双语版c++ 第四章答案

Chapter Four Selection and Iteration

Exercises

1. Rewrite the following if-else using a switch statement:

if ( marriage_status == 'S' )

cout << "single" ;

else if ( marriage_status == 'M' )

cout << "married" ;

else if ( marriage_status == 'W' )

cout << "widowed" ;

else if ( marriage_status == 'E' )

cout << "separated" ;

else if ( marriage_status == 'D' )

cout << "divorced" ;

else

cout << "error: invalid code" ;

解答：

switch (marriage_status)

{

case ‘S’:

cout << "single" ;

break;

case ‘M’:

cout << "married" ;

break;

case ‘W’:

cout << "widowed" ;

break;

case ‘E’:

cout << "separated" ;

break;

case ‘D’:

cout << "divorced" ;

break;

default:

cout << "error: invalid code" ;

}

2. The following program segment displays an appropriate message depending on the values of three integers: n1, n2, and n

3.

if ( n1== n2 )

if (n1 == n3 )

cout << "n1, n2 and n3 have the same value" << endl ;

else

cout << "n1 and n2 have the same value" << endl ;

else if ( n1 == n3 )

cout << "n1 and n3 have the same value" << endl ;

else if ( n2 == n3 )

cout << "n2 and n3 have the same value" << endl ;

else

cout << "n1, n2 and n3 have different values" << endl ;

Use spaces to improve the readability of this code.

To test the various branches in this code you will need to construct five sets of test data, each set testing one of the branches. Construct the five sets of test data for n1, n2, and n3.

解答：

/*测试用例为：1 1 1 ，1 1 2 ，1 2 1 ，1 2 2 ，1 2 3*/

#include

using namespace std;

int main(){

int n1,n2,n3;

cin>>n1>>n2>>n3;

if(n1==n2)

if(n1==n3)

cout<<"n1,n2 and n3 have the same value"<

else

cout<<"n1 and n2 have the same value"<

else if(n1==n3)

cout<<"n1 and n3 have the same value"<

else if(n2==n3)

cout<<"n2 and n3 have the same value"<

else

cout<<"n1,n2 and n3 have the different value"<

return 0;

}

3. Write a program to read in two integers and check if the first integer is evenly divisible by the second. (Hint: use the modulus operator %.)

解答：

#include

using namespace std;

int main(){

int n1,n2;

cout<<"please input the two numbers:";

cin>>n1>>n2;

if(n1%n2==0)

cout<

else

cout<

return 0;

}

4. Input two numbers and find the smaller of the two using the conditional operator ?:.

解答：

#include

using namespace std;

int main(){

int n1,n2;

int smaller;

cout<<"please input the two numbers:";

cin>>n1>>n2;

if(n1!=n2){

smaller=(n1

cout<<"the smaller one is "<

}else

cout<<"n1=n2"<

return 0;

}

5. In a triangle, the sum of any two sides must be greater than the third side. （triangle：三角形）Write a program to input three numbers and determine if they form a valid triangle.

解答：

#include

using namespace std;

int main(){

double a ,b ,c;

cout<<"please input the three sides of a triangle:";

cin>>a>>b>>c;

if(((a+b)>c)&&((a+c)>b)&&((c+b)>a)){

cout<<"the three number can form a valid triangle."<

return 0;

}

cout<<"the three number can not form a valid triangle."<

return 0;

}

6. Input a person’s height in centimetres and weight in kilograms and display a message indicating that they are either underweight, overweight or normal weight. As an approximation, a person is underweight if their weight is less than their height divided by 2.5 and they are overweight if their weight is greater than their height divided by 2.3.

解答：

#include

using namespace std;

int main(){

double height,weight;

cout<<"please input your height in centimetres and weight in kilograms:";

cin>>height>>weight;

if(weight

cout<<"underweight!"<

else if(weight

cout<<"normal weight!"<

else

cout<<"overweight"<

return 0;

}

7. Write a program that reads a single numeral from the keyboard and displays its value as a word. For example, an input of 5 will display the word ‘five’.

解答：

#include

using namespace std;

int main(){

int num;

cout<<"please input a single numeral:";

cin>>num;

switch(num){

case 0:cout<<"zero"<

case 1:cout<<"one"<

case 2:cout<<"two"<

case 3:cout<<"three"<

case 4:cout<<"four"<

case 5:cout<<"five"<

case 6:cout<<"six"<

case 7:cout<<"seven"<

case 8:cout<<"eight"<

case 9:cout<<"nine"<

default: cout<<"please input a single numbera l"<

}

return 0;

}

8. Write a program to input a number 1 to 7 from the keyboard, where 1 represents Sunday, 2 Monday, 3 Tuesday, etc. Display the day of the week corresponding to the number typed by the user. If the user types a number outside the range 1 to 7, display an error message.

解答：

#include

using namespace std;

int main(){

int theday;

cin>>theday;

int flag=1;

while(flag){

switch(theday){

case 1:cout<<"sunday"<

case 2:cout<<"monday"<

case 3:cout<<"tuesday"<

case 4:cout<<"wednesday"<

case 5:cout<<"thursday"<

case 6:cout<<"friday"<

case 7:cout<<"saturday"<

default: cout<<"error.please input a number between 1-7";cin>>theday;

}

}

return 0;

}

9. Add the increment operator (I or i) and the decrement operator (D or d) to the simple calculator program P4D.

解答：

#include

using namespace std;

int main(){

double a,b;

double result;

char opt;

cout<<"please input like :1 i 3 or 1 d 3 "<

cin>>a>>opt>>b;

if(opt=='i'||opt=='I')

result=a+b;

else if(opt=='d'||opt=='D')

result=a-b;

else

cout<<"input error!"<

cout<<"the result is "<

return 0;

}

10. Write a program to input the time of day in Ireland and display the equivalent time in Washington (- 5 hours), Moscow (+ 3 hours), and Beijing (+ 8 hours). Input the time in th e 24-hour format, e.g. 22:35 (11:35 p.m.).

解答：

#include

int main(){

int hour,minute;

int h;

printf("please input the time of day in Ireland in 24-hour format ");

scanf("%d:%d",&hour,&minute);

if(hour>=0&&hour<=23&&minute>=0&&minute<=59){

if((h=hour-5)<0) h+=24;

printf("the equivalent time in Washington is %d:%d ,in Moscow is %d:%d ,in Beijing is %d:%d .",h,minute,(hour+3)%24,minute,(hour+8)%24,minute);

}

else

printf("error input!");

return 0;

}

11. Write a program to display the effects of an earthquake based on the Richter scale value:

Richter scale value Effects

Less than 4 Little.

4.0 to 4.9 Windows shake.

5.0 to 5.9 Walls crack; poorly built buildings are damaged.

6.0 to 6.9 Chimneys tumble; ordinary buildings are damaged.

7.0 to 7.9 Underground pipes break; well-built buildings are damaged.

More than 7.9 Ground rises and falls in waves; most buildings are destroyed. （Richter scale value：里氏震级）

解答：

#include

int main(){

float rsvalue;

cin>>rsvalue;

if(rsvalue>0){

int value=rsvalue;

switch(value){

case 1:;

case 2:;

case 3:cout<<"Little effects!"<

case 4:cout<<"Windows shake!"<

case 5:cout<<"Walls crack;poorly built buidings are damaged!"<

case 6:cout<<"Chimneys tumble;ordinary buidings are damaged!"<

case 7:cout<<"Underground pipes break;well-buildings are damaged!"<

default:cout<<"Ground rises and falls in waves;most buildings are destroyed!"<

}

}else

cout<<"error input!"<

return 0;

}

12. What is the output from the following?

for ( int j = 1, int i = 10 ; i > 0 ; i /= 2, j++ )

cout << i << j ;

解答：

输出：101522314

13. Modify program P4F to calculate the average along with the total of the numbers entered. 解答：

#include

using namespace std;

int main(){

double a,b;

double result;

char opt;

int num=0;

double sum=0;

double ave=0.0;

while(1){

cout<<"please input like :1 i 3 or 1 d 3 "<

cin>>a>>opt>>b;

num+=2;sum+=(a+b);

if(opt=='i'||opt=='I')

result=a+b;

else if(opt=='d'||opt=='D')

result=a-b;

else

cout<<"input error!"<

ave=sum/num;

cout<<"the result is "<

cout<<"the average along with the total of the numbers entered is "<

}

return 0;

}

14. Rewrite the following using a for loop.

int i = 0, total = 0 ;

while ( i < 10 )

{

cin >> n ;

total += n ;

i++ ;

}

解答：

#include

int main(){

int i=0,total=0;

int n;

loop:cin>>n;

total+=n;

i++;

if(i<10) goto loop;

cout<

return 0;

}

15. What is displayed when the following program is run and the number 1234 is entered?

int num ;

cout << "Please enter a number " ;

cin >> num ;

do

{

cout << num % 10 ;

num /= 10 ;

}

while ( num != 0 ) ;

解答：当输入为1234时，输出为4321

16. The following program segment is intended to compute 0.1 + 0.2 + 0.3 ... + 99.8 + 99.9. It contains

a flaw. What is it, and how would you correct it?

float sum = 0.0 ;

float i = 0.1 ;

while ( i != 100.0 )

{

sum += i ;

i += 0.1 ;

}

解答：

#include

int main(){

double sum=0.0;

double i=0.1;

int j=1;

while(j<=999){

sum+=i;

i+=0.1;

j++;

cout<

return 0;

}

17. What is the output from the following?

(a)

for (int i = 0 ; i < 5 ; i++ )

for ( int j = i ; j < 5 ; j++ )

cout << i << j << en dl ;

(b)

for ( int i = 0 ; i < 5 ; i++ )

for ( int j = 0 ; j < 5-i ; j++ )

cout << i << j << en dl ;

解答：

（a）输出为：00，01，02，03，04，11，12，13，14，22，23，24，33，34，44 （b）输出为：00,01,02,03,04,10,11,12,13,20,21,22,30,31,40

18. Write a for loop to

(a) display the numbers 0, 5, 10, 15, ..., 100

(b) display the numbers 1, 2, 4, 8, 16, ..., 1024.

解答：

（a）

#include

int main(){

for(int i=0;i<=100;i+=5)

{

cout<

}

return 0;

}

（b）

#include

int main(){

int sum=1;

for(int i=1;i<=11;i++)

{

cout<

sum*=2;

}

return 0;

}

19. Write a program to find the sum of all the odd integers in the range 1 to 99.

#include

#include

int main(){

int sum=0;

for(int i=1;i<=99;i+=2){

sum+=i;

}

cout<

return 0;

}

20. Write a program that outputs all the numbers from 5 and 50 that are divisible by 3 or 5.

解答：

#include

#include

int main(){

for(int i=5;i<=50;i++)

if(i%3==0||i%5==0)

cout<

return 0;

}

21. Write a program to display all the hour and minute values in a 24-hour clock, i.e. 0:00 0:01 ... 23:59. How would you display the values in fifteen-minute intervals?

解答：

#include

#include

int main(){

for(int h=0;h<=23;h++)

for(int m=0;m<=59;m++)

if(m<10)

cout<

else

cout<

return 0;

}

22. Write a program to display the following triangles:

*

**

***

****

*

***

****

Input the size of the triangles from the keyboard.

解答：

#include

#include

int main(){

int i,j,k;

for(i=1;i<=4;i++){

for(j=1;j<=i;j++)

cout<<"*";

cout<

}

for(i=1;i<=4;i++){

for(j=1;j<=(4-i);j++)

cout<<" ";

for(k=1;k<=i;k++)

cout<<"*";

cout<

}

return 0;

}

23. Write a program that lets a teacher enter the percentage marks for a class. The teacher enters a negative mark to indicate that there are no more marks to be entered. Once all the marks have been entered, the program displays the average mark for the class. （negative mark：负数标记）

解答：

#include

int main(){

float mark;

float sum=0.0;

float ave;

int num=0;

cin>>mark;

while(mark>=0)

{

sum+=mark;

num++;

cin>>mark;

}

ave=sum/num;

cout<

return 0;