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C Program to Convert Binary to Decimal

In this article, we will learn how to create a program in C that converts any given binary number (provided by the user at run-time) to its equivalent decimal value. At last, we have also created a program for the same purpose using a user-defined function named BinToDec().

But before going through the program, if you are not aware of how the binary to decimal conversion takes place, then refer to the step-by-step process of binary to decimal conversion. Now let's move on to the program.

Binary to Decimal in C

To convert a binary number to a decimal number in C programming, you have to ask the user to enter the binary number and then convert it into a decimal number, as shown in the following program:

#include<stdio.h>
#include<conio.h>
#include<math.h>
int main()
{
    int binnum, decnum=0, i=0, rem;
    printf("Enter any binary number: ");
    scanf("%d", &binnum);
    while(binnum!=0)
    {
        rem = binnum%10;
        decnum = decnum + rem*pow(2,i);
        i++;
        binnum = binnum/10;
    }
    printf("\nEquivalent Decimal Value = %d", decnum);
    getch();
    return 0;
}

Because the above program was written in the Code::Blocks IDE, you will receive the following output after a successful build and run. This is the first snapshot of the sample run:

c program convert number from binary to decimal

Now supply any binary number, say 101110, and press the ENTER key to see its equivalent value in the decimal number system, as shown in the second snapshot of the sample run given below:

binary to decimal conversion in c

Program Explained

Binary to Decimal in C without pow() Function

Now let's create the same program, but this time without using any pow() function of math.h library. The question is, Write a program in C that converts any given binary number to decimal number without using any pow() function. The answer to this question is:

#include<stdio.h>
#include<conio.h>
int main()
{
    int binnum, decnum=0, i=1, rem;
    printf("Enter any binary number: ");
    scanf("%d", &binnum);
    while(binnum!=0)
    {
        rem = binnum%10;
        decnum = decnum + (rem*i);
        i = i*2;
        binnum = binnum/10;
    }
    printf("\nEquivalent Decimal Value = %d", decnum);
    getch();
    return 0;
}

Here is the final snapshot of the sample run of the above program:

c binary to decimal without pow function

Here we have replaced pow(2, i) (0 as the initial value of i) with i (1 as the initial value of i) and i++ with i=i*2. Therefore, in this case, we will get:

We obtain the same results as in the case of pow(2, i), namely:

Binary to Decimal in C using a User-Defined Function

Now let's create another program in C that uses a user-defined function named BinToDec() to convert any given binary number into its equivalent decimal value, as shown in the program given below:

#include<stdio.h>
#include<conio.h>
int BinToDec(int bin);
int main()
{
    int binnum, decnum;
    printf("Enter any binary number: ");
    scanf("%d", &binnum);
    decnum = BinToDec(binnum);
    printf("\nEquivalent Decimal Value = %d", decnum);
    getch();
    return 0;
}
int BinToDec(int bin)
{
    int dec=0, i=1, rem;
    while(bin!=0)
    {
        rem = bin%10;
        dec = dec + (rem*i);
        i = i*2;
        bin = bin/10;
    }
    return dec;
}

Here is the final snapshot of the sample run:

c binary to decimal using function

Here we have used a function named BinToDec() that takes one argument as a binary number. Inside the function, we have converted the given binary number to a decimal number. The decimal number is stored inside a variable dec. And we have returned the value of dec to the function. Therefore, inside the main() function, we have initialized the returning value of function BinToDec() to a variable decnum that holds the value of dec in the BinToDec() function. Finally, print the value of decnum as output, which will be the equivalent decimal value of the given binary number.

The same program in different languages

C Quiz

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