The formula of Binary to Decimal is:

Decimal Number = (n

^{th}digit of binary number) * 2^{(n-1)}+ ((n-1)^{th}digit of binary number) * 2^{(n-2)}+ …… + (1^{st}digit of binary number) * 2^{(0)}
Suppose 1101 is the binary number. Then the decimal number will be:

Decimal Number = (1 * 2

^{3}+ 1 * 2^{2}+ 0 * 2^{1}+ 1* 2^{0}) = (8 + 4 + 0 + 1) = 13
Here is the C program to convert Binary Number into Decimal Number:

#include <stdio.h> #include <math.h> int main() { int binary, decimal = 0, i, j=0; printf("Enter a binary number: "); scanf("%d",&binary); int temp; temp = binary; if(temp>0){ i = temp % 10; if(i==0 || i==1){ while(temp!=0){ i = temp % 10; decimal = decimal + i * pow(2, j); temp = temp / 10; j++; } } } if(decimal==0 || binary<0) printf("The number is not a binary number !"); else printf("The equivalent decimal number of %d is : %d.",binary,decimal); return 0; }

**NB:**Here pow(x,y) is a function that comes with header file math.h. It returns x to the power y.

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