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Convert a Char Array into a Double in C

Introduction to Char Array in C

In C programming, a char array is a sequence of characters stored in consecutive memory locations. It is also known as a string, which is a common data type used to represent text data.

A char array is declared using the char data type followed by square brackets that indicate the number of characters the array can hold.

Here, array_name is the name of the char array, and size is the number of characters that the array can hold. For example, the following code declares a char array named "str" that can hold up to 20 characters:

You can initialize a char array using a string literal like this:

In this case, the size of the array is automatically determined by the length of the string literal, including the null character at the end.

You can also assign individual characters to the array like this:

This assigns the characters 'h', 'e', 'l', and 'p' to the char array named "my_string".

You can access individual elements of a char array using array indexing notation like this:

You can also use pointer notation to manipulate char arrays since the name of a char array can be treated as a pointer to its first element. For example:

Note that in C, a string is always terminated with a null character ('\0') which is automatically added at the end of a string literal. This is important to remember when working with char arrays, as it can affect the behavior of functions that operate on strings.

Introduction to double in C

In C programming language, double is a data type used to represent floating-point numbers with double precision. It is used to store decimal numbers that require more precision than what can be provided by a float data type. Double data type occupies 8 bytes (64 bits) in memory, which is twice the size of a float data type.

The Double data type provides a higher degree of accuracy and can store numbers with greater range and precision than the float data type. It is commonly used in scientific and engineering applications where high precision is required.

In C, the double data type is declared using the keyword double. For example, the following code declares two double variables:

The Double data type supports the same arithmetic operations as other numeric data types in C, such as addition, subtraction, multiplication, and division. However, due to the higher precision of double, the result of arithmetic operations can be more accurate and less prone to rounding errors than with other data types.

The Double data type is a powerful tool for working with floating-point numbers in C programming language, providing higher precision and range than other data types.

strtod() function: How it converts a char array into a double:

In C programming language, the strtod() function is used to convert a string to a double data type. It takes two arguments: a pointer to a character string to convert and a pointer to a character string that points to the first character after the converted value in the original string.

If the conversion fails, the strtod() function returns the converted double value or zero. If the entire string cannot be converted to a double value, strtod() returns the largest double value that can be represented and sets the errno variable to ERANGE.

Here's the syntax of the strtod() function:

An example that demonstrates how to use the strtod() function to convert a string to a double:

In this example, we have a string "3.14" that we want to convert to a double value. We pass the string and a pointer to a character pointer variable endptr1 to the strtod() function. The endptr1 variable stores the first character's address that could not be converted to a double. The string had no non-convertible characters, so the endptr1 is an empty string.

After the conversion, we print the double and endptr values to the console.

The output of the program will be:

Value1: 3.140000
Value2: 3.140000
End Pointer 1: 
End Pointer 2: ab5

Steps to convert a char array into a double:

A step-by-step guide on how to do it:

Step 1 - Include the necessary header files - Before using the strtod() function, you must include the stdlib.h header file that contains the function definition.

Step 2 - Declare the char array - Declare a char array representing the string to convert to a double.

Step 3 - Declare a pointer to a char array - Declare a pointer to a char array that will be used to point to the first non-converted character after the double value.

Step 4 - Call the strtod() function - Call the strtod() function and pass the char array and the pointer to the char pointer variable.

Step 5 - Check for conversion errors - Check if the endptr points to the null character at the end of the char array. If it doesn't, then the conversion failed, and you should handle the error appropriately.

Step 6 - Use the double value - Use the converted double value in your program.

A simple C Program to Convert a Char Array into a Double:


Double value: 3.141590


In this example, the char_array variable contains a string representation of the value 3.14159. The strtod() function is used to convert this string to a double value, which is stored in the double_value variable. The second argument to strtod() is set to endptr.

After the conversion is complete, the double_value variable contains the converted value, which is printed to the console using printf().

Improvements to the above program

The program can be strengthened in the following ways to make converting a char array to a double more reliable:

  1. While taking input, use fgets() instead of scanf() - When reading numerous inputs or inputs of different types, scanf() may leave unread characters in the input buffer, which might cause problems. To read input and avoid these problems, use fgets() instead.
  2. Validate user input - You can verify that the input only contains characters that are appropriate for a double value before converting the input to a double (digits, decimal point, sign, and exponent). This can aid in avoiding errors brought on by improper input.
  3. Handle overflow and underflow - The program will return an infinite or zero value if the input is either too big or too tiny to fit in a double. Before converting the input to a double, you can check for overflow and underflow and respond appropriately.
  4. Allow for different base values - The base ten value is what strtod() assumes by default. Use the strtol() or strtoll() routines if you work with input in a different base.


In conclusion, the strtod function, which is a component of the standard C library, can be used to convert a char array into a double in C. This function accepts a string as input and outputs a double value that matches the string's numeric value.

When using the strtod function, looking for potential errors that could arise from improper input string formatting is critical. The endptr argument supplied to the strtod's value can be used to check for certain problem scenarios.

Overall, using strtod to convert a char array to a double in C is a simple operation that might be helpful when processing numerical information from users or external sources.

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