String_int

[NielsNIO]

Hello,

I have the following situation:

I want to check if the char in a string is the same as an int.

So lets say:

int one = 1;
string test = "1234";

for(n = 0; n<4; n++)
{
if (string[n] == one) // this always comes back negative

{
action
}

}
Do I need to convert it to an int, and if so how do I do that?

Thanks,

Niels

[kempofighter]

The character '1' does not have the value of 1 so there is no way to do a direct comparison.
http://www.codeguru.com/forum/showth...760#cpp_string

You can have instant gratification by reading the FAQs. They will provide the tools that you need to do this particular task and there are a few different ways of doing it.

[NielsNIO]

I always used this function to convert from string to int, however if i want to convert a specific value of the string (say: string[n]), this does not work.

string test = "123";
int one = atoi(test.c_str());

cout << one << endl; // returns the integer 123


string test = "123";
int one = atoi(test[1].c_str()); // returns an compilation error C2228: left of '.c_str' must have class/struct/union

cout << one << endl;

[Paul McKenzie]

I always used this function to convert from string to int, however if i want to convert a specific value of the string (say: string[n]), this does not work.

That is because atoi() requires a null-terminated string, not a single char.

string[n] is a single char, not a null-terminated array of char, which is what atoi() requires.

If you're using ASCII, all you need to do is subtract '0'.

#include <string>
#include <iostream>

int main()
{
    std::string test = "123";
    int number = test[0] - '0';
    std::cout << number;
}

If you want a solution using atoi:

#include <string>
#include <iostream>
#include <cstdlib>

int main()
{
    std::string test = "123";
    char ch[2] = {0};  // temporary, 1-character null-terminated buffer
    ch[0] = test[0];
    int number = atoi(ch);
    std::cout << number;
}

#include <string>
#include <iostream>
#include <cstdlib>

int main()
{
    std::string test = "123";
    int number = atoi((test.substr(0,1)).c_str());
    std::cout << number;
}

Regards,

Paul McKenzie

[NielsNIO]

Thank you very much Paul!