Common data type conversion problems and solutions in C++

Common data type conversion problems and solutions in C

Introduction:
In C programming, conversions between different data types are often encountered question. Correct data type conversion is one of the keys to ensuring program correctness and performance. This article will introduce some common data type conversion problems and provide corresponding solutions and specific code examples.

1. Implicit type conversion
In C, there are many situations where the compiler will automatically perform type conversion. This conversion is called implicit type conversion. Implicit type conversion may cause data precision loss or operation errors. For example:

int a = 10;
double b = 3.14;

double c = a / b; // 预期结果为3.3333，但实际结果为3

In the above code, a and b are variables of int and double types respectively. The result of a / b is automatically converted to int type, causing the decimal part of the result to be truncated.

Solution:

1. Explicit conversion:
   In order to avoid errors caused by automatic conversion, you can use static_cast to explicitly convert the data type. Modify the above code as follows:

int a = 10;
double b = 3.14;

double c = static_cast<double>(a) / b; // 结果为3.3333

By using static_cast, we explicitly tell the compiler that a needs to be converted to double type.

2. Optimize the calculation order:
   The above code can also avoid type conversion problems by optimizing the calculation order:

int a = 10;
double b = 3.14;

double c = a / (double)b; // 结果为3.3333

By converting b to double type, the calculation result will be the expected value.

2. String and numeric type conversion
In C, conversion between string and numeric types is common and important. Below are some common string and numeric type conversion problems and corresponding solutions.

1. Convert string to numeric type:

   #include <iostream>
   #include <string>
   
   int main() {
    std::string str = "12345";
   
    int num = std::stoi(str); // string to int
    long long_num = std::stol(str); // string to long
    float float_num = std::stof(str); // string to float
    double double_num = std::stod(str); // string to double
   
    std::cout << num << std::endl; // 输出：12345
    std::cout << long_num << std::endl; // 输出：12345
    std::cout << float_num << std::endl; // 输出：12345.0
    std::cout << double_num << std::endl; // 输出：12345.0
   
    return 0;
   }

2. Convert numeric type to string:

   #include <iostream>
   #include <string>
   
   int main() {
    int num = 12345;
    long long long_num = 123456789;
    float float_num = 3.14159;
    double double_num = 2.71828;
   
    std::string str_num = std::to_string(num); // int to string
    std::string str_long_num = std::to_string(long_num); // long to string
    std::string str_float_num = std::to_string(float_num); // float to string
    std::string str_double_num = std::to_string(double_num); // double to string
   
    std::cout << str_num << std::endl; // 输出：12345
    std::cout << str_long_num << std::endl; // 输出：123456789
    std::cout << str_float_num << std::endl; // 输出：3.14159
    std::cout << str_double_num << std::endl; // 输出：2.71828
   
    return 0;
   }

   Summary:
   This article introduces common data type conversion problems in C and corresponding solutions. For implicit type conversions, we can use explicit conversions or optimize the order of calculation to avoid problems. For the conversion of string and numeric types, we can use stoi, stol, stof, stod to convert strings to numeric types, and use to_string to convert numeric types to strings. Correct data type conversion helps improve program correctness and performance. In the actual programming process, we should pay attention to potential problems with type conversion and choose appropriate methods for conversion.

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