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

But before going through the program, if you are not aware of

- Binary Number
- Decimal Number
- Binary to Decimal Conversion

then refer to Binary to Decimal conversion step by step process. Now let's move on to the program.

To convert binary number to decimal number in C programming, you have to ask from user to enter the binary number and then convert it into 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; }

As the above program was written under **Code::Blocks** IDE, therefore after successful build and run, you will get the following
output. This is the first snapshot of the sample run:

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

- Receive any binary number from user at run-time say
**101110** - Create a while loop that runs until the value of
**binnum**(entered binary number from user say**101110**) becomes 0 - In other words, the loop continues running until the value of
**binnum**does not becomes equal to 0. And when the value of**binnum**gets equal to 0, then the program flow goes out from the loop or exits from the**while**loop - At first run of the
**while**loop, the condition**binnum!=0**or**101110!=0**evaluates to be true, therefore program flow goes inside the loop, and**binnum%10**or**101110%10**or**0**gets initialized to**rem** - And
**decnum + rem*pow(2, i)**(we have initialized**decnum**and**i**both with 0 at start of the program. And the function**pow()**of**math.h**library takes two arguments, first argument corresponds to base and second argument corresponds to exponent. That is, in**2**, 2 is base and 3 is exponent) or^{3}**0 + 0*pow(2, 0)**or**0 + 0*2**or^{0}**0 + 0*1**or**0+0**or**0**gets initialized to**decnum** - The value of
**i**gets incremented and becomes 1 - And then
**binnum/10**or**101110/10**or**10111**gets initialized to**binnum** - Now program flow goes back to the condition of the
**while**loop. That is**binnum!=0**or**10111!=0**evaluates to be true, therefore program flow again goes inside the loop - Inside the loop,
**binnum%10**or**10111%10**or**1**gets initialized to**rem** - And then
**decnum + rem*pow(2, i)**or**0 + 1*pow(2, 1)**or**0 + 1*2**or^{1}**2**gets initialized to**decnum** - The value of
**i**gets incremented and becomes 2 - And
**binnum/10**or**10111/10**or**1011**gets initialized to**binnum** - Now the program flow goes back to the condition of the
**while**loop again. There**binnum!=0**or**1011!=0**evaluates to be true, therefore program flow again goes inside the loop - Therefore again
**binnum%10**or**1011%10**or**1**gets initialized to**rem** - And then
**decnum + rem*pow(2, i)**or**2 + 1*pow(2, 2)**or**2 + 1*2**or^{2}**2 + 1*4**or**6**gets initialized to**decnum** - The value of
**i**gets incremented and becomes 3. And then**binnum/10**or**1011/10**or**101**gets initialized to**binnum** - In this way, program flow again goes back to the condition of the
**while**loop and if the condition evaluates to be true, then follow the similar steps as told above to calculate the new value of**rem, decnum, i**, and**binnum**. - That is, at fourth run of the
**while**loop,**rem, decnum, i, binnum**holds its value as**1, 14, 4, 10**respectively - Then at fifth run,
**rem, decnum, i, binnum**holds**0, 14, 5, 1**respectively - And at sixth run,
**rem, decnum, i, binnum**holds**1, 46, 6, 0**respectively - As the value of
**binnum**becomes equal to 0, therefore program flow does not goes inside the loop. And we have**46**as the value of**decnum**which is the equivalent decimal value of given binary number say**101110** - Now print the value of
**decnum**at last of the program

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 above program:

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

- At first run, i equals 1
- At second run, i equals i*2 or 1*2 or 2
- At third run, i equals i*2 or 2*2 or 4
- At fourth run, i equals i*2 or 4*2 or 8
- At fifth run, i equals i*2 or 8*2 or 16
- At seventh run, i equals i*2 or 16*2 or 32

Here we are getting the same values in case of **pow(2, i)**, that are:

- At first run,
**pow(2, 0)**or**2**or^{0}**1** - At first run,
**pow(2, 1)**or**2**or^{1}**2** - At first run,
**pow(2, 2)**or**2**or^{2}**4** - At first run,
**pow(2, 3)**or**2**or^{3}**8** - and so on

Now let's create another program in C that using 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:

Here we have used a function named **BinToDec()** that takes one argument as binary number. Inside the function we have
converted the given binary number to decimal number. The decimal number holds 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** of **BinToDec()** function. Finally print the
value of **decnum** as output that will be the equivalent decimal value of given binary number.

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