c#实现简单四则运算
Compute("1+2*3/4")
static decimal Compute(string expression)
{
int i = 0;
var r = _Compute(expression, ref i);
if (i != expression.Length) throw new ArgumentException("╮(︶︿︶)╭");
return r;
}
static decimal _Compute(string expression, ref int i)
{
int j;
char c;
decimal? r = null;
decimal t;
int f = 1, f3;
bool f2;
g1:
while (i < expression.Length)
{
c = expression[i];
if (c >= '0' && c <= '9')
{
for (j = i + 1; j < expression.Length; j++)
{
c = expression[j];
if ((c < '0' || c > '9') && c != '.') break;
}
t = decimal.Parse(expression.Substring(i, j - i));
i = j;
goto g2;
}
else if (c == '+' || c == '-')
{
f3 = c == '+' ? 1 : -1;
i++;
while (i < expression.Length)
{
c = expression[i];
if ((c >= '0' && c <= '9') || c == '.')
{
for (j = i + 1; j < expression.Length; j++)
{
c = expression[j];
if ((c < '0' || c > '9') && c != '.') break;
}
t = f3 * decimal.Parse(expression.Substring(i, j - i));
i = j;
goto g2;
}
else if (c == '(')
{
i++;
if (i >= expression.Length) goto exception;
t = _Compute(expression, ref i) * f3;
if (i >= expression.Length) goto exception;
i++;
goto g2;
}
else if (char.IsWhiteSpace(c))
{
i++;
continue;
}
else goto exception;
}
goto exception;
}
else if (c == '(')
{
i++;
if (i >= expression.Length) goto exception;
t = _Compute(expression, ref i);
if (i >= expression.Length) goto exception;
i++;
goto g2;
}
else if (char.IsWhiteSpace(c))
{
i++;
continue;
}
else goto exception;
}
exception:
throw new ArgumentException("╮(︶︿︶)╭");
g2:
while (i < expression.Length)
{
c = expression[i];
if (c == '+' || c == '-')
{
r = r.HasValue ? (r.Value + f * t) : (f * t);
f = c == '+' ? 1 : -1;
i++;
goto g1;
}
else if (c == '*' || c == '/')
{
f2 = c == '*';
i++;
while (i < expression.Length)
{
c = expression[i];
if (c >= '0' && c <= '9')
{
for (j = i + 1; j < expression.Length; j++)
{
c = expression[j];
if ((c < '0' || c > '9') && c != '.') break;
}
if (f2) t *= decimal.Parse(expression.Substring(i, j - i));
else t /= decimal.Parse(expression.Substring(i, j - i));
i = j;
goto g2;
}
else if (c == '+' || c == '-')
{
f3 = c == '+' ? 1 : -1;
i++;
while (i < expression.Length)
{
c = expression[i];
if ((c >= '0' && c <= '9') || c == '.')
{
for (j = i + 1; j < expression.Length; j++)
{
c = expression[j];
if ((c < '0' || c > '9') && c != '.') break;
}
if (f2) t *= (f3 * decimal.Parse(expression.Substring(i, j - i)));
else t /= (f3 * decimal.Parse(expression.Substring(i, j - i)));
i = j;
goto g2;
}
else if (c == '(')
{
i++;
if (i >= expression.Length) goto exception;
if (f2) t *= (_Compute(expression, ref i) * f3);
else t /= (_Compute(expression, ref i) * f3);
if (i >= expression.Length) goto exception;
i++;
goto g2;
}
else if (char.IsWhiteSpace(c))
{
i++;
continue;
}
else goto exception;
}
goto exception;
}
else if (c == '(')
{
i++;
if (i >= expression.Length) goto exception;
if (f2) t *= _Compute(expression, ref i);
else t /= _Compute(expression, ref i);
if (i >= expression.Length) goto exception;
i++;
goto g2;
}
else if (char.IsWhiteSpace(c))
{
i++;
continue;
}
goto exception;
}
goto exception;
}
else if (c == ')') goto g2_end;
else if (char.IsWhiteSpace(c))
{
i++;
continue;
}
goto exception;
}
g2_end:
if (r.HasValue) return r.Value + f * t;
return f * t;
}