java第三章课后习题答案

3-1

import java.util.*;

public class XIN31{

public static void main(String args[]){ double sum;

Scanner reader=new Scanner(System.in); System.out.println("请输入一个值:"); double x=reader.nextDouble(); if(x<=0)

{

sum=2*x-1;

System.out.println("y="+sum); }

{

}

System.out.println("y="+sum); }

}

3-2

public class XIN32{ sum=3*x-1; else

public static void main(String args[]){ int sum=0,j;

int i=1;

while(i<=1000)

{

j=i%(7*3);

if(j==0)

{

sum=sum+i;

i++;

}

else

i++;

}

System.out.println("数值="+sum); }

}

3-3

import java.util.*;

public class XIN33

{

public static void main(String args[])

} { } int i = 0, a = 8, sum = 8; for (i = 1; i <= 9; i++) { } System.out.println("数值=" + sum); a = a * 10 + 8; sum = sum + a;

3-4

public class XIN34{

public static void main(String args[]){ int sign=-1;

double deno=1.0,term,sum=0.0; while(deno<=19999)

{

sign=-sign;

term=sign/deno;

sum=term+sum;

deno=deno+2;

}

System.out.println("结果为="+sum); }

}

3-5

import java.util.*;

public class XIN35

{

public static void main(String args[]) { int i = 0, sum = 0, sum1 = 0, sum2 = 0; int j = 0, a, b, c; for (i = 0; i <= 199; i++) { } for (j = 0; j <= 99; j++) { b = j * (j - 1); b = b * (j + 1); sum2 = sum + b; a = i * (i - 1); a = a * (i + 1); sum1 = sum + a;

} } } c = sum1 - sum2; System.out.println("结果为" + c);