c++手动将string转换为int

C++ manually Convert string to int?

本文关键字：转换 int string c++      更新时间：2023-10-16

我试图手动将字符串转换为int，并且我遇到了困难。我首先检查输入的字符串是否是整数。接下来，我想在不使用任何标准库方法的情况下将该字符串转换为整数。

当我在循环中逐行运行代码时，它做了我需要它做的事情，但是当我在循环中运行它时，它吐出了错误的二进制结果。

==>我将检查您输入的值是否为数字。

==>输入号码:234

==>输入结果:1

==>按enter键继续…

= => 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;
}

将for循环改为:

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

并使newNumber为double

希望有帮助!!

我修改你的代码:

    // 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;
}

希望能有所帮助。

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