Decimal to Binary conversion using C Programming

Decimal to binary conversion is a fundamental concept in computer programming. In C, we can convert decimal numbers to their binary representation using simple mathematical operations and functions.

Syntax

long decimalToBinary(int decimal_number);

Method 1: Using Function with Mathematical Approach

This method uses modulo and division operations to extract binary digits and build the binary number −

#include <stdio.h>

long decimalToBinary(int dno) {
    long bno = 0, rem, f = 1;
    while (dno != 0) {
        rem = dno % 2;
        bno = bno + rem * f;
        f = f * 10;
        dno = dno / 2;
    }
    return bno;
}

int main() {
    int dno;
    long bno;
    printf("Enter any decimal number: ");
    scanf("%d", &dno);
    bno = decimalToBinary(dno);
    printf("The Binary value is: %ld<br>", bno);
    return 0;
}

Enter any decimal number: 12
The Binary value is: 1100

Method 2: Using Array to Store Binary Digits

This approach stores binary digits in an array and prints them in reverse order −

#include <stdio.h>

void decimalToBinaryArray(int dno) {
    int binary[32];
    int i = 0;
    
    if (dno == 0) {
        printf("Binary: 0<br>");
        return;
    }
    
    while (dno > 0) {
        binary[i] = dno % 2;
        dno = dno / 2;
        i++;
    }
    
    printf("Binary: ");
    for (int j = i - 1; j >= 0; j--) {
        printf("%d", binary[j]);
    }
    printf("<br>");
}

int main() {
    int dno;
    printf("Enter a decimal number: ");
    scanf("%d", &dno);
    decimalToBinaryArray(dno);
    return 0;
}

Enter a decimal number: 25
Binary: 11001

Binary to Decimal Conversion

Here's the reverse conversion from binary to decimal using the power function −

#include <stdio.h>
#include <math.h>

int binaryToDecimal(long bno) {
    int dno = 0, i = 0, rem;
    while (bno != 0) {
        rem = bno % 10;
        bno /= 10;
        dno += rem * pow(2, i);
        ++i;
    }
    return dno;
}

int main() {
    long bno;
    int dno;
    printf("Enter a binary number: ");
    scanf("%ld", &bno);
    dno = binaryToDecimal(bno);
    printf("The decimal value is: %d<br>", dno);
    return 0;
}

Enter a binary number: 10011
The decimal value is: 19

How It Works

• Decimal to Binary: Divide the number by 2 repeatedly and collect remainders in reverse order.
• Binary to Decimal: Multiply each binary digit by powers of 2 and sum them up.
• The mathematical approach builds the binary number as a long integer.
• The array method is more flexible for larger binary numbers.

Conclusion

Decimal to binary conversion in C can be implemented using mathematical operations or arrays. Both methods effectively demonstrate the relationship between decimal and binary number systems in programming.