Conversion from Binary,octal,Hexa decimal to Binary format

A number is generally represented in decimal system which we use in our daily life.

But a number can be represented using octal,binary and hexadecimal too.

here’s a link which has good information and you can easily understand what are these

number systems(decimal,octal,binary and hexadecimal)

http://www.rapidtables.com/math/number/Numeral_system.htm

Below is the code

#include<stdio.h>
#include<string.h>
#include<math.h>
#include<ctype.h>
main()
{
   int i,j,size=0,x,k=1,value=0,temp,choice,length, sum=0;;
   long int num;
   char name[10],q,test[10],hex[10];
   printf("MENU\n1.From binary to decimal\n2.From octal to decimal\n3.From hexa decimal to decimal\n");
   scanf("%d",&choice);
   switch(choice)
   {
       case 1:
             printf("enter BINARY number\n");
             scanf("%d",&num);
             temp=num;
             size=0;
             while(temp>0)
             {
               temp/=10;
               size++;
             }
             temp=num;
             for(i=0;i<size;i++)
             {
               k=1;
               x=num%10;
               k=pow(2,i);
               value+=k*x;
               num/=10;
             }
             num=temp;
             printf("the number in decimal form is:%d",value);
             break;
        case 2:
             printf("enter OCTAL number\n");
             scanf("%d",&num);
             temp=num;
             size=0;
             while(temp>0)
             {
               temp/=10;
               size++;
             }
             temp=num;
             for(i=0;i<size;i++)
             {
               k=1;
               x=num%10;
               k=pow(8,i);
               value+=k*x;
               num/=10;
             }
             num=temp;
             printf("the number in decimal form is:%d",value);
             break;
           case 3:
               printf("enter hexa decimal number:");
                   scanf("%s",name);
                   strcpy(hex,name);
             for(length=0; hex[length]!='\0'; ++length);
              for(i=0; hex[i]!='\0'; ++i, --length)
              {
       if(hex[i]>='0' && hex[i]<='9')
           sum+=(hex[i]-'0')*pow(16,length-1);
       if(hex[i]>='A' && hex[i]<='F')
           sum+=(hex[i]-55)*pow(16,length-1);
       if(hex[i]>='a' && hex[i]<='f')
           sum+=(hex[i]-87)*pow(16,length-1);
          }
          printf("\n%d",sum);
   
   }
}