# C Program to Convert Binary to Decimal Number Using User Defined Function

Question: write a program in C language to read a binary number from a user and convert it to decimal number using a user defined function.

## C Source Code: Binary to Decimal Conversion User Defined Function

```
#include<stdio.h>
/* Function Prototype */
long int binaryToDecimal(long int num);
/* Main Function */
int main()
{
long int binary, decimal;
printf("Enter valid binary number: ");
scanf("%ld", &binary);
decimal = binaryToDecimal(binary);
printf("Binary (%ld) = Decimal (%ld)", binary, decimal);
return(0);
}
/* Function Definition */
long int binaryToDecimal(long int num)
{
long int decimal=0, base=1, rem;
while(num!=0)
{
rem = num%10;
decimal = decimal + base*rem;
base = base * 2;
num = num/10;
}
return decimal;
}
```

Output of above program :

Enter valid binary number: 1011010111 Binary (1011010111) = Decimal (727) Note: ↲ indicates enter is pressed.