Runtime error with space character removing function

[yodaliketaco]

This function is causing the program to crash, but I can't spot my error.

string removeSpaces (string input)
{
	string output;
	int n;
	int o = 0;
	for ( n = 0; n < (int)input.length(); n++ )
	{
		if (input[n] != ' ')
		{
			output[o] = input[n];
			o++;
		}
	}
	return output;
}

Any ideas for what is wrong with the function?

[.::SCHiM::.]

This function is causing the program to crash, but I can't spot my error.

string removeSpaces (string input)
{
	string output;
	int n;
	int o = 0;
	for ( n = 0; n < (int)input.length(); n++ )
	{
		if (input[n] != ' ')
		{
			output[o] = input[n];
			o++;
		}
	}
	return output;
}

Any ideas for what is wrong with the function?

There are a few things which could be causing this, first you can't use strings like this:

output[o] = input[n];

Use the member string::at, like this:

if(foo.at(bar) == 'foobar'){

foo.at(bar) = foobar.at(bar);

}

And why are you manually checking for spaces? The string class has a member (find) who searches and returns the position of a character or string inside the string.

if( foo.find(' ') != std::string::npos ){   // if it's found

foo.at( foo.find(' ') ) = '_';    // replace a space with an underscore

}

[mmbob]

There are a few things which could be causing this, first you can't use strings like this:

output[o] = input[n];

Use the member string::at, like this:

if(foo.at(bar) == 'foobar'){

foo.at(bar) = foobar.at(bar);

}

Using string[x] is the exact same as using string.at(x).

And why are you manually checking for spaces? The string class has a member (find) who searches and returns the position of a character or string inside the string.

if( foo.find(' ') != std::string::npos ){   // if it's found

foo.at( foo.find(' ') ) = '_';    // replace a space with an underscore

}

You can't easily remove characters from within the string, so he loops through the original string to copy the non-space characters over to the new string.

@yodaliketaco
The problem is probably that the output string has a length of 0, but you're trying to change characters past 0. A solution would be

if (input[n] != ' ')
{
	output.append(input[n]); // adds a character to the end of output
}

[yodaliketaco]

string::append removes the runtime error:

string removeSpaces (string input)
{
	string output;
	int n;
	int o = 0;
	for ( n = 0; n < (int)input.length(); n++ )
	{
		if (input[n] != ' ')
		{
			output.append(input, o, 1);
			o++;
		}
	}
	return output;
}

But the primary function isn't fulfilling its purpose. I must have a logic error: (Yes I know stringstream solves most of this; I prefer to write my own functions, that way I'm better prepared when there isn't a class for what I want to do.)

Here is the code:

//getNum returns integer value in base (base) of string input
int getNum (string input, int base)
{
	input = removeSpaces(input);
	int n;
	int i = 0;
	int total = 0;
	int mult;
	for ( n = 0; n < (int)input.length(); n++ )
	{
		if (numericChar(input[n], base) != NULL)
		{
			mult = numOfIntegers(input, base) - 1;
			mult = mult - i;
			mult = power((double)base, (double)mult);
			mult = (mult * numericChar(input[n], base));
			total = mult + total;
			i++;
		}
	}
	return total;
}
//power returns base^exponent as integer
double power (double base, double exponent)
{
	if (exponent > (double)1) return base * (power(base, (exponent - 1)));
	else if (exponent == (double)1) return base;
	else if (exponent == (double)0) return (double)1;
	else if (exponent < (double)0) return ( (double)1 / power(base, ((double)0 - exponent)));
	return NULL;
}
//numOfIntegers returns number of integers in string input as integer
int numOfIntegers (string input, int base)
{
	int n;
	int total = 0;
	for (n = 0; n < (int)input.length(); n++)
	{
		if (numericChar(input[n], base) != NULL) total++;
	}
	return total;
}
//removeSpaces returns string without spaces
string removeSpaces (string input)
{
	string output;
	int n;
	int o = 0;
	for ( n = 0; n < (int)input.length(); n++ )
	{
		if (input[n] != ' ')
		{
			output.append(input, o, 1);
			o++;
		}
	}
	return output;
}
//returns value of character up to base 16
int numericChar (char input, int base)
{
	if (input == '0') return 0;
	else if (input == '1') return 1;
	if (base > 2)
	{
		if (input == '2') return 2;
		if (base > 3)
		{
			if (input == '3') return 3;
			if (base > 4)
			{
				if (input == '4') return 4;
				if (base > 5)
				{
					if (input == '5') return 5;
					if (base > 6)
					{
						if (input == '6') return 6;
						if (base > 7)
						{
							if (input == '7') return 7;
							if (base > 8)
							{
								if (input == '8') return 8;
								if (base > 9)
								{
									if (input == '9') return 9;
									if (base > 10)
									{
										if (input == 'A' || input == 'a') return 10;
										if (base > 11)
										{
											if (input == 'B' || input == 'b') return 11;
											if (base > 12)
											{
												if (input == 'C' || input == 'c') return 12;
												if (base > 13)
												{
													if (input == 'D' || input == 'd') return 13;
													if (base > 14)
													{
														if (input == 'E' || input == 'e') return 14;
														if (base > 15)
														{
															if (input == 'F' || input == 'f') return 15;
														}
													}
												}
											}
										}
									}
								}
							}
						}
					}
				}
			}
		}
	}
	return NULL;
}

When spaces exist, it truncates the end of the string by a variable amount of characters. (Most of the time, either 1 or 2).
The point of removing the spaces was that they were acting as delimiters, with the function only returning numeric characters before the first space.

[258456]

wouldn't it be easier to do this with char* var; instead of a string type?