I think you are talking about the number system conversion programs...If you want to convert a decimal number into binary number system then here is the code.. Code: #include<stdio.h> #include<conio.h> #include<math.h> void dec_bin(long int num) // Function Definition { long int rem[50],i=0,length=0; while(num>0) { rem[i]=num%2; num=num/2; i++; length++; } printf("\nBinary number : "); for(i=length-1;i>=0;i--) printf("%ld",rem[i]); } //================================================ void main() { long int num; clrscr(); printf("Enter the decimal number : "); scanf("%ld",&num); dec_bin(num); // Calling function getch(); }