C++ Tutorial: Conditions and Loops

[GFreak45]

This tutorial uses: Functions and Variables and Getting Started

Conditions:

Conditions are essentially a question, with a true or false, yes or no answer. For instance, if the user says yes, then do this, else do something else. Variables/Functions returning a true/false are called booleans or bools for short. As well as the bool type, other types are used as conditions as well, if the byte-makeup of a value isnt equal to 0 then it returns true, otherwise it will return false. Common uses of conditions are if statements, ie:

if (some bool variable)
{
    do stuff for variable being true
}
else if (some other bool variable)
{
    do stuff for other variable being true
}
else
{
    do default option
}

which can also be written like so (if only one action is done per if statement):

if (some bool variable) do stuff for variable being true;
 
else if (some other bool variable) do stuff for other variable being true;
 
else do default option;

Another version of an if statement would be like so (if the return type of true and false actions are the same):

(some bool ? if true actions : if false actions)
ie:
(boolFunction() ? trueFunction() : falseFunction())

Conditional operators are as follows:

• == (equals) - if 2 values are equal to each other this returns true
• != (not equal) - if 2 values are not equal to each other this returns true
• !<bool value> (not) - if not true return true, if true return false
• > < (Greater than/Less than) - if the first value is greater than/less than the second return true
• >= <= (Greater than or equal to/Less than or equal to) - if the first value is greater than or equal to/less than or equal to, return true
• && (and) - if left side and right side of this operator are true, returns true
• || (or) - if the left side or right side of this operator are true, returns true

Another way of writing an if statement is with a switch statement (less efficient until you get into high ammounts of else ifs in one if statement) , ie:

unsigned int x = 0;
cin >> x;
switch (x)
{
    case 1:
        cout << "You input 1.\n";
        break;
    case 2:
        cout << "You input 2.\n";
        break;
    case 3:
        cout << "You input 3.\n";
        break;
    case 4:
        cout << "You input 4.\n";
        break;
    case 5:
        cout << "You input 5.\n";
        break;
    default:
        cout << "You input greater than 5.\n";
        break;
}

Note the breaks, those are required in switch statements, otherwise the next option will be run as well, for instance, if you delete the break just after case 1, then input 1, it will cout:
You input 1.
You input 2.
Switch statements check the variable they are called with for a value, and it will run based on the case that matches it, and unfortunately cases must be a constant value like 1 or 5, not a variable.

Loops:

Conditions are also used in loops, there are 3 commonly used types of loops, for loops, while loops, and do while loops.
while loops follow a format like so: while (bool is true) { do actions }, ie:

int x = 0;
while (x < 5)
{
    cout << "X is equal to: " << x << ".\n";
    x++;
}

which should output the following:
for loops follow this format: for (variable declaration; bool is true; action at end) { do actions }, ie:

for (int x = 0; x < 5; x++)
{
    cout << "X is equal to: " << x << ".\n";
}

do while loops follow this format: do { actions } while (bool is true);, ie:

int x = 0
do {
    cout << "X is equal to: " << x << ".\n";
    x++;
} while (x < 5);

The primary difference between a do while and a while loop is that a do while is run at least once regardless of the while condition.
The output for all of these loops should be the following:

X is equal to: 0
X is equal to: 1.
X is equal to: 2.
X is equal to: 3.
X is equal to: 4.

To wrap this up, lets write an application that requests a number from the user (1-100), then outputs whether the number is less than 50 or greater than 50, to challenge yourself allow the user to choose whether they want to continue by selecting 0.
This is how I would do it:

#include <iostream>
 
using namespace std;
 
int main ()
{
    int number = 0;
    cout << "Pick a number (1-100): ";
    cin >> number;
    while (number)
    {
        if (number <= 50) cout << "The number is less than or equal to 50.\n";
        else cout << "The number is greater than 50.\n";
        cout << "Pick a number (1-100): ";
        cin >> number;
    }
    cout << "\n";
    system("Pause");
    return 0;
}

 

[GetTriggerUnit-]

I would be really interested on a tutorial which explains how to handle unicode/utf8 in C/C++.

 

[GFreak45]

well i know the VC++ library has the System::String class which can handle unicode characters and automatically manages them for you, im not sure if the standard C++ library std::string class can do this but i believe it's parent class can, as its just a template class, ill look into it

Edit:
The std::string class handles utf8 the same way wc3 does (well almost) and it is possible to use std::basic_string<wchar> (wide char) for storing unicode but when using unicode-only characters it will cause errors in the display, apparently the boost library can handle the conversion from a wchar string to read-able unicode text

 

[GFreak45]

I just finished the string tutorial, you should read through it.