Thread: Simple Function program, with Strings?

I am using O'reilly's Practical C++ Programming book in its 2nd edition. I have to create a program to complete the following question:

Write a function begins(string1, string2) that returns true if string1 begins string2.

This was confusing to me at first, and I think poorly written. From what I understand, I need to write a program that inputs a first string, and then a second string. Then, I guess it should input a third string - containing both first and second strings in any order - and then output true or false depending on the order..

As an example: Enter your first name, Enter your last name, Enter your Full name (either firstname first or firstname last), and then output true or false depending on the circumstances.., etc. I assume I can use a IF statment to determine the order of the strings..?

Please let me know if my grasp on the question is correct, or if I am way off.

I have the code started, and need some help - but I wanted to make sure I was approaching the question correctly before I flood the thread with questions


Thanks all =)

Ok, got it. I knew I was interpreting it incorrectly.

What control statment is reccommended to search a string for another string??

Heres where I am at:

Code:

#include <iostream>
#include <string>


std::string input1;     //First string
std::string input2;     //Second string

int main()
{

std::string begins(std::string string1, std::string string2);  //Declares Function

std::cout << "Please enter the first string: ";
std::getline(std::cin, input1);         //Gets first string

std::cout << "Please enter the second string: ";
std::getline(std::cin, input2);         //Gets second string


begins(input1, input2);  // Calls Function

void begins(std::string string1, std::string string2)
{
                //Will Contain control statments to determine if input1 contains input2
}


return (0);
}

Thanks all

Big hint: Look at std::equal

First off, thanks everyone for their input thus far..

Heres how I want to handle this..

Two strings are inputted, I need to see if the first string begins the second string (hell, hello = true)

Anyway.. Heres what I think I need to do..

1. Get the length of the first string

Code:

length = std::strlen(input1)

2. Copy string 2 using only the number determined by length from above.

Code:

std::strncpy(string2, string1, length)

3. Use strcmp to compare the two inputted strings.

Code:

std::strcmp(string, string2)

4. Use an IF statement that returns TRUE if the strings match, and FALSE if otherwise..

Is this the correct way of tackling this program??

thx all

That looks like a good way to do it, but you shouldn't be using strlen, strncpy and strcmp since those are for C style strings. Your program above uses the C++ string class, so you would use length(), substr(), and ==.

Also be careful to handle the case when the first string is longer than the second.

I'd use the substr method rather than copy.

Ok, when I try to use substr, heres what I get:

Code:

#include <iostream>
#include <string>


std::string input1;     //First string
std::string input2;     //Second string
int length;
std::string crop;       //Second string, cropped to same length as first string

int main()
{


std::cout << "Please enter the first string: ";
std::getline(std::cin, input1);         //Gets first string

std::cout << "Please enter the second string: ";
std::getline(std::cin, input2);         //Gets second string



length = input1.length();
crop = input2.substr(length);

std::cout << "Length: " << length << '\n';
std::cout << "input 2 cropped = " << crop << '\n';

return (0);
}

The program DOES compile correctly without errors. For the first string, I enter "hell", and for the second string I enter "hello".. It says the first string is length 4 (correct), but then it outputs "o". Its simply taking 4 chars off the beginning of the second string. I need it to crop them from the end.

If the first strings 4 long, I need to make string 2 (no matter how long) just the first 4 chars. From here I will use a == IF statement to compare.

How do I use substr to remove all chars except the defined beginning length?

thank you =)

The first parameter of substr is the the index of the first character you want to include in your substring. So when you used 4 on the string hello, you start with the letter 'o' ('h' is index 0, 'e' is 1, 'l' is 2, 'l' is 3 and 'o' is 4).

So change that first parameter to the index of the first character you want to include.

It is the second parameter to substr that is the number of characters you want.

This should take a single line of code, people:

Code:

if(string1.size() <= string2.size() && std::equal(string1.begin(), string1.end(), string2.begin()))
    // it matches

This is an exercise to see if the OP can figure out how to solve the problem, not to see what the "best way" is.

Originally Posted by Daved

This is an exercise to see if the OP can figure out how to solve the problem, not to see what the "best way" is.

If the intention is to comprehend how to manipulate the individual characters of strings, then I think the exercise is quite bizarre, since the entire point of std::string is to insulate you from the representation of the string as a sequence of characters.

In other words, making people "look inside" a std::string only teaches them that that's the right way to deal with strings, and it's not (at least in C++).