C Type Casting

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C Error Handling

C Type Casting

Type casting is converting a variable from one type to another data type. For example, if you want to store a long value into a simple integer, you need to cast the long type to an int type. You can use the cast operator to explicitly convert a value from one type to another, as shown below:

(type_name) expression

Look at the following example, which uses the cast operator to divide one integer variable by another integer variable, resulting in a floating-point number:

Example

#include<stdio.h>
int main()
{
   int sum = 17, count = 5;
   double mean;

   mean = (double)sum / count;
   printf("Value of mean : %fn", mean );
}

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

Value of mean : 3.400000

Here it should be noted that the cast operator has a higher precedence than division, so the value of sum is first converted to double, and then divided by count, yielding a value of type double.

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

Integer Promotion

Integer promotion is the process of converting integer types smaller than int or unsigned int to int or unsigned int. Look at the following example, which adds a character to an integer:

Example

#include<stdio.h>

int main()
{
   int  i = 17;
   char c = 'c'; /* ascii value is 99 */
   int sum;

   sum = i + c;
   printf("Value of sum : %dn", sum);
}

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

Value of sum : 116

Here, the value of sum is 116 because the compiler performs integer promotion, converting the value of 'c' to its corresponding ASCII value before performing the actual addition operation.

Usual Arithmetic Conversion

The usual arithmetic conversion implicitly converts values to a common type. The compiler first performs integer promotion; if the operands have different types, they are converted to the highest type in the following hierarchy:

The usual arithmetic conversion does not apply to the assignment operators, logical operators && and ||. Let us look at the following example to understand this concept:

Example

#include<stdio.h>
int main()
{
   int  i = 17;
   char c = 'c'; /* ascii value is 99 */
   float sum;

   sum = i + c;
   printf("Value of sum : %fn", sum );
}

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

Value of sum : 116.000000

Here, c is first converted to an integer, but since the final value is of type float, the usual arithmetic conversion applies, and the compiler converts i and c to floating-point, then adds them to produce a floating-point number.

C Header Files

C Error Handling

3 Notes   Write a Note

1. #0 sweet bamboo shoots

   102***1933@qq.com 162   If the operands on both sides of an operator are of different types, they must first be converted to the same type. The lower type is converted to a higher type before the operation. The conversion rules are shown in the figure below.

   sweet bamboo shootssweet bamboo shoots

   102***1933@qq.com 9 years ago (2017-09-08)

2. #0 xxxxripxxxx

   roc***lyman@163.com 305   In C, printf can use the %f placeholder for both double and float output, and they can be used interchangeably. Additionally, double can also use %lf.

   However, for scanf input, double must use %lf, and float must use %f; they cannot be mixed.

   xxxxripxxxxxxxxripxxxx

   roc***lyman@163.com 7 years ago (2020-01-10)

3. #0 ssl

   157***1786@qq.com 53   To improve efficiency, C language will directly convert two different types to the higher type for calculation.

   For example, for variables a and b defined and assigned values of type double and int respectively:

   Assuming an a + b operation is performed, then b will be directly implicitly converted to double type before the operation. It should not be understood as a layer-by-layer conversion (i.e., not that b is first converted to unsigned int, then to long => unsigned long => long long => unsigned long long => float => double, and finally the operation is performed).

   p.s: Speaking of operations, for char and short types, they will be implicitly converted to int during operations. Look at the code:

   #include <stdio.h>
   
   int main() {
       char c = 22, ch = 33;
       short m = 23, n = 32;
       printf("%dn", sizeof(c + ch)); //char and char type operation
       printf("%dn", sizeof(m + n)); //short and short type operation
       printf("%d", sizeof(m + ch)); //short and char type operation
       return 0;
   }

   Output:

   4
   4
   4

   This wasn't covered here, so let me supplement the conversion rules:

   1. Assigning float, double, long double to integer types: truncates the decimal part

   As in:

   #include <stdio.h>
   
   int main() {
       float a = 3.8;
       int b = a; //Performs an implicit type conversion
       printf("a=%.2f; b=%d", a, b);
       return 0;
   }

   Based on the conversion rules and implicit type conversion rules, the output is:

   a=3.80; b=3

   2. Assigning integer types to floating-point types (float, double, long double): pads with the required number of decimal places

   Modifying the above code:

   #include <stdio.h>
   
   int main() {
       int a = 8;
       float b = a; //Performs an implicit type conversion
       printf("a=%d; b=%f", a, b);
       return 0;
   }

   Output:

   a=8; b=8.000000 //%f defaults to outputting 6 decimal places

   3. Assigning a shorter type to a longer type: pads the required bits, with other bits padded with 0

   Assume the following definitions:

   char c = 56;
   short num = 67;
   int m;
   long long int n;

   If the following operations are performed:

   m = ((int)c);
   n = ((long long)nu