十进制转化八进制，写得不好，望指点？？？？

/*
  * 把数字转化为ascii码
  */
  int getChar_Ascii(int a){
  	switch (a) {
		case 1:
			a +=48;
			break;
		case 2:
			a +=48;
			break;
		case 3:
			a +=48;
			break;
		case 4:
			a +=48;
			break;
		case 5:
			a +=48;
			break;
		case 6:
			a +=48;
			break;
		case 7:
			a +=48;
			break;
		case 8:
			a +=48;
			break;
		case 9:
			a +=48;
			break;
		default:
			a += 48;
			break;
	}
	return a;
  }
/*
 * 十进制转化为八进制
 */
string decimalToOctal(int num){
	vector<int> v;
	int digit = num;
	double i =log(digit)/log(8);
	int pluto = i;
	int t = 0;
	for(int i = pluto;i >= 0;i--){
		double d = pow(8,i);
		int j = 1;
		for(;j <= 7;j++){
			int comPare = d*j;
			if(comPare > digit){
				break;
			}
		}
		v.push_back(j-1);
		t += (d*(j-1));
		digit = num - t;
	}
	char *ch = new char;
	for(int i = 0;i < v.size();i++){
		v[i] = getChar_Ascii(v[i]);
		ch[i] = v[i];
	}
	string str = "0";
	str += ch;
	delete ch;
	return str;
}

望大家指点一二。。。。。。。。。。