C Program to Convert Hexadecimal to Decimal

Converting numbers from one base to another is pretty handy in programming. Got a hexadecimal number '1A3'? You’ll need its decimal equivalent. In C, it's easy to whip up a program for this conversion. You'll break each character of the hexadecimal number down into its decimal equivalent, then sum 'em up. Let’s see how you can do it.

Prerequisites for the Hexadecimal to Decimal Program in C

Before you start coding, ensure you have these concepts clear:

• Understanding of strlen() for string length
• Usage of loops like while or for
• Basic knowledge of character operations and ASCII values
• Any C compiler such as GCC 9 or newer — or just run it in the EduSeekho online compiler

Source Code of C Program to Convert Hexadecimal to Decimal

Here's the complete C code that converts a hexadecimal number to its decimal equivalent:

#include <stdio.h>
#include <string.h>

int main() {
    char hexInput[20];
    long decValue = 0;
    int length, base = 1, index, decDigit;
    
    printf("Enter a hexadecimal number: ");
    scanf("%s", hexInput);
    
    length = strlen(hexInput);
    
    for (index = length - 1; index >= 0; index--) {
        if (hexInput[index] >= '0' && hexInput[index] <= '9') {
            decDigit = hexInput[index] - '0';
        } else if (hexInput[index] >= 'A' && hexInput[index] <= 'F') {
            decDigit = hexInput[index] - 'A' + 10;
        } else if (hexInput[index] >= 'a' && hexInput[index] <= 'f') {
            decDigit = hexInput[index] - 'a' + 10;
        }
        decValue += decDigit * base;
        base *= 16;
    }
    printf("Decimal value: %ld\n", decValue);
    
    return 0;
}

Output of the Hexadecimal to Decimal Program

When you run the program and input a hexadecimal number, it will display the decimal conversion:

Enter a hexadecimal number: 1A3
Decimal value: 419

Algorithm to Convert Hexadecimal to Decimal in C

Converting a hexadecimal number to a decimal involves understanding and processing each character of the string from right to left. Here is the step-by-step algorithm the program uses:

1. Read the hexadecimal string from the user.
2. Initialize decValue to zero.
3. Find the length of the string.
4. Loop through each character of the string from end to start.
5. Convert each character to its decimal equivalent.
6. Multiply the converted value with the power of 16 based on its position.
7. Add the result to decValue.
8. Continue until all characters are processed.
9. Print the decValue as the decimal equivalent.

flowchart TD
  A([Start]) --> B[/Read hexInput/]
  B --> C[decValue = 0]
  C --> D[length = strlen(hexInput)]
  D --> E[index = 0]
  E --> F{index < length?}
  F -->|Yes| G[character = hexInput[index]]
  G --> H{"character >= '0' && character <= '9'?"}
  H -->|Yes| I[decDigit = character - '0']
  H -->|No| J{"character >= 'A' && character <= 'F'?"}
  J -->|Yes| K[decDigit = character - 'A' + 10]
  J -->|No| L{"character >= 'a' && character <= 'f'?"}
  L -->|Yes| M[decDigit = character - 'a' + 10]
  M --> O
  K --> O
  I --> O
  O[decValue = decValue * 16 + decDigit] --> P[index = index + 1]
  P --> F
  F -->|No| Q[/Print decValue/]
  Q --> R([End])

How the C Program to Convert Hexadecimal to Decimal Works

Let's break down how each part of the program functions.

• #include <stdio.h> and #include <string.h>: These headers include the standard input-output library and string handling functions.
• char hexInput[20]: This array stores the hexadecimal string input by the user. The size can be adjusted based on expected input length.
• long decValue = 0: Initializes the variable that will hold the decimal equivalent of the input string.
• int length, base = 1, index, decDigit: Declare variables to handle the string length, the base for multiplication (initially 1, representing 16^0), the loop index, and the decimal digit equivalent for each character.
• scanf("%s", hexInput): Reads the hexadecimal string from the user.
• length = strlen(hexInput): Calculates the length of the string using the strlen() function.
• for loop: Iterates over each character from the end of the string to the beginning.
• if condition: This checks if the current character is between '0' and '9', 'A' and 'F', or 'a' and 'f', and then converts it into a decimal digit.
• decValue += decDigit * base: Adds the calculated decimal digit value to the total based on the current power of 16.
• base *= 16: Multiplies the base by 16 as the loop progresses, adjusting the weight for the next digit to the left.
• printf("Decimal value: %ld\n", decValue): Outputs the final decimal value of the input hexadecimal string.

Time and Space Complexity of the Hexadecimal to Decimal Conversion

Understanding the efficiency of this program helps when dealing with large inputs.

Time Complexity: O(n). The time grows linearly with the number of characters in the hexadecimal string. Here, n is the number of digits in the hexadecimal number — for example, it is 3 if the input is '1A3'. The for loop processes each character once, so 4 characters mean 4 iterations.

Space Complexity: O(1). The program utilizes a fixed amount of space regardless of the input size, using only the variables hexInput, decValue, length, base, index, and decDigit — making a total of six.

Key takeaway:Hexadecimal conversion needs careful handling of character values and powers of 16.

FAQs About C Program to Convert Hexadecimal to Decimal

Here are common questions students ask when learning about converting hexadecimal numbers to decimal in C.

Related Programs

If you found this program helpful, check out these related programs:

• C Program to Convert Binary to Decimal with Code and Output
• C Program to Convert Binary to Octal with Sample Output
• C Program to Convert Binary to Decimal and Vice-Versa
• C Program to Convert Decimal to Octal
• C Program to Convert Octal to Binary with Example

Conclusion

Converting from hexadecimal to decimal is a cool way to grasp different number bases in programming. Once you're comfy with it, try writing a C program to convert decimal numbers back to hexadecimal. It's a fun way to deepen your understanding of these ideas. Keep at it, and you’ll see how this logic applies in real-world situations.

Challenge yourself to tackle more C programs. Check out our C language quiz and give coding a shot with the EduSeekho online compiler.