C Program to Convert Between Hexadecimal, Octal, Binary and Decimal Numbers

This program deals with four number systems. They are:

• Decimal (base 10)
• Binary (base 2)
• Octal (base 8)
• Hexadecimal (base 16)

Here i post a  program for following operations:

• Decimal to binary conversion
• Decimal to Octal conversion
• Decimal to Hexadecimal conversion
• Binary to Decimal conversion
• Binary to Octal conversion
• Binary to Hexadecimal conversion
• Octal to Decimal conversion
• Octal to Binary conversion
• Octal to Hexadecimal conversion
• Hexadecimal to Decimal conversion
• Hexadecimal to Binary conversion
• Hexadecimal to Octal conversion

The following program lets you convert between the four number systems; decimal, binary, octal and hexadecimal number systems.

#include<stdio.h>
#include<string.h>

char* reversestring(char *a)
{
int i,l;
char *r;
l=strlen(a);
r=(char*)malloc(l*sizeof(char));
for(i=0;i<l;i++)
  r[i]=*(a+l-i-1);
r[i]='\0';
return r;
}

char*DecToHex(int dec)
{
char hex[10];
int i=0,tnum,rem;
tnum=dec;
while(tnum!=0)
{
rem=tnum%16;
hex[i++]=rem<=9?'0'+rem:'A'+rem-10;
tnum/=16;
}
hex[i]='\0';
return(reversestring(hex));
}

int DecToOct(int dec)
{
int oct=0;
int i=1,tnum,rem;
tnum=dec;
while(tnum!=0)
{
rem=tnum%8;
oct=i*rem+oct;
tnum/=8;
i=i*10;
}
return(oct);
}

int DecToBin(int dec)
{
int bin=0;
int i=1,tnum,rem;
tnum=dec;
while(tnum!=0)
{
rem=tnum%2;
bin=i*rem+bin;
tnum/=2;
i*=10;
}
return(bin);
}

int BinToDec(int bin)
{
int rem,dec=0,base=1;
int num;
num=bin;
while(num>0)
   {
  rem = num % 10;
  dec = dec + rem * base;
  num = num / 10 ;
  base = base * 2;
  }
return dec;
}

int HexToDec(char* hex)
{
int dec=0,base=1,i,d;
char c;
i=strlen(hex)-1;
while(i>=0)
{
c=*(hex+i);
if(c>='A'&&c<='F')
  d=10+c-'A';
else if(c>='a'&&c<='f')
  d=10+c-'a';
else
  d=c-'0';
dec+=d*base;
base*=16;
i--;
}
return dec;
}

int OctToDec(int oct)
{
int dec=0,base=1;
int t;
t=oct;
while(t>0)
{
dec+=(t%10)*base;
t/=10;
base*=8;
}
return dec;
}

void main()
{
int inputnum,from,to,fromto,out;
char inputs[10];
char *outs;
printf("\nChoose the number system to convert from.\n");
printf("From:\n1.Decimal\n2.Binary\n3.Octal\n4.Hexadecimal\n");
scanf("%d", &from);
printf("\nenter the number.\n");
if(from<4)
  scanf("%d",&inputnum);
else
  scanf("%s",inputs);
printf("Choose the number system to convert to.\n");
printf("To:\n1.Decimal\n2.Binary\n3.Octal\n4.Hexadecimal\n");
scanf("%d", &to);
fromto=from*10+to;
switch(fromto)
  {
  case 12:out=DecToBin(inputnum);break;
  case 13:out=DecToOct(inputnum);break;
  case 14:outs=DecToHex(inputnum);break;
  case 21:out=BinToDec(inputnum);break;
  case 23:out=DecToOct(BinToDec(inputnum));break;
  case 24:outs=DecToHex(BinToDec(inputnum));break;
  case 31:out=OctToDec(inputnum);break;
  case 32:out=DecToBin(OctToDec(inputnum));break;
  case 34:outs=DecToHex(OctToDec(inputnum));break;
  case 41:out=HexToDec(inputs);break;
  case 42:out=DecToBin(HexToDec(inputs));break;
  case 43:out=DecToOct(HexToDec(inputs));break;
  }
if(to==4)
  printf("\n%s",outs);
else
  printf("\n%d",out);
  }