break statements in c++

Atreides

Right I wrote this program to take any date for any year greater then 1800 and output the day. Program does that grand. Things is Where i use break statement I want to also be able to cout<<"This is not a real date"<<endl; except it won't let me, is there a way around it.

[PHP] #include <iostream>
#include <string>
using namespace std;
int leap(int year);
int offset(int yy);
int main()
{ int dd,mm,yyyy, date[] = {0, 31, 0, 31, 30, 31, 30, 31, 31, 30, 31, 30};
string day[] = {" ","wednesday","Thursday","Friday","saturday","sunday","monday","tuesday",};
while (true)
{
cout<<"Enter The date or 0 to exist: \n";
cin >>dd>>mm>>yyyy;
if ((dd == 0) || (dd > 31) || (mm > 12))break;
if((leap(yyyy) == true))
date[2] = 29;
else date[2] = 28;

if((dd > date[mm]) || (dd < 0))break;
for (int i = 0; mm > i; i++)
{dd += date;}
dd = (dd + offset(yyyy))%7;

cout<<"The day on the: "<<dd<<"/"<<mm<<"/"<<yyyy<<" is: "<<day[dd]<<endl;
}
return 0;
}
int leap(int year)
{ if ((year%400 == 0) || ((year%4 ==0) && (year%100 != 0)))
return true;
else
return false;
}
int offset(int yy)
{int Total_days = 0;
for (int base = 1800; base != yy;base++)
{
if((leap(base) == true))
Total_days += 366;
else {Total_days += 365;}
}
return (Total_days%7);
}[/PHP]

Silent Bob

replace this

if ((dd == 0) || (dd > 31) || (mm > 12))break;

with some scoping indicators, like this

if ((dd == 0) || (dd > 31) || (mm > 12))
{
    cout << "stuff" << endl;
    break;
}

and you will be fine.

Except that you use integers for your dd/mm/yyyy variables and don't check properly for the cases where the user inputs negative values, using unsigned ints instead would be a good thing.

[edit] Why this works:
You are only allowed to have a single statement after an if statement, this is why

if(condition)
    cout << "blah" << endl;
    break;

will always break, only the cout is covered by the if statement

If you use curly braces though you are telling the compiler that there is a statement block between those matching braces that is covered by the if statement, so

if(condition)
{
    cout << "blah" << endl;
    break;
}

causes both the cout and the break to happen when condition is true.

Atreides

Hmm I tried that and it kept closing on me, then i realised it was working just happening so fast dos was closing.

what do you mean be usign unsigned ints however

Silent Bob

There are two types of integer in C++. A signed integer (int) and unsigned integers (unsigned int). Signed integers can have a positive or negative value an unsigned integer will always be interpreted as having a positive value (counting 0 as positive:))

If you have variables that represent things which shouldn't ever be negative you should use unsigned integers for them (this is the case generally, sometimes with loop counters you need to be careful). Using an unsigned int means you only have to check if the number input by the user (or whatever) is less than it's upper bound, you don't have to check if it is less than 0.

Take your check on dd

if ((dd == 0) || (dd > 31) || (mm > 12))break;

Here you check if the day is equal to zero or greater than 31 and break if it is either of these.

This would be fine with unsigned ints but because dd is a signed int there is another case where it can be less than 0.

Atreides

Hmm I've taken care of the possibility now. What would happen if someone entered an negative number to an unsigned int, would itjust take the absolute value? If so that would be very handy.

Silent Bob

Originally posted by Skanger
Hmm I've taken care of the possibility now. What would happen if someone entered an negative number to an unsigned int, would itjust take the absolute value? If so that would be very handy.

It won't take the absolute value. I haven't looked at the iostream source so I can't confirm this, but if iostream reads "-2" as a negative integer and then assigns to an unsigned int the unsigned int will contain the value associated with the bit pattern of the negative int.
This of course is based on iostream reading "-2" as -2 when it knows it is assigning to an unsigned integer.

Given that most architectures these days use two's complement signed integer systems this will mean that a value of -1 will, in fact, be interpreted as 4294967295.