String and Int Conversion

Converting Between Strings and Ints

Video Summary: https://youtu.be/Fi8q3RQR6m0

Sometimes, you will have input in one format, such as a string, but you will want to do math with it as if it were an int. However, using addition on strings concatenates them, which is probably not your intention. Additionally, you can't just typecast a string to an int.

There are mutliple ways you could convert between the two, but the easiest is to use the built in functions in c++:

stoi (String TO Integer)
to_string

The following code demonstrates how to use these functions:

Which produces the following output:

Adding two strings together: 123321
Adding the strings converted to ints: 444
Converting back to strings: 123321

Exercise

Create a program that has the user enter 3 numbers on one line as a string. Break the string into three integers and add the result. Convert the result back into a string and concatenate it with a larger output string.

To read multiple words into one string, you will need to use getline(cin, stringName)
To break the string up, you will need to use a combination of stringName.find(space) and string.substr(startpos, endpos)
You will need to use stoi to convert each piece to an integer to add them
You will need to use to_string on the result, then add it to an output string

When you are finished, your output might look like this:

Enter three numbers then hit enter
1 2 3
The result is 6

Solution

/*
Program name: converting.cpp
Author: Devon Blewett
Purpose: This program prompts the user for three numbers, reads it as one string, divides the string into three integers and adds them together.  Finally, it converts the result back to a string and concatenates it into an output string.

Written for the Open Textbooks program
*/

#include <iostream>
#include <string.h>

using namespace std;

int main(){
    string input;
    int num1, num2, num3;
    int result;
    
    // prompt and read the starting string
    cout << "Enter three numbers then hit enter" <<endl;
    getline(cin, input);
    // find the first instance of ' ' 
    int pos = input.find(' ');
    // this creates a substring between the start and the first space, converts it into an integer, and assigns it to num1.  The result is the same as if you had split it into multiple steps
    num1 = stoi(input.substr(0, pos));
    // removes the first number from the input string plus the space
    input = input.substr(pos + 1);

// repeat process to remove second int
    pos = input.find(' ');
    num2 = stoi(input.substr(0, pos));
    // num3 will be whatever is left
    num3 = stoi(input.substr(pos + 1));

result = num1 + num2 + num3;
    // add the string version of result to an output string
    string output = "The result is " + to_string(result);

cout << output;
}

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