C :

#include<stdio.h> 
#include<string.h> 
#include<math.h> 
int main() 
{  
    int tran(char s[]);  
    char s[20];   
    int n;   
    gets(s);   
    n=tran(s);   
    printf("%d\n",n); 
} 
int tran(char s[]) 
{  
    int i,n,re=0;  
    n=strlen(s);  
    for(i=0;i<n;i++)  
    {   
        if(s[n-1-i]>='0' && s[n-1-i]<='9')    
            re=re+(s[n-1-i]-'0')*pow(16,i);   
        if(s[n-1-i]>='a' && s[n-1-i]<='f')    
            re=re+(s[n-1-i]-'a'+10)*pow(16,i);    
        if(s[n-1-i]>='A' && s[n-1-i]<='F')     
            re=re+(s[n-1-i]-'a'+10)*pow(16,i);  
    }   
    return(re);  
} 

C++ :

#include <cstdio>
int main(void) {
    int d, sum=0;
    scanf("%x", &d);
    printf("%d\n", d);
    return 0;
}

Pascal :

program e20150206;
var
 s:string;
 i,len,cm,tmp:integer;
 sum:real;
begin
 readln(s);
 len:= length(s);
 cm:=len-1;
 sum:=0;
 for i:=1 to len do
  begin
   tmp:=ord(s[i]);
   //writeln(tmp);
   case tmp of
    65,97: sum:=sum+10*exp(ln(16)*cm);
    66,98: sum:=sum+11*exp(ln(16)*cm);
    67,99: sum:=sum+12*exp(ln(16)*cm);
    70,100: sum:=sum+13*exp(ln(16)*cm);
    71,101: sum:=sum+14*exp(ln(16)*cm);
    72,102: sum:=sum+15*exp(ln(16)*cm);
    else
     sum:=sum+(tmp-48)*exp(ln(16)*cm);
    end;
    dec(cm);
   end;
  writeln(sum:0:0);
end.