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// wrote C# code for this

static int PowerTO16(int power) //helper function
{
int num = 1;
while (power > 0)
{
num *= 16;
power--;
}
return num;
}

static int htoi(string str)
{
int length = str.Length;
int power = 0;
int num = 0;
int sum = 0;

for (int i = length - 1; i >= 0; i--)
{
if (str[i] >= '0' && str[i] <= '9')
{
num = (Convert.ToInt32(str[i] - '0') * PowerTO16(power));
}
else if ((str[i] - 'A') >= 0 && (str[i] - 'F') <= 0)
{
int s = str[i] - 'A';
s += 10;
num = s * PowerTO16(power);
}
else
return Int32.MinValue;

sum += num;
power++;
}
return sum;
}

- KJ May 16, 2009 | Flag Reply

int power (int a, int b) // utility function
{
int res = 1 ;
while( b>0 )
{
res *= a ;
b--;
}
return ( res );
}

int htoi ( char* s )
{
int result = 0;
int value =0;
int len = strlen(s);
int exp = len;
char c;
int i;

for( i=0; i<len; i++)
{

c = s[i];

if ( c >='1' && c<='9')
new_result = (int)( (c - '0') * power(16, exp-1) );

else if (c >='A' && c<='F')
new_result = (int)( (c - 55) * power(16, exp-1) );

exp --;
result += new_result;

}

return (result);
}

- A^2 - Apple Aspirant June 02, 2009 | Flag Reply

Above answer is "the" Correct answer. Using power is inefficient.

- Correct September 09, 2009 | Flag Reply

Here's Python:

# efficient, lazy-evaluation of base powers
def pow(b):
    p = 1
    while 1:
        yield p
        p *= b

# pre-compute hashtable of hex digit conversions
def hexdigit2int_tbl():
    xlat = {}
    for i in range(10):
        xlat[str(i)] = i
    for i in range(6):
        c = chr(ord('a')+i)
        C = chr(ord('A')+i)
        xlat[c] = xlat[C] = i+10
    return xlat

# validate input hex string
# optional 2nd argument only evaluated once at first use
def is_hex(h, xlat=hexdigit2int_tbl()):
    for d in h:
        if d not in xlat:
            return False
    return True

def htoi(h, xlat=hexdigit2int_tbl()):
    if not is_hex(h):
        return None
    return sum(xlat[d]*p for d, p in zip(h[::-1], pow(16)))

print(htoi('g')) # not hex, return None
print(htoi('123456789AbCdEf0'))

- Bullocks December 29, 2009 | Flag Reply

assuming the string is in upper case

int htoi(char *hex)
{
    int result = 0;
    while (*hex) {
        result = result * 16 + *hex - 'A' >= 0 ? *hex = 'A' + 10 : *hex - '0';
        *hex++;
    }
}

- Anonymous October 07, 2010 | Flag Reply

struct Foo{
char *pName;
char *pAddress;
};
main(){
struct Foo *obj = malloc(sizeof(struct Foo));
clrscr();
obj->pName = malloc(100);
obj->pAddress = malloc(100);
strcpy(obj->pName,"Your Name");
strcpy(obj->pAddress, "Your Address");
free(obj);
printf("%s", obj->pName);
printf("%s", obj->pAddress);
}

- Anonymous June 03, 2012 | Flag Reply

long htoi(NSString* hex)
{
    NSString *h = [hex uppercaseString];
    long result = 0;
    for (int i = 0; i < hex.length; i++) {
        unichar c = [h characterAtIndex:i];
        if ((c >= '0' && c <= '9') || (c >= 'A' && c <= 'F')) {
            if(c >='A' && c <='F')
                result=result * 16+ (c -'A'+10);
            else
                result=result * 16+ (c -'0');
            
        }
        else {
            return -1;
        }
    }
    return result;
}

- Anonymous July 10, 2012 | Flag Reply

Java Solution:

public void HexToInt(String s)
	{
		char[] cArr=s.toCharArray();
	
		HashMap<Character, Integer> hexVal=new HashMap<Character,Integer>();
		hexVal.put('A', 10);
		hexVal.put('B', 11);
		hexVal.put('C', 12);
		hexVal.put('D', 13);
		hexVal.put('E', 14);
		hexVal.put('F', 15);
		
		int intVer=0;
		int counter=0;
		for(int i=cArr.length-1; i>=0; i--)
		{
			if(hexVal.containsKey(cArr[i]))
			{
				intVer=intVer+ (int) Math.pow(16, counter)*hexVal.get(cArr[i]);
			}
			else
			{
				intVer=intVer+((int) Math.pow(16, counter))*Character.getNumericValue(cArr[i]);
			}
			counter++;
		}
		
		System.out.println("\nhexToInt:" + intVer);
			
	}

- ATuring September 01, 2014 | Flag Reply

{{{ #include <iostream> using namespace std; int htoi(char* c) { int result = 0; for(int i = 0; c[i] != '\0'; i++) { if(c[i] >= '0' && c[i] <= '9') { result = (result * 16) + c[i] - '0'; } else if(c[i] >= 'A' && c[i] <= 'F') { result = (result * 16) + c[i] - 'A' + 10; } else if(c[i] >= 'a' && c[i] <= 'f') { result = (result * 16) + c[i] - 'a' + 10; } else { cout << "Invalid character" << endl; return -1; } } return result; } int main() { char* c = "24D65"; cout << htoi(c) << endl; return 0; } - akshaycj47 November 09, 2015 | Flag Reply

public class HexaDecimalToInteger {
	
	public static void convertToDecimal(String hexStr){
		int maxPower = hexStr.length()-1;
		int sum=0;
		
		for(int i=0;i<=hexStr.length()-1;i++){
			int digit=0;
			if(hexStr.charAt(i) >= '0' && hexStr.charAt(i) <= '9'){  // between 0 and 9
				digit = hexStr.charAt(i) - '0';
			}else{ // between A and E
				digit = 10 + (hexStr.charAt(i) - 'A');
			}
			sum = sum*16 + digit; // optimized way to convert
		}
		
		System.out.println("Decimal : " + sum);
	}
		
	public static void main(String[] args) {
		String hexStr ="23AE";
		convertToDecimal(hexStr);
	}
}

- Mayank Jain August 23, 2017 | Flag Reply

int htoi(string hex)
{
    int i,retv=0;
    
    for(i=0;i<hex.size();i++)
    {
      if(hex[i]>='A' && hex[i]<='F')
      {
      retv=retv*16+ (hex[i]-'A'+10);
      continue;
      }
      
      else
      retv=retv*16+ (hex[i]-'0' );
      
      }
      
      
      return retv;
      
      }

- Anonymous July 25, 2009 | Flag Reply