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What is type conversion in C language?

Type conversion refers to the ability to convert data from one data type to another in C programming. C allows both implicit and explicit type conversions.

C programming allows manipulating variables and values of different data types. Variables are declared with a specific data type that determines the size, range, and operations that can be performed on them. However, it is sometimes required to convert the type of a variable or value to another compatible data type in order to complete an operation or assignment. For example, an int variable may need to be converted to float for certain calculations. C provides mechanisms to convert between its basic data types like int, float, double, char etc.

Implicit Type Conversion

Implicit type conversion, also known as automatic type conversion, refers to the automatic conversion of values from one data type to another compatible type done by the compiler. Implicit conversions are performed when:

  • Assigning a value of a basic data type to a variable of another compatible basic data type. For example assigning an int value to a float variable.
  • Using values of different basic data types in an expression. For example using an int and a float value in an expression.
  • Passing arguments to a function that expects parameters of different basic data types.

In implicit conversion, the compiler automatically converts the value to the destination data type without any additional syntax required from the programmer. Some examples:

int x = 10; 
float y;
y = x; // int x converted to float implicitly

int a = 15;
float b = 12.5;
float sum = a + b; // a and b implicitly converted to float 

Here are some important points about implicit type conversions in C:

  • They automatically widen the type conversion hierarchy without data loss. For example int is converted to float.
  • No syntax is required, conversion is done automatically by compiler.
  • Conversions from lower to higher ranking types are allowed. For example, float to double.
  • Conversions from higher to lower ranking types can result in loss of data and precision.

Explicit Type Conversion

Explicit conversions, also known as casts, are a way to forcibly convert a value from one data type to another specified type. Unlike implicit conversion, explicit casting requires additional syntax provided by the programmer.

Explicit type conversions in C are done using the typecast operator -(type) preceding the value to be converted. For example:

float f = 3.1415;
int i;
i = (int)f; // f value converted explicitly to int

Here are some key points about explicit type conversions:

  • Allows conversion between any two compatible data types, even non-widening conversions.
  • Provides a way to explicitly handle data narrowing, precision loss, overflow etc.
  • Useful when implicit conversion does not give desired result.
  • Overrides default type promotion in expressions.
  • Required syntax is typecasting using (type) value notation.

Explicit conversions are useful in cases like:

  • Converting a float value to int by truncating the fractional part.
  • Converting a higher data type like double to a lower type like float with possible precision loss.
  • Converting a non-numeric type like char to numeric type like int.

Type Conversion Rules and Hierarchy

C defines a logical hierarchy and ranking of its basic data types. This hierarchy determines compatibility and precedence for implicit type conversions. The general ranking from highest to lowest is:

  1. double
  2. float
  3. unsigned long int
  4. long int
  5. unsigned int
  6. int
  7. short int
  8. unsigned char
  9. signed char
  10. _Bool

Some key type conversion rules based on this hierarchy are:

  • Lower ranking type is implicitly converted to higher ranking type in assignments and expressions.
  • Higher ranking types are truncated when converted to lower ranking types.
  • Signed integers are automatically converted to unsigned integers when mixed, but not vice versa.
  • Explicit casting can convert between any two compatible types in either direction.

Understanding this basic type hierarchy and conversion rules is important to utilize conversions effectively and avoid unintended results.

Type Conversion Errors

Invalid type conversions can lead to compilation errors or unintended results during program execution. Some common problems faced during conversions are:

  • Loss of precision – Converting higher precision type like double to lower type like float can lose precision.
  • Loss of magnitude – Converting larger type to smaller type can lead to overflow and loss of magnitude.
  • Truncation – Converting floating point to integer discards fractional part resulting in truncation.
  • Incompatible pointers – Pointers to different types are incompatible for conversion.
  • Violation of const qualifier – Conversion cannot discard const qualifier of a type.
  • Compiler errors – Attempting invalid implicit conversions results in compilation errors.

To avoid such problems, care should be taken to use proper type conversions by:

  • Using explicit casts instead of relying on implicit conversions.
  • Converting to the correct destination type size and signedness.
  • Using helper functions like floor(), ceil() etc for floating point conversions.
  • Checking results of conversions to ensure correct values as required.

Type Conversion Use Cases

Some typical use cases where type conversion is used in C programs are:

  • Mathematical operations – Converting operands to common compatible type.
  • Function calls – Cast arguments to expected parameter types.
  • Input/output – Convert string or character input to numeric types.
  • Type safety – Explicitly convert values to safer types like unsigned ints.
  • Storage – Convert values to types that require less storage.
  • Standard libraries – Libraries use specific types for arguments and return values.
  • Portability – Define portable sized types like int32_t for conversions.

Proper use of type conversions allows programmers to write code that works across platforms with varied data types and representation sizes.


Type conversion is an essential concept in C that allows conversion of values between its different data types. Implicit conversion is done automatically by the compiler, while explicit casting requires programmer specified syntax but provides finer control. Understanding the type hierarchy, conversion rules and potential pitfalls is important to leverage conversions effectively. Used properly, type conversions enhance code portability, safety and precision across numeric data types in C.