C++ Primer Plus Chapter 6 Exercise 2 Enter understanding - c++

Question

I am learning from C++ Primer Plus book, and I've recently done this exercise from the book. I have a problem: when the user hits enter without any sign, then in the next entry to display any of these functions he has to hit enter again, because if not it'll still display "Wrong choice" and "Next Choice:" all the time. Can you tell me what's wrong with this code, and what should I add?
Thanks in advance.
/*When you join the Benevolent Order of Programmers, you can be known at BOP
meetings by your real name, your job title, or your secret BOP name.Write a program
that can list members by real name, by job title, by secret name, or by a member’s
preference. Base the program on the following structure:
// Benevolent Order of Programmers name structure
struct bop {
char fullname[strsize]; // real name
char title[strsize]; // job title
char bopname[strsize]; // secret BOP name
int preference; // 0 = fullname, 1 = title, 2 = bopname
};
In the program, create a small array of such structures and initialize it to suitable
values. Have the program run a loop that lets the user select from different alternatives:
a. display by name b. display by title
c. display by bopname d. display by preference
q. quit
302 Chapter 6 Branching Statements and Logical Operators
Note that “display by preference” does not mean display the preference member; it
means display the member corresponding to the preference number. For instance, if
preference is 1, choice d would display the programmer’s job title.A sample run
may look something like the following:
Benevolent Order of Programmers Report
a. display by name b. display by title
c. display by bopname d. display by preference
q. quit
Enter your choice: a
Wimp Macho
Raki Rhodes
Celia Laiter
Hoppy Hipman
Pat Hand
Next choice: d
Wimp Macho
Junior Programmer
MIPS
Analyst Trainee
LOOPY
Next choice: q
Bye!*/
Solution:
#include <iostream>
void text();
void name();
void title();
void secret();
void prefr();
const int strSize = 23;
const int People = 4;
char ch;
struct bop {
char fullname[strSize]; // real name
char title[strSize]; // job title
char bopname[strSize]; //secret BOP name
int preference; // 0 = fullname, 1 = title, 2 = bopname
};
bop people[People] //array of 4 structures
{
{"Tony Hawk", "Junior Programmer", "Novice",2}, //first member
{"Bill Gates", "Founder of Microsoft", "Billionaire",1}, //second member
{"Pop Leather", "Graphic Designer", "Fast and Furious",2}, //third member
{"Steve Jobs", "Apple Leader", "Undead Dragon",0} //fourth member
};
int main()
{
text(); //call a text function
std::cin.get(ch); //get a character
int i=0;
while(ch!='q')
{
switch(ch)
{
case 'a':
name();
break;
case 'b':
title();
break;
case 'c':
secret();
break;
case 'd':
prefr();
break;
default: std::cout << "Wrong choice\n";
}
std::cout << "Next choice: \n";
std::cin.get();
std::cin.get(ch);
}
std::cout<<"Bye!";
return 0;
}
void text()
{
std::cout<<"Benevolent Order of Programmers Report\n"
"a. display by name b. display by title\n"
"c. display by bopname d. display by preference\n"
"q. quit\n"
"Enter your choice:";
}
void name()
{
for(int i=0;i<People;i++)
std::cout<<people[i].fullname<<std::endl;
}
void title()
{
for(int i=0;i<People;i++)
std::cout<<people[i].title<<std::endl;
}
void secret()
{
for(int i=0;i<People;i++)
std::cout<<people[i].bopname<<std::endl;
}
void prefr()
{
for(int i=0;i<People;i++)
{
if(people[i].preference==0)
std::cout<<people[i].fullname<<std::endl;
else if(people[i].preference==1)
std::cout<<people[i].title<<std::endl;
else if(people[i].preference==2)
std::cout<<people[i].bopname<<std::endl;
}
}

Answer 1

I think the problem lies here:
std::cin.get();
std::cin.get(ch);
If there was indeed a character, the first get will clean the newline, and the second will perform another read.
If there was no character to begin with, the first get will consume the actual input, and ch end up as a newline.
A solution to that is: don't treat input as valid if you're not sure it's valid. In particular, you're expecting two characters of input: any character except newline followed by newline.
There are two rather simple ways to solve your problem:
Don't use characters: simply work on std::string and treat empty string as invalid.
Check if the first character was a newline and don't skip an additional character then.
A more advanced solution would be to experiment more with functions. Could you wrap the input to return optional<char>? Or even better, optional<Choice>, where Choice is an enum class?
Or perhaps you could create a function that loops automatically, prompting for a proper input every time, and separate it from the main program logic?