Character replacing in a string

suppose I have string like "this str1ng for test" now开发者_开发问答 i want to check if character at position [i-1] and [i+1] are both alphabet but character at [i] is number, like this example in word "str1ng" then character at position [i] replaced by appropriate alphabet. or vice versa.

I need this for post processing for output of OCR. TQ

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You might have an easier time using Regular Expressions.

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NSString are immutable, so you'll have to create a new NSMutableString from it, and mutate this copy, or to allocate a unichar* buffer, copy data from the NSString, perform the correction, and then recreate a new NSString from the result. Once you're working on a mutable copy of the string, you can use whatever algorithm you want.

So you'll need to have a function like that:

- (NSString*)correctOCRErrors:(NSString*)string
{
    BOOL hasError = NO;
    for (int i = 0; i < [string length]; ++ i)
    {
        if (isIncorrect([string characterAtIndex:i]))
        {
            hasError = YES;
            break;
        }
    }

    if (hasError)
    {
        unichar* buffer = (unichar*)malloc([string length]);
        for (int i = 0; i < [string length]; ++ i)
        {
            unichar chr = [string characterAtIndex:i];
            if (isIncorrect(chr))
                chr = correctChar(chr);
            buffer[i] = chr;
        }
        string = [[[NSString alloc] initWithCharactersNoCopy:buffer length:[string length] freeWhenDone:YES] autorelease];
    }

    return string;
}

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You can access character in a NSString by passing a message charAtIndex:(NSUInteger)index. And now you can get the ascii value at the particular index you are interested in and change it according to your requirement.

NSString Ref

Hope this is helpful !