Question

need help to identify all the key components of a small program in cpp

Answer 1

can you please explain to me what's #include<iostream>, using namespace std,, and int main() do in simple and easy to remember words? thanks :)

Answer 2

you're using the functions cin and cout in your program, how does it know what cin and cout mean? It knows them because you've included the iostream header file which essentially tells what these functions are gonna do.
you won't be able to use the input/output functions if you don't #include<iostream>

Answer 3

what if i'm using void keyword? would i still need to type #include<iostream>??? Also i've seen ppl type #include, #include one after the other but won't type <iostream> wat's that fudge about ?

Answer 4

yep, you'd have to type #include<iostream> keyword if you're using void

```
void main(){
}
```
^this program won't work.

```
int main(){
return 0;
}
```
^but this will work

as long as you're using int as the return type it will work without typing #include<iostream>
but you'd need #include<iostream> for other important input output functions and much more

Answer 5

so all those keywords that we talked about come under iostream? :O
what the.....? :O and so for every input and output program, we'd need to include #include <iostream>
using namespace std;

Answer 6

btw is keywords and primitive data types both are the same thing correct?

Answer 7

wdym by the term 'keyword'?
are you referring to the data types like int, char, bool or you're referring to the function calls like cin, cout

Answer 8

so my textbook refers keywords to as things like bool, int, double, etc just wanted to make sure it's the same thing as primitive datatypes? same thing

Answer 9

All primitive data types can be used without typing #include<iostream> except for void
Also, if you're not typing #include<iostream> then you have to have your return type as int

Answer 10

omg that clears so many things lol thanks

Answer 11

also i need you to please help me understand what's a variable in a function... and please say it in simple words so it stick to my tiny brain. ;))))))))))))

Answer 12

int i, j;
char c;
bool b;

i, j, c, b are variables here. I can store whatever value I wish into them, so their values can change according to my needs, they're variables.

Answer 13

i'm going to print out this thread and stick it on my forehead... really informative and helpful :)))))))))))))))))))))))

Answer 14

```
using namespace std
```
to understand this you need to break it down into two parts because there are two things being used in here- 1)\(\color{purple}{using}\)
2)\(\color{blue}{namespace}\)

Answer 15

listening* :))))

Answer 16

this i didn't know ...very informative

Answer 17

\(\large\color{blue}{namespace}\)

Namespace helps you differentiate two things that might have the same name.
Kind of how the last name helps to differentiate two people having the same name

you can declare different namespaces in your program as I've done below-

```
#include<iostream>
using namespace std;

namespace first
{
int x = 1;
}

namespace second
{
int x = 2;
}

//Both namespaces have a variable named x

int main(){

//cout << x ----> this would be wrong because the reference to x is ambiguous

//how to refer to the x in namespace first?
//use first::
cout << "the x in namespace first is: " << first::x << endl;

//similarly
cout << "the x in namespace second is: " << second::x;
}
```

output:

```
the x in namespace first is: 1
the x in namespace second is: 2
```

Answer 18

ok 2 small questions... first is, if i'm working with a program that calculates the user's pay and under int main()
like this...
```
// This program calculates the user's pay.
#include <iostream>
using namespace std;

int main ()
{
//What is the programmer doing down here?? is he declaring the variables?
Double hours, rate, pay;

// Get the number of hours worked.
cout << "How many hours did you work?;
cin >> hours;

etc

Answer 19

the other question is that i've seen programmer use the #include #include commands but they don't include the #include<iostream> command in their program ???

Answer 20

\(\large\color{purple}{using}\)

everything in the iostream header file is in some namespace 'std'

but like in the above example you don't do `std::cin >> ` or `std::cout <<` you just directly do `cin >>` and `cout << `

That's because you've typed `using namespace std` in your program
whenever you do `using namespace std` you no longer have to deal with putting `std::` before everything which from inside the namespace std

```
#include<iostream>
//in this example we won't be typing using namespace std
// using namespace std;

namespace first
{
int x = 1;
}

namespace second
{
int x = 2;
}
//Both namespaces have a variable named x

//we're using namespace first
using namespace first;
int main(){

//how to refer to the x in namespace first?
std::cout << "the x in namespace first is: " << x << std::endl;

//how to refer to the x in namespace second?
//you'd have to use second::
std::cout << "the x in namespace second is: " << second::x;
}
```

Problem with `using namespace` :
you can't type `using namespace first` and `using namespace second` together
because then if you do `cout << x` the reference to x would be ambiguous.

Answer 21

\(\color{#0cbb34}{\text{Originally Posted by}}\) @Ballery1
ok 2 small questions... first is, if i'm working with a program that calculates the user's pay and under int main()
like this...
```
// This program calculates the user's pay.
#include <iostream>
using namespace std;

int main ()
{
//What is the programmer doing down here?? is he declaring the variables?
Double hours, rate, pay;

// Get the number of hours worked.
cout << "How many hours did you work?;
cin >> hours;

etc
```
\(\color{#0cbb34}{\text{End of Quote}}\)
it should be *double
yes, he is declaring some variables of the data type double```

Answer 22

i see now.. what about the second thing.. why do programmers just use #include #include and move on with the rest of the code rather than do #include<iostream>??

Answer 23

you sure it was `#include #include`? because that would throw an error

whenever you do `#include` you need to give a filename after it
like `#include<iostream>`

Answer 24

```
#include
#include

int main ()

etc

Answer 25

i wish i could find an example rn. i'm drowning with papers over here .

Answer 26

\(\color{#0cbb34}{\text{Originally Posted by}}\) @Ballery1
```
#include
#include

int main ()

etc
```
\(\color{#0cbb34}{\text{End of Quote}}\)

output:
```
prog.cpp:1:10: error: #include expects "FILENAME" or <FILENAME>
prog.cpp:2:9: error: #include expects "FILENAME" or <FILENAME>
```

Answer 27

they probably forgot what to include and left it blank?

Answer 28

sorry i didn't give you the whole thing but that's the gist of it... i'll let you know when i find it.

Answer 29

aight

Answer 30

no it was a proper thing program

Answer 31

omg i forgot about the most important question......oof how do you store an input into the memory?? so for instance i'm working on a account balance and in my pseudocode, i wrote how much credit do they have? then they'd type in their credit. then the program would save that info in the memory and then ask them how much do they wanna take it out of their account and store that info and in the end, the program would just subtract their current balance with the amount they took out and show the remainder on the screen. so how do you store an input into the memory again ?

Answer 32

again, i saw these examples somewhere in the textbook but sadly can't find them rn :/

Answer 33

declare some variables and store the values in them

Answer 34

that's what variables are for, to store values

Answer 35

can you please show a tiny exaple ? :))))))))))))))))))))))))))))))))))))))))))

Answer 36

cuz i'm having trouble with the fact that do i need to declare some digit to store that info or what ??? like how we add numbers and stuf

Answer 37

```
#include<iostream>
using namespace std;


int main(){
double credit, withdraw;

cout << "Enter your current credit: ";
cin >> credit;

cout << endl;

cout<< "Enter the withdraw amount: ";
cin >> withdraw;

cout << endl;

//update the credit

credit = credit - withdraw;

cout << "Your new credit: " << credit << endl;
}
```

Answer 38

you can use the normal +, -, /, * operators to do math operations

Answer 39

so anything under cout and cin is automatically being stored into the memory?

Answer 40

not exactly

Answer 41

so inside those pointy brackets then??? << and >>

Answer 42

cout is only used to output something
you use cout whenever you want to display something on the screen

cin is used when you want to take in some input from the user
whenever you take in input you have to use a variable to store it in

Answer 43

ok so how do i know what's being stored into the memory tho ??? :/ so when i write my own code i'd know that variable a + b = c will be stored into the memory :/

Answer 44

i want the value of c stored into the memory.

Answer 45

just show me one tiny example that's all

Answer 46

you want c to be a+b

there a difference between c = a + b and a + b = c

the thing on the left-hand side is supposed to represent the place where you store the value of the expression on the right-hand side

the correct way will be c = a + b

Declare three variables a,b, c
every variable represents some location in your memory
all the variables are stored in the memory somewhere

when you do cout << a
it will access the location in memory which has belongs to the variable a and print the value inside it

after declaring the variables you need to take input from the user and store it in them
cin >> a >> b
^took input from the user and stored it in a and b
so the memory locations associated with a and b now have some values which were provided by the user

c = a+b

it computes a + b and stores that value in the memory location associated with the variable c

Answer 47

ok this makes sense. again, thank you soooooooooo much for you help. really appreciated <3 :))))))))))))))))))))))

Answer 48

np