C Exercises: Convert a string to a double

Last update on July 29 2025 12:55:10 (UTC/GMT +8 hours)

14. String to Double Conversion (Advanced)

Write a C program to convert a string to a double.

Sample Solution:

C Code:

#include<stdio.h>      // Include the standard input/output header file.
#include<stdlib.h>     // Include the standard library header file.

int main ()          // Start of the main function.
{
double num1, num2;   // Declare two double variables 'num1' and 'num2'.
char my_array[256];   // Declare a character array 'my_array' with a maximum size of 256.

printf ( "\n Input a number : " );   // Prompt the user to input a number.
fgets (my_array, 256, stdin);   // Read a line of input from the user and store it in 'my_array'.

    num1 = atof (my_array);   // Convert the string in 'my_array' to a double and store it in 'num1'.
    num2 = num1/2;   // Calculate half of 'num1' and store it in 'num2'.

printf (" The original number is : %f \n", num1);   // Print the original value of 'num1'.
printf (" After division by 2 the number is : %f\n\n", num2);   // Print the value of 'num2' after division by 2.

return 0;   // Return 0 to indicate successful execution of the program.
}   // End of the main function.

Sample Output:

Input a number : 25                                                                                          
The original number is : 25.000000                                                                           
After division by 2 the number is : 12.500000

Flowchart:

For more Practice: Solve these Related Problems:

Write a C program to convert a string to a double using strtod() and then perform arithmetic operations on the result.
Write a C program to convert a string with a decimal point to a double and display it with fixed precision.
Write a C program to convert a string to a double and compare it with another double for equality within a tolerance.
Write a C program to convert a string to a double and compute its square root while handling conversion errors.

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