这是本人目前根据psl上的题目得出的答案推算，最终结果请参考老师打分
如有疑问请在下方评论。