help understanding strings in c++

**newbc** · 06-29-2011

ok so I just stiched from c to c++ and im having problems using strings for some of my functions. this is my code

Code:

#include <iostream>

using namespace std;

int main() {
  string item;

  while (cin >> item) {
    cout << item << endl;
    }

  return 0;
}

say i enter this info to it (in one line then press enter):
1 2 3 4 5 + - display 12 *

I get this

Code:

1 2 3 4 5 + - display 12 * delete
1
2
3
4
5
+
-
display
12
*
delete

now this is the part where im not understanding how to put it in code. Our teacher wants us do an add numbers to a stack and add or subtract some numbers is when enter the signs (+ -). I cant think of a way to do it. I just need help thinking not asking for you guys to do my homework just some enlightenment.

thank you for reading.

for like the one that is enter here how would I do this function to add a one(1) to the stack? how can it differentiate from letters and numbers?
can I do some thing like this?

Code:

while (cin >> item) {
   
 if (item == int){
  add number one to stack;
 }

 if (item== "delete" ignoring capitalization)
  delete all the items from stack
 }


 }

}

**tabstop** · 06-29-2011

I'm not sure that this is a string question, but a stack question. Do you know how to put anything on a stack? Do you know how to take things off a stack? Are you supposed to use the stack that's in C++ or write your own?

**newbc** · 06-29-2011

Originally Posted by tabstop

I'm not sure that this is a string question, but a stack question. Do you know how to put anything on a stack? Do you know how to take things off a stack? Are you supposed to use the stack that's in C++ or write your own?

yes i do know how to put items in stack. what im having problems is taking the input like 1 2 3 in the same line and adding them to a stack using a function. Im used to doing it one in put per line not multiple like this. because later my program needs to delete all the items in a stack if the user types delete.

**tabstop** · 06-29-2011

So put your stack input in your loop (perhaps in place of printing it to the screen) and you're done.

**newbc** · 06-29-2011

so i'm reading online and find a way to compare strings.

if (user1.compare(user) == 0)

just some questions is this case sensitive? or is Delete not the same as delete? any help on figuring out how to ignore capital letter?

**laserlight** · 06-29-2011

Originally Posted by newbc

if (user1.compare(user) == 0)

just some questions is this case sensitive? or is Delete not the same as delete?

Yes, case sensitive. You could have checked it youself. Incidentally, it is more common to write:

Code:

if (user1 == user)

Originally Posted by newbc

any help on figuring out how to ignore capital letter?

Convert both strings to uppercase or lowercase.

**newbc** · 06-29-2011

thanks for the help laserlight

lets say I want to check if the character is an int how would do that i found a function online to convert a string to int
, but im having a problem checking the string value using an if statement.

since I'm asking them to enter characters how would do an if statement to check it?

Code:

string item;

if (item = a number){
 do this
}

**laserlight** · 06-29-2011

Originally Posted by newbc

lets say I want to check if the character is an int how would do that i found a function online to convert a string to int

We call the above a run-on sentence. Calm down and elaborate on what exactly it is you want to check. It may help to provide an example.

**newbc** · 06-30-2011

Originally Posted by laserlight

We call the above a run-on sentence. Calm down and elaborate on what exactly it is you want to check. It may help to provide an example.

lets say I'm using the first example I posted on top. Since it saves everything as characters, how can I know if the character is actually a number? using an if statement.
The user then enters this data: 1 car 2
so now it needs to check if 1 and 2 are actually ints.

Code:

#include <iostream>

using namespace std;

int main() {
  string item;

  while (cin >> item) {
    
   if (item = a number){
     do this
   }

    }

  return 0;
}

Basically how do i check if the character is an int?

**tabstop** · 06-30-2011

That is what isdigit is for. There's also isalpha, isupper, islower, and lots of things that live in <cctype>.

**newbc** · 06-30-2011

Originally Posted by tabstop

That is what isdigit is for. There's also isalpha, isupper, islower, and lots of things that live in <cctype>.

thank u I knew I read it somewhere but I could not find it online. thanks. I guess this works for both c and c++ right?

**Elysia** · 06-30-2011

It does, but they want a C-style string. So if you have a std::string, call the c_str() member function to get a C-style string to pass to those functions.

**King Mir** · 06-30-2011

It might be easier to do this:

Code:

double number 
if(cin >> number){
  //do number stuff
} else {
  cin.clear(ios::failbit);
  if(cin >> str){
    //do operator stuff
  }
}

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