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#include <stdio.h>
#include <math.h>
#include <string.h>
int dtb(int d);
int dto(int d);
void dth(int d);
int btd(int b);
int otd(int o);
int htd(char p[]);
int main()
{
	int inp,mid,out;
	char a,in[20],ou[20];
	printf("a = BINARY TO DECIMAL\nb = BINARY TO OCTAL\nc = BINARY TO HEXADECIMAL\nd = DECIMAL TO BINARY\ne = DECIMAL TO OCTAL\nf = DECIMAL TO HEXADECIMAL\ng = OCTAL TO BINARY\nh = OCTAL TO DECIMAL\ni = OCTAL TO HEXADECIMAL\nj = HEXADECIMAL TO BINARY\nk = HEXADECIMAL TO OCTAL\nl = HEXADECIMAL TO DECIMAL\n\n\nEneter the function which you want to peform(number): ");
	scanf("%c", &a);
	switch(a)
	{
		case 'a':
			printf("Enter Binary value: ");
			scanf("%d" , &inp);
			out = btd(inp);
			printf("%d is its Decimal equivalent.",out);
			break;
		case 'b':
			printf("Enter Binary value: ");
			scanf("%d" , &inp);
			mid = btd(inp);
			out = dto(mid);
			printf("%d is its Octal equivalent.",out);
			break;	
		case 'c':
			printf("Enter Binary value: ");
			scanf("%d" , &inp);
			mid = btd(inp);
			dth(mid);
			break;
		case 'd':
			printf("Enter Decimal value: ");
			scanf("%d" , &inp);
			out = dtb(inp);
			printf("%d is its binary equivalent.",out);
			break;
		case 'e':
			printf("Enter Decimal value: ");
			scanf("%d" , &inp);
			out = dto(inp);
			printf("%d is its Octal equivalent.",out);
			break;
		case 'f':
			printf("Enter Decimal value: ");
			scanf("%d", &mid);
			dth(mid);
			break;
		case 'g':
			printf("Enter Octal value: ");
			scanf("%d" , &inp);
			mid = otd(inp);
			out = dtb(mid);
			printf("%d is its binary equivalent.",out);
			break;
		case 'h':
			printf("Enter Octal value: ");
			scanf("%d" , &inp);
			out = otd(inp);
			printf("%d is its Decimal equivalent.",out);
			break;
		case 'i':
			printf("Enter Octal value: ");
			scanf("%d" , &inp);
			mid = otd(inp);
			dth(mid);
			break;
		case 'j':
			printf("Enter Hexadecimal value: ");
			scanf("%s" , in);
			mid = htd(in);
			out = dtb(mid);
			printf("%s is its binary equivalent.",dtb(htd(in)));
			break;
		case 'k':
			printf("Enter Hexadecimal value: ");
			scanf("%s" , in);
			mid = htd(in);
			out = dto(mid);
			printf("%d is its Octal equivalent.",out);
			break;
		case 'l':
			printf("Enter Hexadecimal value: ");
			scanf("%s" , in);
			out = htd(in);
			printf("%d is its decimal equivalent.",out);
			break;
		default:
		printf("Error!!!! Please try again.");	
	}	
	return 0;
}
int dtb(int d)
{
	int sum = 0,i = 0;
	while(d != 0 )
	{
		sum += (d%2)*pow(10,i);
		i++;
		d /= 2;
	}
	return sum;
}
int dto(int d)
{
	int sum = 0,i = 0;
	while(d != 0 )
	{
		sum += (d%8)*pow(10,i);
		i++;
		d /= 8;
	}
	return sum;
}
void dth(int d)
{
	char ans[20],hexa[] = {'0','1','2','3','4','5','6','7','8','9','A','B','C','D','E','F','\0'};
	int a,i = 0;
	    while(d != 0)
    {
        ans[i] = hexa[d%16];
        i++;
        d /= 16;
    }
    printf("%s is its Hexadecimal equivalent.",strrev(ans));
}
int btd(int b)
{
	int sum = 0, i = 0;
	while(b != 0)
	{
		sum += (b%10)*pow(2,i);
		i++;
		b /= 10;
	}
	return sum;
}
int otd(int o)
{
	int sum = 0, i = 0;
	while(o != 0)
	{
		sum += (o%10)*pow(8,i);
		i++;
		o /= 10;
	}
	return sum;
}
int htd(char p[])
{
	int sum = 0,i;
	for(i = strlen(p) - 1 ; i >=0 ; i--)
	{
		if(p[i] <= '9' && p[i] >= '0')
		{
			sum += (p[i] - 48)*pow(16,i);
		}
		else if(p[i] <= 'F' && p[i] >= 'A')
		{
			sum += (p[i] - 55)*pow(16,i);
		}
	}
	return sum;
}