Detecting if input string has a space

Question

I wrote this code to detect if an input string has a space or not. Please tell what is wrong in this approach.

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

int main(){
    string inp;
    getline(cin, inp);


    for (int i = 0; i < inp.length(); i++) {
        string z = to_string(inp[i]);
        if (z == " ") {
            cout << "space";
        }
        else {
            i++;
        }
    }
}

If i enter a string with spaces, it doesn't print "space".

There is no need for incrementing "i" in the else clause. What are your results without it? It may be skipping the spaces altogether. — Heladio Amaya
– Heladio Amaya, Commented Jun 11, 2019 at 18:06
Answer given already, you might still want to consider std::find(inp.begin(), inp.end(), ' ') – and if you don't want to, you might consider a range based for loop: for(auto c : inp) { if(c == ' ') .... — Aconcagua
– Aconcagua, Commented Jun 11, 2019 at 18:15
@Aconcagua std::string has its own find() method: inp.find(' ') — Remy Lebeau
– Remy Lebeau, Commented Jun 11, 2019 at 22:34

TrebledJ · Accepted Answer · 2019-06-11 18:14:22Z

6

Since inp is an std::string, inp[i] will be a char. Since std::to_string only has overloads for arithmetic, non-char values, calling it on a char is akin to calling it on the integer representation of said char. (If you log z, you'll likely find a number printed.)

Instead, directly compare inp[i] to a space. else { i++; } is also unnecessary – you may be jumping over spaces.

for (int i = 0; i < inp.length(); i++) {
    if (inp[i] == ' ') {    // note single quotes for char
        cout << "space";
    }
}

edited Jun 11, 2019 at 18:14

answered Jun 11, 2019 at 18:07

TrebledJ

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Comments

Remy Lebeau · Accepted Answer · 2019-06-11 22:39:00Z

@TrebledJ's answer explains why your code is broken and how to fix it.

Another way to handle this situation is to use std::string::find() instead:

#include <iostream>
#include <string>

int main(){
    std::string inp;
    std::getline(std::cin, inp);

    if (inp.find(' ') != std::string::npos) {
        std::cout << "space";
    }
}

Alternatively, your original code tries to output "space" for each space character found. You could use find() in a loop:

#include <iostream>
#include <string>

int main(){
    std::string inp;
    std::getline(std::cin, inp);

    std::string::size_type idx = inp.find(' ');
    while (idx != std::string::npos) {
        std::cout << "space at " << idx << std::endl;
        idx = inp.find(' ', idx+1);
    }
}

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