Post: Few thing's to learn in C++ (LESSON 3 Completed)
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09-12-2015, 10:30 PM
#1
K3-
Bounty hunter
Hey NGU to im going to be writing out a few thing in C++ maybe adding more stuff daily or when i can be botherd and ain't busy 
If you want to add something to this PM me.
If you want to add something to this PM me.
Lesson 1, Loop's
One Caveat: before going further, you should understand the concept of C++'s true and false, because it will be necessary when working with loops (the conditions are the same as with if statements). There are three types of loops: for, while, and do..while. Each of them has their specific uses. They are all outlined below.
FOR - for loops are the most useful type. The syntax for a for loop is
for ( variable initialization; condition; variable update ) {
Code to execute while the condition is true
}
The variable initialization allows you to either declare a variable and give it a value or give a value to an already existing variable. Second, the condition tells the program that while the conditional expression is true the loop should continue to repeat itself. The variable update section is the easiest way for a for loop to handle changing of the variable. It is possible to do things like x++, x = x + 10, or even x = random ( 5 ), and if you really wanted to, you could call other functions that do nothing to the variable but still have a useful effect on the code. Notice that a semicolon separates each of these sections, that is important. Also note that every single one of the sections may be empty, though the semicolons still have to be there. If the condition is empty, it is evaluated as true and the loop will repeat until something else stops it.
Example:
#include <iostream>
using namespace std; // So the program can see cout and endl
int main()
{
// The loop goes while x < 10, and x increases by one every loop
for ( int x = 0; x < 10; x++ ) {
// Keep in mind that the loop condition checks
// the conditional statement before it loops again.
// consequently, when x equals 10 the loop breaks.
// x is updated before the condition is checked.
cout<< x <<endl;
}
cin.get();
}
This program is a very simple example of a for loop. x is set to zero, while x is less than 10 it calls cout<< x <<endl; and it adds 1 to x until the condition is met. Keep in mind also that the variable is incremented after the code in the loop is run for the first time.
WHILE - WHILE loops are very simple. The basic structure is
while ( condition ) { Code to execute while the condition is true } The true represents a boolean expression which could be x == 1 or while ( x != 7 ) (x does not equal 7). It can be any combination of boolean statements that are legal. Even, (while x ==5 || v == 7) which says execute the code while x equals five or while v equals 7. Notice that a while loop is the same as a for loop without the initialization and update sections. However, an empty condition is not legal for a while loop as it is with a for loop.
Example:
#include <iostream>
using namespace std; // So we can see cout and endl
int main()
{
int x = 0; // Don't forget to declare variables
while ( x < 10 ) { // While x is less than 10
cout<< x <<endl;
x++; // Update x so the condition can be met eventually
}
cin.get();
}
This was another simple example, but it is longer than the above FOR loop. The easiest way to think of the loop is that when it reaches the brace at the end it jumps back up to the beginning of the loop, which checks the condition again and decides whether to repeat the block another time, or stop and move to the next statement after the block.
DO..WHILE - DO..WHILE loops are useful for things that want to loop at least once. The structure is
do {
} while ( condition );
Notice that the condition is tested at the end of the block instead of the beginning, so the block will be executed at least once. If the condition is true, we jump back to the beginning of the block and execute it again. A do..while loop is basically a reversed while loop. A while loop says "Loop while the condition is true, and execute this block of code", a do..while loop says "Execute this block of code, and loop while the condition is true".
Example:
#include <iostream>
using namespace std;
int main()
{
int x;
x = 0;
do {
// "Hello, world!" is printed at least one time
// even though the condition is false
cout<<"Hello, world!\n";
} while ( x != 0 );
cin.get();
Or you can use "system(pause);" over "cin.get():"
}
Thanks to Mango_Knife
Keep in mind that you must include a trailing semi-colon after the while in the above example. A common error is to forget that a do..while loop must be terminated with a semicolon (the other loops should not be terminated with a semicolon, adding to the confusion). Notice that this loop will execute once, because it automatically executes before checking the condition.
Lesson 2, Function's
For example:
include <cstdlib> // Include rand()
using namespace std; // Make rand() visible
int a = rand(); // rand is a standard function that all compilers have
Do not think that 'a' will change at random, it will be set to the value returned when the function is called, but it will not change again.
The general format for a prototype is simple like i've written below;
return-type function_name ( arg_type arg1, ..., arg_type argN );
arg_type just means the type for each argument -- for instance, an int, a float, or a char. It's exactly the same thing as what you would put if you were declaring a variable.
There can be more than one argument passed to a function or none at all (where the parentheses are empty), and it does not have to return a value. Functions that do not return values have a return type of void. Let's look at a function prototype:
int mult ( int x, int y );
This prototype specifies that the function mult will accept two arguments, both integers, and that it will return an integer. Do not forget the trailing semi-colon. Without it, the compiler will probably think that you are trying to write the actual definition of the function.
When the programmer actually defines the function, it will begin with the prototype, minus the semi-colon. Then there should always be a block with the code that the function is to execute, just as you would write it for the main function. Any of the arguments passed to the function can be used as if they were declared in the block. Finally, end it with a closing brace.
example:
include <iostream>
using namespace std;
int mult ( int x, int y );
int main()
{
int x;
int y;
cout<<"Please input two numbers to be multiplied: ";
cin>> x >> y;
cin.ignore();
cout<<"The product of your two numbers is "<< mult ( x, y ) <<"\n";
cin.get();
}
int mult ( int x, int y )
{
return x * y;
}
This program begins with the only necessary include file and a directive to make the std namespace visible. Everything in the standard headers is inside of the std namespace and not visible to our programs unless we make them so. Next is the prototype of the function. Notice that it has the final semi-colon! The main function returns an integer, which you should always have to conform to the standard. You should not have trouble understanding the input and output functions. It is fine to use cin to input to variables as the program does. But when typing in the numbers, be sure to separate them by a space so that cin can tell them apart and put them in the right variables.
Notice how cout actually outputs what appears to be the mult function. What is really happening is cout is printing the value returned by mult, not mult itself. The result would be the same as if we had use this print instead
cout<<"The product of your two numbers is "<< x * y <<"\n";
The mult function is actually defined below main. Due to its prototype being above main, the compiler still recognizes it as being defined, and so the compiler will not give an error about mult being undefined. As long as the prototype is present, a function can be used even if there is no definition. However, the code cannot be run without a definition even though it will compile. The prototype and definition can be combined into one also. If mult were defined before it is used, we could do away with the prototype because the definition can act as a prototype as well.
Return is the keyword used to force the function to return a value. Note that it is possible to have a function that returns no value. If a function returns void, the return statement is valid, but only if it does not have an expression. In other words, for a function that returns void, the statement "return;" is legal, but redundant.
The most important functional (Pun semi-intended) question is why do we need a function? Functions have many uses. For example, a programmer may have a block of code that he has repeated forty times throughout the program. A function to execute that code would save a great deal of space, and it would also make the program more readable. Also, having only one copy of the code makes it easier to make changes. Would you rather make forty little changes scattered all throughout a potentially large program, or one change to the function body? So would I.
Another reason for functions is to break down a complex program into logical parts. For example, take a menu program that runs complex code when a menu choice is selected. The program would probably best be served by making functions for each of the actual menu choices, and then breaking down the complex tasks into smaller, more manageable tasks, which could be in their own functions. In this way, a program can be designed that makes sense when read. And has a structure that is easier to understand quickly. The worst programs usually only have the required function, main, and fill it with pages of jumbled code.
Lesson 3, switch case in C and C++
switch ( <variable> ) {
case this-value:
Code to execute if <variable> == this-value
break;
case that-value:
Code to execute if <variable> == that-value
break;
...
default:
Code to execute if <variable> does not equal the value following any of the cases
break;
}
The condition of a switch statement is a value. The case says that if it has the value of whatever is after that case then do whatever follows the colon. The break is used to break out of the case statements. Break is a keyword that breaks out of the code block, usually surrounded by braces, which it is in. In this case, break prevents the program from falling through and executing the code in all the other case statements. An important thing to note about the switch statement is that the case values may only be constant integral expressions. Sadly, it isn't legal to use case like this:
int a = 10;
int b = 10;
int c = 20;
switch ( a ) {
case b:
// Code
break;
case c:
// Code
break;
default:
// Code
break;
}
The default case is optional, but it is wise to include it as it handles any unexpected cases. Switch statements serves as a simple way to write long if statements when the requirements are met. Often it can be used to process input from a user.
Below is a sample program, in which not all of the proper functions are actually declared, but which shows how one would use switch in a program.
include <iostream>
using namespace std;
void playgame()
{
cout << "Play game called";
}
void loadgame()
{
cout << "Load game called";
}
void playmultiplayer()
{
cout << "Play multiplayer game called";
}
int main()
{
int input;
cout<<"1. Play game\n";
cout<<"2. Load game\n";
cout<<"3. Play multiplayer\n";
cout<<"4. Exit\n";
cout<<"Selection: ";
cin>> input;
switch ( input ) {
case 1: // Note the colon, not a semicolon
playgame();
break;
case 2: // Note the colon, not a semicolon
loadgame();
break;
case 3: // Note the colon, not a semicolon
playmultiplayer();
break;
case 4: // Note the colon, not a semicolon
cout<<"Thank you for playing!\n";
break;
default: // Note the colon, not a semicolon
cout<<"Error, bad input, quitting\n";
break;
}
cin.get();
}
This program will compile, but cannot be run until the undefined functions are given bodies, but it serves as a model (albeit simple) for processing input. If you do not understand this then try mentally putting in if statements for the case statements. Default simply skips out of the switch case construction and allows the program to terminate naturally. If you do not like that, then you can make a loop around the whole thing to have it wait for valid input. You could easily make a few small functions if you wish to test the code.
Last edited by
K3- ; 09-16-2015 at 09:44 PM.
The following user thanked K3- for this useful post:
09-14-2015, 08:05 AM
#3
Mango_Knife
In my man cave
Originally posted by K3
Hey NGU to im going to be writing out a few thing in C++ maybe adding more stuff daily or when i can be botherd and ain't busy
Lesson 1, Loop's
Loops are used to repeat a block of code. Being able to have your program repeatedly execute a block of code is one of the most basic but useful tasks in programming -- many programs or websites that produce extremely complex output (such as a message board) are really only executing a single task many times. (They may be executing a small number of tasks, but in principle, to produce a list of messages only requires repeating the operation of reading in some data and displaying it.) Now, think about what this means: a loop lets you write a very simple statement to produce a significantly greater result simply by repetition.
One Caveat: before going further, you should understand the concept of C++'s true and false, because it will be necessary when working with loops (the conditions are the same as with if statements). There are three types of loops: for, while, and do..while. Each of them has their specific uses. They are all outlined below.
FOR - for loops are the most useful type. The syntax for a for loop is
The variable initialization allows you to either declare a variable and give it a value or give a value to an already existing variable. Second, the condition tells the program that while the conditional expression is true the loop should continue to repeat itself. The variable update section is the easiest way for a for loop to handle changing of the variable. It is possible to do things like x++, x = x + 10, or even x = random ( 5 ), and if you really wanted to, you could call other functions that do nothing to the variable but still have a useful effect on the code. Notice that a semicolon separates each of these sections, that is important. Also note that every single one of the sections may be empty, though the semicolons still have to be there. If the condition is empty, it is evaluated as true and the loop will repeat until something else stops it.
Example:
This program is a very simple example of a for loop. x is set to zero, while x is less than 10 it calls cout<< x <<endl; and it adds 1 to x until the condition is met. Keep in mind also that the variable is incremented after the code in the loop is run for the first time.
WHILE - WHILE loops are very simple. The basic structure is
while ( condition ) { Code to execute while the condition is true } The true represents a boolean expression which could be x == 1 or while ( x != 7 ) (x does not equal 7). It can be any combination of boolean statements that are legal. Even, (while x ==5 || v == 7) which says execute the code while x equals five or while v equals 7. Notice that a while loop is the same as a for loop without the initialization and update sections. However, an empty condition is not legal for a while loop as it is with a for loop.
Example:
This was another simple example, but it is longer than the above FOR loop. The easiest way to think of the loop is that when it reaches the brace at the end it jumps back up to the beginning of the loop, which checks the condition again and decides whether to repeat the block another time, or stop and move to the next statement after the block.
DO..WHILE - DO..WHILE loops are useful for things that want to loop at least once. The structure is
Notice that the condition is tested at the end of the block instead of the beginning, so the block will be executed at least once. If the condition is true, we jump back to the beginning of the block and execute it again. A do..while loop is basically a reversed while loop. A while loop says "Loop while the condition is true, and execute this block of code", a do..while loop says "Execute this block of code, and loop while the condition is true".
Example:
Keep in mind that you must include a trailing semi-colon after the while in the above example. A common error is to forget that a do..while loop must be terminated with a semicolon (the other loops should not be terminated with a semicolon, adding to the confusion). Notice that this loop will execute once, because it automatically executes before checking the condition.
Lesson 1, Loop's
One Caveat: before going further, you should understand the concept of C++'s true and false, because it will be necessary when working with loops (the conditions are the same as with if statements). There are three types of loops: for, while, and do..while. Each of them has their specific uses. They are all outlined below.
FOR - for loops are the most useful type. The syntax for a for loop is
for ( variable initialization; condition; variable update ) {
Code to execute while the condition is true
}
The variable initialization allows you to either declare a variable and give it a value or give a value to an already existing variable. Second, the condition tells the program that while the conditional expression is true the loop should continue to repeat itself. The variable update section is the easiest way for a for loop to handle changing of the variable. It is possible to do things like x++, x = x + 10, or even x = random ( 5 ), and if you really wanted to, you could call other functions that do nothing to the variable but still have a useful effect on the code. Notice that a semicolon separates each of these sections, that is important. Also note that every single one of the sections may be empty, though the semicolons still have to be there. If the condition is empty, it is evaluated as true and the loop will repeat until something else stops it.
Example:
#include <iostream>
using namespace std; // So the program can see cout and endl
int main()
{
// The loop goes while x < 10, and x increases by one every loop
for ( int x = 0; x < 10; x++ ) {
// Keep in mind that the loop condition checks
// the conditional statement before it loops again.
// consequently, when x equals 10 the loop breaks.
// x is updated before the condition is checked.
cout<< x <<endl;
}
cin.get();
}
This program is a very simple example of a for loop. x is set to zero, while x is less than 10 it calls cout<< x <<endl; and it adds 1 to x until the condition is met. Keep in mind also that the variable is incremented after the code in the loop is run for the first time.
WHILE - WHILE loops are very simple. The basic structure is
while ( condition ) { Code to execute while the condition is true } The true represents a boolean expression which could be x == 1 or while ( x != 7 ) (x does not equal 7). It can be any combination of boolean statements that are legal. Even, (while x ==5 || v == 7) which says execute the code while x equals five or while v equals 7. Notice that a while loop is the same as a for loop without the initialization and update sections. However, an empty condition is not legal for a while loop as it is with a for loop.
Example:
#include <iostream>
using namespace std; // So we can see cout and endl
int main()
{
int x = 0; // Don't forget to declare variables
while ( x < 10 ) { // While x is less than 10
cout<< x <<endl;
x++; // Update x so the condition can be met eventually
}
cin.get();
}
This was another simple example, but it is longer than the above FOR loop. The easiest way to think of the loop is that when it reaches the brace at the end it jumps back up to the beginning of the loop, which checks the condition again and decides whether to repeat the block another time, or stop and move to the next statement after the block.
DO..WHILE - DO..WHILE loops are useful for things that want to loop at least once. The structure is
do {
} while ( condition );
Notice that the condition is tested at the end of the block instead of the beginning, so the block will be executed at least once. If the condition is true, we jump back to the beginning of the block and execute it again. A do..while loop is basically a reversed while loop. A while loop says "Loop while the condition is true, and execute this block of code", a do..while loop says "Execute this block of code, and loop while the condition is true".
Example:
#include <iostream>
using namespace std;
int main()
{
int x;
x = 0;
do {
// "Hello, world!" is printed at least one time
// even though the condition is false
cout<<"Hello, world!\n";
} while ( x != 0 );
cin.get();
}
Keep in mind that you must include a trailing semi-colon after the while in the above example. A common error is to forget that a do..while loop must be terminated with a semicolon (the other loops should not be terminated with a semicolon, adding to the confusion). Notice that this loop will execute once, because it automatically executes before checking the condition.
Nice, you can also use "system("pause");" instead of cin.get();
But when, i think it's a bit useless because people can look for C tutorials on youtube..
09-14-2015, 09:03 PM
#8
Mango_Knife
In my man cave
03-23-2016, 01:49 AM
#9
Jim Halpert
Bounty hunter
Originally posted by Knife
Nice, you can also use "system("pause");" instead of cin.get();
But when, i think it's a bit useless because people can look for C tutorials on youtube..
But when, i think it's a bit useless because people can look for C tutorials on youtube..
system commands like that are bad to use because they are for Windows only. std::cin.get() is compatible with any OS as it's part of the standard library.
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