May 21, 2010

String to integer c++

By Mohammed Abualrob Algorithms and Data Structures 0 Comments

String to integer in c++

Given an integer number in string format, for example “12345”. Write a program or function to convert a string to integer in C without using library.

String to integer algorithm

Loop through the characters of the string representing the integer number. Get the integer value of the current digit by subtracting the ASCII code of ‘0’ from the ASCII code of the current character. Multiply that number by 10 raised to the power of the position of that digit in the string. Keep adding those values until all characters are scanned.

Example code

Here is a C++ code to do that

//Includes
#include <iostream>
using namespace std;
 
void main()
{
   //Input number in string format
   char numStr[] = "12345";

   //Integer value of the number string
   //to be calculated
   int numInt = 0;

   //Find string length. You can use a built in function
   //but we are calculating the length manually.
   int len = 0;
   while (numStr[len] != '\\0') len++;

   //This is needed to calculate powers of 10
   int power = 1;

   //Loop in the string character by character
   //Get the current digit by subtracting the ASCII code of '0'
   //from its ASCII code. You need to cast the rest to integer
   //type. Then multiply the result by 10 raised to a power equal
   //to the position of the character from right to left starting
   //the count from 0. For example 2 in the example above has 
   //position 2
   for (int i = len-1; i >= 0; i--)
   {
      numInt += (int)(numStr[i]-'0') * power;
      power *= 10;
   }

   //Print value
   cout << "Integer value = " << numInt << endl;
}

//Includes

#include <iostream>

using namespace std;

void main()

{

//Input number in string format

char numStr[] = "12345";

//Integer value of the number string

//to be calculated

int numInt = 0;

//Find string length. You can use a built in function

//but we are calculating the length manually.

int len = 0;

while (numStr[len] != '\\0') len++;

//This is needed to calculate powers of 10

int power = 1;

//Loop in the string character by character

//Get the current digit by subtracting the ASCII code of '0'

//from its ASCII code. You need to cast the rest to integer

//type. Then multiply the result by 10 raised to a power equal

//to the position of the character from right to left starting

//the count from 0. For example 2 in the example above has

//position 2

for (int i = len-1; i >= 0; i--)

{

numInt += (int)(numStr[i]-'0') * power;

power *= 10;

}

//Print value

cout << "Integer value = " << numInt << endl;

}

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String to integer c++

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