01  #include<stdio.h>
02  
03  long bin2dec(char binaryString[]);
04  
05  int main()
06  {
07   char bstr[20];
08   long decNum;
09  
10   printf("Enter binary string (0-1) : ");
11   gets(bstr);
12  
13   decNum=bin2dec(bstr);
14  
15   if(decNum==-1)
16   {
17    printf("Invalid string.");
18   }
19   else
20   {
21    printf("Decimal number : %ld",decNum);
22   }
23  
24   return 0;
25  }
26  
27  long bin2dec(char binaryString[])
28  {
29  long dnum=0;
30   int i=0;
31   int n;
32  
33   while(binaryString[i]!='')
34   {
35    n=binaryString[i]-48; /* convert char '0' or '1' into integer 0 or 1 */
36  
37   /*check for 0 and 1 */
38  
39   if(n!=0 && n!=1)
40    return -1; // invalid string
41  
42    dnum=(dnum*2)+n;
43    i++;
44   }
45  
46  return(dnum);
47  
48   }

 
 OUTPUT :
 
 Enter binary string (0-1) : 110011
 Decimal number : 51