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#1
September 30th, 2012, 07:15 PM
 lisa92
Contributing User

Join Date: Oct 2011
Posts: 43
Time spent in forums: 10 h 33 m 29 sec
Reputation Power: 3
Hex to decimal conversion

The conversion doesn't work when I use lower case letters. I'm not sure if I have to do -7 or something else.

Code:
```
// Program accepts an 8 digit hexadecimal input and outputs
// the corresponding value in decimal

#include <stdio.h>

main()
{

int decimal = 0; //integer for the final decimal number
int bit; //integer representing numbers between 0-9 and letter a-f in hex number
char hexnumber[100]; //a char array containing the input hex number

int i=0,j=0;

scanf("%s",&hexnumber);

//the integer i takes the length of the input array
i =strlen(hexnumber);

//while there is a next bit in the array
while(i!=0)
{
bit = hexnumber[j];

//if the bit is a digit do the following
if(('0' <= bit && bit <= '9'))
{
decimal = decimal * 16;
decimal = decimal + (bit - '0');
}

//if the bit is a letter do the following
if(('a' <= bit && bit <= 'z'))
{
decimal = decimal * 16;
decimal = decimal + (bit - '7');
}

i--;
j++;

}

printf("The decimal representation of this number is : %d\n",decimal);

}```

#2
September 30th, 2012, 09:41 PM
 Lux Perpetua
Contributing User

Join Date: Feb 2004
Location: San Francisco Bay
Posts: 1,939
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Code:
```    //if the bit is a letter do the following
if(('a' <= bit && bit <= 'z'))
{
decimal = decimal * 16;
decimal = decimal + (bit - '7');
}```
Only the letters a through f are valid hexadecimal digits. More importantly, what in the heck is bit - '7'?

#3
September 30th, 2012, 11:56 PM
 WaltP
Registered User

Join Date: Feb 2004
Posts: 20
Time spent in forums: 2 h 29 m 18 sec
Reputation Power: 0
What is the binary value of '0'?
What is the binary value of 'A'?
What is the binary value of 'a'?

If '0' must become 0, what do you have to subtract?
If 'A' must become 10, what do you have to subtract?
If 'a' must become 10, what do you have to subtract?

#4
October 1st, 2012, 10:18 AM
 b49P23TIvg
Contributing User

Join Date: Aug 2011
Posts: 4,173
Time spent in forums: 1 Month 3 Weeks 2 Days 11 h 21 m 42 sec
Reputation Power: 455
uh, why don't you just use scanf("%x",&space_for_an_integer);
or is the 8 digit hex number permitted to be a fraction?
__________________
[code]Code tags[/code] are essential for python code!

#5
October 2nd, 2012, 05:42 AM
 WaltP
Registered User

Join Date: Feb 2004
Posts: 20
Time spent in forums: 2 h 29 m 18 sec
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Quote:
 Originally Posted by b49P23TIvg uh, why don't you just use scanf("%x",&space_for_an_integer); or is the 8 digit hex number permitted to be a fraction?

In what way does using this suggestion teach how to convert values from one base to another? What if the next assignment is to convert to binary. Or base 6, base 20, base 36?

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