String functions galore

In this post we will go over a bunch of string functions. I have added code comments to all of them so that you can follow them without much of an explanation.

Find the first occurrence of a character

// find the first occurrence of a character
int IndexOf(char *source, char searchChar)
{
    int currentPos = 0;
    
    // loop through the enite source
    while (*source)
    {
        // if the current character matches, return that position
        if (*source == searchChar)
            return currentPos;
        // no match. move to next position
        source++;
        currentPos++;
    }
        
    // no match was found
    return -1;
}

 

Check if two strings are equal

// check if two strings are equal
int IsEqual(char* s1, char* s2)
{
    // continue looping till either one string exists
    while (*s1 || *s2)
    {
        // if the chars do not match, return false
        if (*s1 != *s2)
            return 0;
            
        // chars are equal, move to next char
        s1++;
        s2++;
    }
    // we have a match, the strings are equal
    return 1;
}

 

Check if the first string is greater than the second

// check if the first string is greater than the second
int IsGreater(char *s1, char* s2)
{
    // loop through the entire first string
    while (*s1)
    {
        // if the characters do not match
        if (*s1 != *s2)
        {
            // if the char in first string is greater, 
            // return success
            if (*s1 > *s2)
                return 1;
            else
                return 0;
        }
        // the characters in both strings were same
        // move forward
        s1++;
        s2++;
    }
    // first string ended
    return 0;
}

 

Check if the first string is smaller than the second

// check if the first string is smaller than the second
int IsSmaller(char *s1, char* s2)
{
    // loop through the entire second string
    while (*s2)
    {
        // if the characters do not match
        if (*s1 != *s2)
        {
            // if the char in first string is lesser, 
            // return success
            if (*s1 < *s2)
                return 1;
            else
                return 0;
        }
        // the characters in both strings were same
        // move forward
        s1++;
        s2++;
    }
    // second string ended
    return 0;
}

 

Find the substring

// return the substring starting at position startPos
// and of length len
char* Substring(char* source, int startPos, int len)
{
    // move to the desired start position
    char *s = source + startPos;
    // initialize the return vale
    char *substr = new char[len + 1];

    int currentCount = 0;
    // loop for the desired length
    while (currentCount < len)
    {
        substr[currentCount] = *s;
        s++;
        currentCount++;
    }
    // terminate the return string
    substr[currentCount] = '\0';
        
    // return the substring
    return substr;
}

 

Extract leftmost n characters from the string

// extract leftmost n characters from the string
char* LeftSubstring(char* source, int len)
{
    // initialize the return value
    char *substr = new char[len + 1];

    int currentCount = 0;
    // loop for the desired length
    while (currentCount < len)
    {
        substr[currentCount] = *source;
        source++;
        currentCount++;
    }
    // terminate the return string
    substr[currentCount] = '\0';
        
    // return the substring
    return substr;
}

 

Extract rightmost n characters from the string

// extract rightmost n characters from the string
char* RightSubstring(char* source, int len)
{
    // initialize the return value
    char *substr = new char[len + 1];
    int strLen = strlen(source);

    // move to the desired position in the string
    char *s = source + (strLen - len);

    int currentCount = 0;
    // loop for the desired length
    while (currentCount < len)
    {
        substr[currentCount] = *s;
        s++;
        currentCount++;
    }
    // terminate the return string
    substr[currentCount] = '\0';
        
    // return the substring
    return substr;
}

 

Convert string to uppercase

// convert string to uppercase
void ToUpper(char *source)
{
    while (*source)
    {
        // if the char is upper in ASCII, make lower
        if (*source >= 97 && *source <= 123)
            *source -= 32;
        source++;
    }
}

 

Convert string to lowercase

// convert string to lowercase
void ToLower(char *source)
{
    while (*source)
    {
        // if the char is lower in ASCII, make upper
        if (*source >= 65 && *source <= 91)
            *source += 32;
        source++;
    }
}

 

Reverse a string

// reverse a string 
void Reverse(char *source)
{
    int strLen = strlen(source);
    char temp; // temp char for swapping
    // last char in the string
    char *revStr = source + (strLen - 1);
        
    int currPos = 0;
    // loop through half the string
    while (currPos < strLen / 2)
    {
        // swap the currPos char with 
        // the corresponding char position
        // from the end
        temp = *source;
        *source = *revStr;
        *revStr = temp;

        // increment/decrement the counters
        source++;
        revStr--;
        currPos++;
    }
}

 

Replace the first occurrence of a character with a new char

// Replace the first occurrence of a character with a new char 
int Replace(char *source, char oldChar, char newChar)
{
    // loop through the entire string
    while (*source)
    {
        // if we have a match?
        if (*source == oldChar)
        {
            // replace with new char
            *source = newChar;
            return 1;
        }
        // match not found, move to next position
        source++;
    }
    // no matches found
    return 0;
}