1. Conversion any base to any base via decimal .

code : 

#include<bits/stdc++.h> using namespace std; int i,j,n,m,e,s,num=0; string st="",str="",ans=""; int base,decimal,toBase,power=1; //Any base --> Decimal int val(char c){     if (c >= '0' && c <= '9') return (int)c - '0';     else  return (int)c - 'A' + 10; } int FromAnyBase(){     for(i=n-1;i>=0;i--)     {         num += val(st[i])*power;         power = base*power;     }     return num; } //Decimal --> Any base char reVal(int num){     if (num >= 0 && num <= 9) return (char)(num + '0');     else  return (char)(num - 10 + 'A'); } string ToAnybase(){       while(decimal>0)     {         char ch = reVal(decimal%toBase);         str = ch +str;         decimal /= toBase;     }     return str; } int main(){     cin>>st>>base>>toBase;     n = st.size();     decimal = FromAnyBase();     cout<<"In decimal : "<<decimal<<endl;     ans = ToAnybase();     cout<<"In base "<<toBase<<" : "<<ans<<endl; }