Question

I am trying to compare a string and a char like below :

char filter = "    " // <<== this is a tab space, so I am assuming its one char
if ( line[counter] == filter[0]){

}

note that line is a normal string defined like : string line;. now for some reason the statement is never true even though there are no syntax errors.

UPDATE

inside line is :
string line = "1 90 74 84 48 76 76 80 85";

2nd UPDATE

here is the complete function I wrote :

void getResults(string line){

    int tmpSize = line.length();
    int counter = 0;
    int tmpCounter = 0;

    while(counter != MAX_No_Of_Grades){

        if(line[counter] == '\t\t'){
            counter++;
        }else{
            cout << tmpCounter << ". this is : " << line[tmpCounter] << "a" << endl;
            tempGrade[counter] += line[tmpCounter];
        }
        tmpCounter++;
    }


}

the function is technically suppose to break the string line into an array by “tabspace”. but right now counter does not change and therefore its an endless loop!

Answer 1

I’m not sure what code you are actually running, because the char filter = " " line has no terminator and that assignment is definitely illegal. You cannot assign the string literal (a char array) to a single char variable.

If you want to determine whether the nth character of a string is a tabulation, the following code would probably be what you are looking for:

if (line[counter] == '\t') {
  // match...
}

---

As for updates. If typed as string line = "1 90 74 84 48 76 76 80 85"; in your program, there are no tabulations in this string. There are only spaces. Moreover, '\t\t' is a pair of tables. Put a single \t in there for a single tab.

Here is a slightly modified version of your sample function:

void getResults(string line)
{
    int tmpSize = line.length();
    int counter = 0;
    int tmpCounter = 0;
    while((tmpCounter < tmpSize) && (counter != MAX_No_Of_Grades))
    {
        if(line[counter] == ' ') {
            counter++;
        }
        else {
            cout << tmpCounter << ". this is : " << line[tmpCounter] << "a" << endl;
            tempGrade[counter] += line[tmpCounter];
        }
        tmpCounter++;
    }
}

This version has an extra check in the while loop to stop consuming characters after the end of line is reached. It also uses a space character since your test input does not use tabulations.

---

If this is not homework and you can use all the standard library facilities you want, I would suggest looking into more advanced input strategies. Here is a simplified version of your function to extract every single number in the array.

#include <iostream>
#include <string>
#include <sstream>
void getResults ( const std::string& line )
{
    std::istringstream input(line);
    for (int grade=0; input >> grade;) {
        // process grade.
    }
}

If you want to remove the global variable and handle any number of grades, you can use a std::vector<> to automatically increase the “array” size as you get more and more grades.

#include <iostream>
#include <string>
#include <sstream>
#include <vector>
std::vector<int> getResults ( const std::string& line )
{
    std::istringstream input(line);
    std::vector<int> grades;
    for (int grade=0; input >> grade;) {
        grades.push_back(grade);
    }
    return grades;
}