C program to convert Binary to Decimal number system

Example

Input

Input number: 0011

Output

Decimal: 3

Logic to convert binary to decimal number system

/**
 * C program to convert binary number system to decimal number system
 */

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

#define BASE 2

int main()
{
    long long binary, decimal=0, tempBinary;
    int N=0;

    printf("Enter any binary number: ");
    scanf("%lld", &binary);

    tempBinary = binary;

    while(tempBinary!=0)
    {
        /* If current binary digit is 1 */
        if(tempBinary % 10 == 1)
        {
            decimal += pow(BASE, N);
        }

        N++;
        tempBinary /= 10;
    }

    printf("Binary number = %lld\n", binary);
    printf("Decimal number= %lld", decimal);

    return 0;
}

/*
Output :

Enter any 16 bit binary value: 0100000010001100
Binary value = 0100000010001100
Decimal value = 16524
*/

Another approach using two’s complement

/**
 * C program to convert binary to decimal number system
 */

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

#define SIZE 16 /* N-bit binary number */

void getTwosComplement(char *twosComp, const char *);

int main()
{
    char binary[SIZE + 1], tempBinary[SIZE + 1];
    int i, j, signBit = 0;
    long long decimal = 0;

    printf("Enter any %d bit binary value: ", SIZE);
    gets(binary);

    strcpy(tempBinary, binary);

    /*
     * If sign bit is on find two's complement of the binary number
     */
    if(binary[0] == '1')
    {
        signBit = 1;
        getTwosComplement(tempBinary, binary);
    }

    /*
     * Convert decimal to binary number
     */
    for(i=0; i<SIZE; i++)
    {
        if(tempBinary[i] == '1')
        {
            decimal += pow(2, (SIZE - (i+1)));
        }
    }

    if(signBit==1)
    {
        decimal *= -1;
    }

    printf("Binary value = %s\n", binary);
    printf("Decimal value = %lld", decimal);

    return 0;
}

/*
 * Gets the 2's complement of the binary value.
 */
void getTwosComplement(char * twosComp, const char * binary)
{
    char onesComp[SIZE + 1];
    int i, carry=1;

    /*
     * Finds 1's complement of the binary number
     */
    for(i=0; i<SIZE; i++)
    {
        if(binary[i]=='1')
        {
            onesComp[i] = '0';
        }
        else if(binary[i]=='0')
        {
            onesComp[i] = '1';
        }
    }
    onesComp[SIZE] = '\0';

    /*
     * Adds 1 to 1's complement of the binary number to get 2's complement
     */
    for(i=SIZE-1; i>=0; i--)
    {
        if(onesComp[i]=='1' && carry==1)
        {
            twosComp[i] = '0';
        }
        else if(onesComp[i]=='0' && carry==1)
        {
            twosComp[i] = '1';
            carry = 0;
        }
        else
        {
            twosComp[i] = onesComp[i];
        }
    }
    twosComp[SIZE] = '\0';
}

/*
Output :

Enter any 16 bit binary value: 0100000010001100
Binary value = 0100000010001100
Decimal value = 16524
*/