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loop_response = 'y';
while (loop_response == 'y'){
cout<<"\nWhat is your age? ";
cin>>age_user;
cout<<"\nWhat is your friend's age? ";
cin>>age_friend;
cout>>"\nTogether your ages add up to: ";cout>>(age_user + age_friend);
cout<<"\nDo you want to do it again? y or n ";
cin>>loop_response;
}
The four attributes of a test before loop are present. The initialization of the flag. The test is the equality relational comparison of the value in the flag variable to the lower case character of y. The action part consists of the 6 lines that prompt for data and then displays the total of the two ages. The update of the flag is the displaying the question and getting the answer for the variable loop_response.
This type of loop control is called an event controlled loop. The flag updating is an event where someone decides if they want the loop to execute again.
Using indentation with the alignment of the loop actions and flag update is normal industry practice within the C++ community.
At this point it's worth mentioning that good programming always provides for a method to insure that the loop question will eventually be false so that the loop will stop executing and the program continues with the next line of code. However, if this does not happen then the program is in an infinite loop. Infinite loops are a bad thing. Consider the following code:
loop_response = 'y';
while (loop_response == 'y'){
cout<<"\nWhat is your age? ";
cin>>age_user;
cout<<"\nWhat is your friend's age? ";
cin>>age_friend;
cout>>"\nTogether your ages add up to: ";
cout>>(age_user + age_friend);
}
The programmer assigned a value to the flag before the loop which is correct. However, he forgot to update the flag. Every time the test expression is asked it will always be true. Thus, an infinite loop because the programmer did not provide a way to exit the loop (he forgot to update the flag). Consider the following code:
loop_response = 'y';
while (loop_response = 'y'){
cout<<"\nWhat is your age? ";
cin>>age_user;
cout<<"\nWhat is your friend's age? ";
cin>>age_friend;
cout>>"\nTogether your ages add up to: ";
cout>>(age_user + age_friend);
cout<<"\nDo you want to do it again? y or n ";
cin>>loop_response;
}
No matter what the user replies during the flag update, the test expression does not do a relational comparison but does an assignment. It assigns 'y' to the variable and asks if 'y' is true? Since all non-zero values are treated as representing true within the Boolean concepts of the C++ programming language, the answer to the test expression is true. Viola, you have an infinite loop.
loop_response = 'y';
while (loop_response == 'y');{
cout<<"\nWhat is your age? ";
cin>>age_user;
cout<<"\nWhat is your friend's age? ";
cin>>age_friend;
cout>>"\nTogether your ages add up to: ";
cout>>(age_user + age_friend);
cout<<"\nDo you want to do it again? y or n ";
cin>>loop_response;
}
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