C++ manually Convert string to int?

问题:

I was trying to manually convert a string to an int, and I have had difficulties. I first check to see if the string entered is an integer. Next, I want to convert that string to an integer without using any library methods.

When I ran the code inside my loop line by line, it did what I needed it to, but when I ran it inside a loop, it spat out incorrect binary results.

==> I am going to check if the value you enter is a number.

==> Enter a number: 234

==> Input result: 1

==> Press enter to continue...

==> 11001

// Darian Nwankwo, Random Programs, August 2, 2015  #include <iostream> #include <string> #include <cmath>  int main(int argc, const char * argv[]) {     std::string number = "";     bool isNumber = false;      std::cout << "I am going to check if the value you enter is a number." << std::endl;     std::cout << "Enter a number: ";     std::cin >> number;     std::cin.ignore();      // Iterate through variable number to check if it is a number     for ( int i = 0 ; i < number.length() ; i++ ) {         if ( number[i] < 48 || number[i] > 57) {             break;         } else {             isNumber = true;         }     }      std::cout << "Input result: " << isNumber << std::endl;      int newNumber = 0;                  // Iterates over the number string variable and converts value to an integer     if (isNumber) {         for ( int i = 0 ; i < number.length() ; i++ ) {             // newNumber += std::pow( 10.0, number.length() )             newNumber = std::pow(10.0, ( number.length() - ( i + 1 ) ) * ( number[i] - '0' ));         }     } else {         std::cout << "Can't convert." << std::endl;     }      char cont;     std::cout << "Press enter to continue..." << std::endl;     std::cin.get(cont);     std::cout << newNumber;      return 0; } 

回答1:

Change your for loop to:

    for ( int i = number.length() -1 ; i >= 0 ; i-- ) {         int power = number.length() - i -1;         newNumber += (std::pow( 10.0,  power) * (number[i] - '0')); 

and make newNumber to double.

Hope it helps !!

回答2:

I modified your code:

    // Darian Nwankwo, Random Programs, August 2, 2015  #include <iostream> #include <string> #include <cmath>  int main(int argc, const char * argv[]) {     std::string number = "";     bool isNumber = true;     // <-----should be default true      std::cout << "I am going to check if the value you enter is a number." << std::endl;     std::cout << "Enter a number: ";     std::cin >> number;     std::cin.ignore();     // Iterate through variable number to check if it is a number     for ( int i = 0 ; i < number.length() ; i++ ) {         if ( number[i] < 48 || number[i] > 57) {             isNumber = false;       // <--- if not number, turn isNumber to be false             break;         }     }      std::cout << "Input result: " << isNumber << std::endl;      int newNumber = 0;                  // Iterates over the number string variable and converts value to an integer     if (isNumber) {         for ( int i = 0 ; i < number.length() ; i++ ) {             // newNumber += std::pow( 10.0, number.length() )             newNumber = newNumber + std::pow(10.0, ( number.length() - ( i + 1 ) )) * ( number[i] - '0' );   // <--- pow() should not include (number[i] - '0') and newNumber should be cumulative         }     } else {         std::cout << "Can't convert." << std::endl;     }      char cont;     std::cout << "Press enter to continue..." << std::endl;     std::cin.get(cont);     std::cout << newNumber;      return 0; } 

Hope it can help.

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