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  1. #1
    Join Date
    Jan 2017

    How can I convert the strings to integers?

    Hello, everybody can y'all be so kind to help me with my program? I am trying to convert strings to integers. This is my task:
    Open a file "numbers.txt"
    read integer numbers as strings from the file (one number per line)
    convert each string to a numeric representation (without using stoi() or similar functions from the string library)
    store converted numbers in an array
    close "numbers.txt"

    So far I have read integer numbers as strings but cannot convert the string array to integers without using the string library. Can someone help? My code won't compile but I am trying to do this: 154: Sum = 4*1 + 5*10 + 1*100 = 154 so it can convert to an integer.
    This is what I have so far:
    #include <fstream>
    #include <string>
    #include <sstream>
    #include <iostream>
    using namespace std;
    int StringToInteger( string arraySize);
    int main()
       ifstream infile;"numbers.txt");
       const int size = 1000;
       string myArray[size];
       int i = 0;
       while (infile >> myArray[i])
          cout << "The string is \"" << myArray[i] << "\"" << endl;
          cout << i << endl;
    int StringToInteger( string arraySize)
       int values = 0;
       for (int index = 0; index < arraySize.size; index++) {
          values *= 10;
          values += (arraySize[index] - '0');
       return values;

  2. #2
    2kaud's Avatar
    2kaud is offline Super Moderator Power Poster
    Join Date
    Dec 2012

    Re: How can I convert the strings to integers?

    StringToInteger() requires a type string as a parameter and you are passing i which is of type int.

    for (int index = 0; index < arraySize.size; index++) {
    .size is a function and so should be
    for (int index = 0; index < arraySize.size(); index++) {
    If you are required to store the converted numbers in an array, why are you defining myArray as being of type string? Shouldn't this be of type int? Also why are reading the string from the file into myArray? Why not just read it into a string variable, then convert it and store it into the required array?

    Also you are not checking that the file has been opened OK. Also what happens if there are more lines in the file then the specified size of the array?
    All advice is offered in good faith only. All my code is tested (unless stated explicitly otherwise) with the latest version of Microsoft Visual Studio (using the supported features of the latest standard) and is offered as examples only - not as production quality. I cannot offer advice regarding any other c/c++ compiler/IDE or incompatibilities with VS. You are ultimately responsible for the effects of your programs and the integrity of the machines they run on. Anything I post, code snippets, advice, etc is licensed as Public Domain and can be used without reference or acknowledgement. Also note that I only provide advice and guidance via the forums - and not via private messages!

    C++23 Compiler: Microsoft VS2022 (17.2.2)

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