if 条件句的练习

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ift条件练习
{
class Program
{
static void Main(string[] args)
{
Console.Write("请输入一个字母:");
int int_a = Console.Read();

if (int_a <= 90 && int_a >= 65)
{
int int_b = int_a + 32;
Console.WriteLine((char)int_b);

}
if (int_a <= 122 && int_a >= 97)
{
int int_b = int_a - 32;
Console.WriteLine((char)int_b);

}
if (int_a <= 97 && int_a >= 90)
{
Console.WriteLine("输入的不是字母，程序结束");
}
if (int_a <= 65)
{
Console.WriteLine("输入的不是字母，程序结束");
}
Console.ReadKey();
}
}
}