C++ Loop for String

Question

I am struggling to create a loop for getting input from user. The input must push_back() each instance.

#include <iostream>
#include <array>
#include <cstring>
#include <vector>
#include <string>
#include <string.h>
using namespace std; 

int main()
{
    vector <string> bookQ = { "what","book","is","that","you","are","reading" };
    for (int i = 0; i < bookQ.size(); i++) {
        cout << bookQ[i] << ' ';        
    }
    cout << endl;
    string input;
    int x = 0;    
    for (x != '1') {                                 // require a loop to input string and  end when user prompts                      
        cout << "Enter 1 to stop" << endl;           //
        cin >> x;                                    //
        getline(cin, input);                         //
        bookQ.push_back(input);                      //
    }                                                //
    for (int i = 0; i < bookQ.size(); i++) {
        cout << bookQ[i] << ' ';
    }
    cout << endl;
    return 0;
}

whats wrong with the code? Please include example input, output and expected output in the question — 463035818_is_not_an_ai, Jul 03 '22 at 19:45
On your input loop you're using `for (x != '1')`. That should probably be a `while` instead of `for`. — jkb, Jul 03 '22 at 19:49
Error occurs at the loop // (x != '1') " ! <- "not declared and states ";" needs to be added — Hendrik, Jul 03 '22 at 19:49
Problem with while loop: Output just runs after any input without end... want the user to input eg. "my book c++" but as "my" then "book" then "c++" and user finished then ends loop — Hendrik, Jul 03 '22 at 19:54
@Hendrik Did any of the answers help? If you haven't read it, this is good: [What should I do when someone answers my question?](https://stackoverflow.com/help/someone-answers) — Ted Lyngmo, Jul 08 '22 at 00:16

score 2 · Accepted Answer · answered Jul 03 '22 at 20:00

Your for loop is missing the declaration and (iteration) expression parts:

for (declaration-or-expression; declaration-or-expression; expression)

so it should have looked like this:

for (;x != '1';) {

which is generally written as

while (x != '1') {

That would cause problems though since it would not stop directly when the user entered 1.
You are also comparing an int with a char ('1'), so in order to exit the loop, the user would have had to enter 49 (the ASCII value for 1), not 1.
You are also mixing formatted input (cin >> x) with unformatted input (getline). I suggest that you stick to one only.

Example:

while(cout << "Enter 1 to stop\n", getline(cin, input) && input != "1") {
    bookQ.push_back(input);
}

Hannon qaoud · Answer 2 · 2022-07-03T20:08:20.130

0

simply check if input is 1 everytime the user enters somthing, and when it does = 1, simply break loop.

string x;
while (true) {                                 // require a loop to input string and  end when user prompts                      
    cout << "Enter 1 to stop" << endl;
    cin >> x;
    if (x == "1"){
       break;
    }
    getline(cin, x);
    bookQ.push_back(x);
}
}

edited Jul 03 '22 at 20:08

answered Jul 03 '22 at 19:55

Hannon qaoud

785
2
21

Still runs indefinitely after first input – Hendrik Jul 03 '22 at 19:59

score 0 · Answer 3 · answered Jul 03 '22 at 20:03

Assuming you meant that input is a string, then you've made a few mistakes with types. First of all, you've used wrong type for variable x, you used int which is integer type, and the type string is required. Secondly, when comparing x with '1' you used single quotes, which define the type of variable as char, not string. To make 1 a string you should use double quotes, like so "1". Besides that, you have used for(condition), which is incorrect syntax. You should use while(condition). Also, when your loop iterates, the x variable is the input book name, and input variable is always an empty string, so I would suggest replace input with x everywhere. The working code is below.

P.S. I am not sure whether you want "1" to be in the final vector, so I haven't changed that

#include <iostream>
#include <vector>
#include <string>

using namespace std;

int main() {
    vector<string> bookQ = {"what", "book", "is", "that", "you", "are", "reading"};
    for (int i = 0; i < bookQ.size(); i++) {
        cout << bookQ[i] << ' ';
    }
    cout << endl;

    string input;
    string x;
    while (x != "1") {
        cout << "Enter 1 to stop" << endl;
        cin >> x;

        bookQ.push_back(x);
    }

    for (int i = 0; i < bookQ.size(); i++) {
        cout << bookQ[i] << ' ';
    }
    cout << endl;

    return 0;
}

This is better than my answer, unfortunately it adds the final `"1"` to the end of the vector. — john, Jul 03 '22 at 20:08

score 0 · Answer 4 · answered Jul 03 '22 at 20:32

First, your for syntax is wrong. You want a while loop instead, or in this case a do..while loop would make more sense. Also, you are pushing the user's input into the vector before validating what the input actually is.

Second, x is an integer, but '1' is a character whose ASCII value is number 49. Your loop will never end, because != will always be true. Since you want the user to enter number 1 to stop the loop, you need to drop the quotes:

Third, what is the point of pre-populating bookQ? Just declare the bookQ without any initial data, and then cout the entire question as a normal string. This way, after the user is done entering input, the vector will contain only the user's input and nothing else.

Try something more like this:

#include <iostream>
#include <vector>
#include <string>
#include <iomanip>
using namespace std; 

int main()
{
    vector <string> bookQ;
    string input;

    cout << "what book is that you are reading" << endl;

    do {
        cout << "Enter a book, or 1 to stop" << endl;
        getline(cin >> ws, input);
        if (input == "1") break;
        bookQ.push_back(input);
    }
    while (true);

    for (size_t i = 0; i < bookQ.size(); ++i) {
        cout << bookQ[i] << ' ';
    }
    cout << endl;

    return 0;
}

C++ Loop for String

4 Answers4