String manipulation can be fun

String manipulations are a favorite topic for interview questions. They are small, easy to whiteboard and test your thinking power and logic. They are a great source for SDET interviews and allow the interviewer to dig deeper into test case generation also.

So, let's start by going over some simple string operations. I chose to use C/C++ programming language for this section as pointer understanding is critical (even if you code in the managed world of C# and JAVA). Without further ado, let's review 3 simple string functions – length, copy and concatenation.

Find the length of the string

// Simple funtion to calculate the length of a string
// Basically, keep counting the chars till the end
// of the string (aka NULL pointer) is met
int StringLength(char *input)
{
    // initialize
    int length = 0;

    // loop through the entire string
    while (*input)
    {
        // increment the length
        length++;
        // move to next char
        // since *input points to the data
        // input contains the actual address
        // this is an example of pointer arithmetic
        input++;
    }
    return length;
}

String copy – copy source string over target

// string copy - copy source string over target string
// can you find a possible bug in the code?
void StringCopy(char* target, char *source)
{
    // loop through the source string
    // and replace the characters in the target string
    while (*source)
    {
        // assign the character
        *target = *source;
        // move the pointers to the next location
        target++;
        source++;
    }
    // terminate the target string
    *target = '\0';
}

String concatenate - concatenate 2 strings

// string concatenate - concatenate 2 strings
void StringConcatenate(char* target, char *source)
{
    // loop through the target string
    // till you find the end
    while (*target)
        target++;

    // now copy source characters to the target
    while (*source)
    {
        // assign the character
        *target = *source;
        // move the pointers to the next location
        target++;
        source++;
    }
    // terminate the target string
    *target = '\0';
}

All the above functions are self-explanatory. There are a few bugs and optimizations that can be done to these functions. I would like to leave that as an exercise for the readers and encourage you to post your responses.

In the next section, we will dig a little bit more deeper into strings.