How to perform forced type conversion in C language

In C language, you can perform forced type conversion through the "(type_name) expression" statement. The parameter "type_name" represents the name of the new type. For example, "(float)100" converts the value 100 of the int type. It is of float type. Forced type conversion is a type conversion that is explicitly proposed by the programmer and needs to be specified through code in a specific format. When programming, it is a good programming habit to use the forced type conversion operator whenever type conversion is needed. .

The operating environment of this tutorial: windows7 system, c99 version, Dell G3 computer.

Data type conversion is to convert data (variables, values, expression results, etc.) from one type to another.

C language has two data type methods:

• Automatic type conversion: It is the data type conversion performed silently, implicitly, and secretly by the compiler. This This conversion does not require programmer intervention and occurs automatically.

• Forced type conversion

Let’s take a closer look at the forced type conversion in C language.

Forced type conversion

Automatic type conversion is the result of the compiler's own judgment based on the context of the code. Sometimes it is not so "intelligent" ” cannot meet all needs. If necessary, programmers can also explicitly propose type conversion in the code themselves, which is called forced type conversion.

Automatic type conversion is a type conversion performed silently and implicitly by the compiler and does not need to be reflected in the code; forced type conversion is explicitly proposed by the programmer and needs to be performed through code in a specific format. Specifies a type conversion. In other words, automatic type conversion does not require programmer intervention, while forced type conversion requires programmer intervention.

The format of forced type conversion is:

(type_name) expression

• ##type_name is the new type name

• expression is an expression

For example:

(float) a;  //将变量 a 转换为 float 类型
(int)(x+y);  //把表达式 x+y 的结果转换为 int 整型
(float) 100;  //将数值 100（默认为int类型）转换为 float 类型

Please see the following example, using the cast operator to divide an integer variable by another Integer variable, get a floating point number:

#include <stdio.h>
 
int main()
{
   int sum = 17, count = 5;
   double mean;
 
   mean = (double) sum / count;
   printf("Value of mean : %f\n", mean );
 
}

It should be noted here that the priority of the cast operator is greater than division, so the value of sum is first converted to double type , and then divided by count to obtain a value of type double.

Type conversion can be implicit, performed automatically by the compiler, or explicit, specified by using the cast operator. When programming, it is a good programming habit to use the cast operator whenever type conversion is needed.

Type conversion is only temporary

Whether it is automatic type conversion or forced type conversion, it is only temporary for this operation. Sexual conversion, the conversion result will also be saved to the temporary memory space, and the original type or value of the data will not be changed. Please look at the following example:

#include <stdio.h>
int main(){
    double total = 400.8;  //总价
    int count = 5;  //数目
    double unit;  //单价
    int total_int = (int)total;
    unit = total / count;
    printf("total=%lf, total_int=%d, unit=%lf\n", total, total_int, unit);
    return 0;
}

Pay attention to the 6th line of code. The total variable is converted to int type before being assigned to the total_int variable. This conversion does not affect The type and value of the total variable itself. If the value of total changes, then the output result of total will become 400.000000; if the type of total changes, then the output result of unit will become 80.000000.

Extended knowledge: Commonly used arithmetic conversions

Commonly used arithmetic conversions implicitly force values ​​to the same type. The compiler first performs integer promotion, and if the operand types are different, they are converted to the highest level type occurring in the following hierarchy:

Usual arithmetic conversions do not apply For assignment operators, logical operators && and ||. Let us see the following example to understand this concept:

#include <stdio.h>
 
int main()
{
   int  i = 17;
   char c = &#39;c&#39;; /* ascii 值是 99 */
   float sum;
 
   sum = i + c;
   printf("Value of sum : %f\n", sum );
 
}

When the above code is compiled and executed, it produces the following results:

Value of sum : 116.000000

Here, c is first converted to integers, but since the final value is of type float, the usual arithmetic conversions are applied, and the compiler converts i and c to floating point types and adds them to get a floating point number.

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