uva : 355 - The Bases Are Loaded

#include <iostream>
#include <string>
#include<cstring>
using namespace std;

typedef long long lint;

lint pow(int b, int n){
lint num = 1;
for (int i = 0; i < n; ++i)
num = num * b;
return num;
}

lint convertBase10(char *str, int base){
int len = strlen(str) - 1;
int i, n;
lint number = 0;
for (i = 0; str[i]; ++i){
switch(str[i]){
case 'a':
case 'A': n = 10; break;
case 'b':
case 'B': n = 11; break;
case 'c':
case 'C': n = 12; break;
case 'd':
case 'D': n = 13; break;
case 'e':
case 'E': n = 14; break;
case 'f':
case 'F': n = 15; break;
default: n = str[i]-48;
}
number = number + (n * pow(base, len));
--len;
}
return number;
}

void revStr(char *str){
char temp[100];
int len = strlen(str) - 1;
int i;
for (i = 0; str[i]; ++i){
temp[i] = str[len-i];
}
temp[i] = '\0';
strcpy(str, temp);
}

char* convertBaseOther(lint number, int base){
if (number == 0)
return "0";
char str[100], c;
int i, j;
lint temp;
i = -1;
while (number != 0){
temp = number % base;
number = number / base;

switch(temp){
case 10: c = 'A'; break;
case 11: c = 'B'; break;
case 12: c = 'C'; break;
case 13: c = 'D'; break;
case 14: c = 'E'; break;
case 15: c = 'F'; break;
default: c = temp + 48;
}
str[++i] = c;
}
str[++i] = '\0';
revStr(str);
return str;
}

int chkValid(char *str, int b){
int n, i;
for (i = 0; str[i]; ++i){
switch(str[i]){
case 'a':
case 'A': n = 10; break;
case 'b':
case 'B': n = 11; break;
case 'c':
case 'C': n = 12; break;
case 'd':
case 'D': n = 13; break;
case 'e':
case 'E': n = 14; break;
case 'f':
case 'F': n = 15; break;
default: n = str[i]-48;
}
if (n >= b) return 0;
}
return 1;
}

int main(){
int bFrom, bTo ;
lint number;
char input[100], output[100];
int n;

while (cin >> bFrom >> bTo >> input){
n = chkValid(input, bFrom);
if (n == 0){
cout << input << " is an illegal base " << bFrom << " number" << endl;
continue;
}
number = convertBase10(input, bFrom);
strcpy(output, convertBaseOther(number, bTo));
cout << input << " base " << bFrom << " = " << output << " base " << bTo << endl;
}
}