decimal to octal conversion in c programming (using code blocks) - c

Question

Decimal to octal conversion c.using code blocks 16.01.the conversion works until 63.This is my first time posting here
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
// conversion of decimal to octal
int main()
{
int num,sum,count,x,y;
printf("enter a number\t");
scanf("%d",&num);
count = 0;
sum = 0;
while (num>0){
x=num%8;
x=x*pow(10,count);
count=count+1;
num=num/8;
sum=sum+x;
}
printf("\n%d",sum);
return 0;
}

Answer 1

#include <stdio.h>
#include <stdlib.h>
// conversion of decimal to octal
int main()
{
int num,i,len=0,x[100];
printf("enter a number\t");
scanf("%d",&num);
while (num>0){
x[len]=num%8;
num=num/8;
len++;
}
for(i=len;i>=0;i--)
printf("\n%d",x[i]);
return 0;
}
This will work for the conversion from decimal to octal.
Note: Check the logic works!.Make the sum long int. After 63 your int no longer able to hold the answer.

Answer 2

The problem with the code is actually reported by the compiler if you turn on some warnings, however the problem is that you are implicitly converting from double to int, and depending on the implementation, you'd lose precision. pow returns a double but you're storing it in an int (x)
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
// conversion of decimal to octal
int main()
{
int num,sum,count,x,y;
printf("enter a number\t");
scanf("%d",&num);
count = 0;
sum = 0;
while (num>0){
x=num%8;
x=x*pow(10,count);
/* ^^^^^^^^^^^^^^^^ problem here */
count=count+1;
num=num/8;
sum=sum+x;
}
printf("\n%d",sum);
return 0;
}
now the fix
Instead of using the library pow, you should implement your own that's integer only (because you KNOW you are using ints only)
/* a trivial implementation */
long pow10(int n) {
long result = 1;
while(n--) {
result *= 10;
}
return result;
}
Now to clean up the program a bit:
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
long pow10(int n);
/* a trivial implementation */
long pow10(int n) {
long result = 1;
while(n--) {
result *= 10;
}
return result;
}
int main()
{
int num, count;
long sum, x;
printf("enter a number\t");
scanf("%d",&num);
count = 0;
sum = 0;
while (num>0){
x=num%8;
x=x*pow10(count);
count=count+1;
num=num/8;
sum=sum+x;
}
printf("\n%ld",sum);
return 0;
}