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C Program to Convert a Binary Number to a Decimal Number

Last updated on September 24, 2020

The following is a C program to convert a binary number to a decimal number.

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/*******************************************************
 * Program to convert a binary number to decimal number
********************************************************/

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

int main()
{
    long int bin, remainder, decimal = 0, i = 0;       

    printf("Enter a binary number: ");
    scanf("%d", &bin);

    while(bin != 0)
    {
        remainder = bin % 10;
        decimal += remainder * (int)pow(2, i++);
        bin = bin / 10;        
    }

    printf("Decimal: %d", decimal);    

    return 0;
}

Try it now

Expected Output: 1st run:

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Enter a binary number: 100
Decimal: 4

2nd run:

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Enter a binary number: 1000011
Decimal: 67

How it works #

Here are the steps to convert a binary number to a decimal number:

Example 1: Convert binary number 100 to its decimal equivalent.

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=> ( 1 * 2^2 ) + ( 0 * 2^1 ) + ( 0 * 2^0 )
=> 4 + 0 + 0
=> 4

Example 2: Convert binary number 1001 to its decimal equivalent.

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=> ( 1 * 2^3 ) + ( 0 * 2^2 ) + ( 0 * 2^1 ) + ( 1 * 2^0 )
=> 8 + 0 + 0 + 1
=> 9

The following table shows what happens at each iteration of the loop (assuming bin = 10101):