Converting string to number and vice-versa in C++

In this section we will see how to convert string to number and number to string. At first we will see how to convert string to number.

String to Number Conversion

Here we will see how to convert a number string to integer type data. We can solve this problem by using the atoi() function. This function takes string as input and converts into integer data.

The atoi() function is present in the <cstdlib> library.

Input: A number string “1234”
Output: 1234

Algorithm

Step 1:Take a number string
Step 2: Convert it to integer using atoi() function
Step 3: Print the result.
Step 4: End

Example Code

 Live Demo

#include<iostream>
#include<cstdlib>
using namespace std;
main() {
   int n;
   char num_string[20] = "1234";
   n = atoi(num_string);
   cout << n;
}

Output

1234

Number to String Conversion

In this section we will see how to convert a number (integer or float or any other numeric type data) to a string.

The logic is very simple. Here we will use the sprintf() function. This function is used to print some value or line into a string, but not in the console. This is the only difference between printf() and sprintf(). Here the first argument is the string buffer. where we want to save our data.

Input: User will put some numeric value say 42.26
Output: This program will return the string equivalent result of that number like “42.26”

Algorithm

Step 1: Take a number from the user
Step 2: Create an empty string buffer to store result
Step 3: Use sprintf() to convert number to string
Step 4: End

Example Code

 Live Demo

#include<stdio.h>
main() {
   char str[20]; //create an empty string to store number
   float number;
   printf("Enter a number: ");
   scanf("%f", &number);
   sprintf(str, "%f", number);//make the number into string using sprintf function
   printf("You have entered: %s", str);
}

Output

Enter a number: 46.3258
You have entered: 46.325802