Getting error "Expression: string subscript out of range"

Question

I don't understand the problem here. I've researched it, it compiles fine but when I run the program it gives me the "Debug Assertion Failed!" error and the above explanation.

#include <iostream>
#include <string>
using namespace std;


bool checkVowel(char ch)
{
 switch(ch)
 {
     case 'a':
     case 'A':
     case 'e':
     case 'E':
     case 'i':
     case 'I':
     case 'o':
     case 'O':
     case 'u':
     case 'U':
          return true;
     default:
          return false;
 }}
int main()
{
string str;
char ch;
cout<<"Please enter a string, all vowels will be removed: ";
cin >> str;

for (int i=0;i=str.length();i++)
{

 if (checkVowel(str[i]))
     {
        str=str.erase(i);
 }}

cout << str;
}

Be very careful if you modify an object while you are traversing it. Be aware that your loop skips a character for each one it erases -- it moves on to the next position, skipping the character that 'slid' into the current due to the 'erase' operation. (This is a poor candidate for an if loop. Use while and don't increment i if you call erase.) — David Schwartz
– David Schwartz, Commented Nov 14, 2011 at 6:09

Mysticial · Accepted Answer · 2011-11-14 06:24:16Z

4

One error is here:

i=str.length()

should be:

i < str.length()

In your initial code, i=str.length() will always return true when the string is not-empty. So the effect is that you will be overrunning the string.

Furthermore, you don't want to increment the index when you do find a vowel, or you will skip the next character:

for (int i = 0; i < str.length(); )
{
    if (checkVowel(str[i]))
    {
        str.erase(i,1);
    }else{
        i++;
    }
}

Last thing: str=str.erase(i); is not necessary, just str.erase(i,1); is enough. (You'll need the second parameter as 1 as pointed out in the comments.)

edited Nov 14, 2011 at 6:24

answered Nov 14, 2011 at 6:00

Mysticial

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1 Comment

Blastfurnace Over a year ago

If you give string::erase a single numeric parameter it will erase to the end of the string. He should use str.erase(i,1);

Avinash · Accepted Answer · 2011-11-14 06:09:58Z

1

for condition is wrong , it should be for (int i=0;i <= str.length();i++)

Alternatively you can use STL remove_if

remove_if(str.begin(), str.end(), checkVowel);

Complete program will be.

#include <iostream>
#include <string>
#include <algorithm>
using namespace std;
bool checkVowel(char ch){
    switch(ch){
        case 'a':
        case 'A':
        case 'e':
        case 'E':
        case 'i':
        case 'I':
        case 'o':
        case 'O':
        case 'u':
        case 'U':
            return true;
        default:
            return false;
    }
}
int main(){
    string str;
    char ch;
    cout << "Please enter a string, all vowels will be removed: ";
    cin >> str;
    remove_if(str.begin(), str.end(), checkVowel);
    cout << str;
}

edited Nov 14, 2011 at 6:09

answered Nov 14, 2011 at 6:03

Avinash

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