String Interview Questions

QUESTION-21 Implement Regular Expression Matching

Answer-

#define MATCH printf("\nThe Text Matches The Regular Expression");
#define NOTMATCH printf("\nThe Text Doesn't match the Regular Expression");
 
char reg[20], text[20];
 
int main()
{
    int i, rlen, tlen, f = 0;
    char ans;
 
    do {
            printf("\nEnter the Regular Expression\n");    
            scanf(" %[^\n]s", reg);
            for (rlen = 0; reg[rlen] != '\0';rlen++);
            printf("\nEnter the text\n");
            scanf(" %[^\n]s", text);
            for (tlen = 0;text[tlen] != '\0' ; tlen++);
            if (reg[0] == '*')
            {
                printf("\nInvalid regular expression");
            }

            if ((reg[0] >= 65 && reg[0] <= 90) || (reg[0] >= 97 && reg[0] <=122))
            {
                if (reg[0] == text [0])
                {
                    switch (reg[1]) 
                    {
                    case '.' :
                        switch (reg[2])
                        {
                        case '*':
                            if (tlen != 1)
                            {
                                if (reg[3] == text[tlen-1])
                                {
                                    MATCH;
                                }
                                else
                                {
                                    NOTMATCH;
                                }
                            }
                            else
                            {
                                NOTMATCH;
                            }
                            break;
                        case '+':
                            if (text[1] != reg[3])
                            {
                                if (reg[3] == text[tlen - 1])
                                {
                                    MATCH;
                                }
                                else
                                {
                                    NOTMATCH;
                                }
                            }
                            break;
                        case '?':
                            if (text[1] == reg[3] || text[2] == reg[3])
                            {
                                if (text[1] == reg[3] || text[2] == reg[3])
                                {
                                    MATCH;
                                }
                                else
                                {
                                    NOTMATCH;
                                }
                            }
                            else
                            {
                                NOTMATCH;
                            }
                             break;
                            }
                            break;
                        case '*':
                            if (reg[rlen-1] == text[tlen-1])
                            {
                                for (i = 0;i <= tlen-2;i++)
                                {
                                    if(text[i] == reg[0])
                                    {
                                        f = 1;        
                                    }
                                    else 
                                    {
                                        f = 0;
                                    }
                                }
                                if ( f == 1)
                                {
                                    MATCH;
                                }
                                else
                                {
                                    NOTMATCH;
                                }
                            }
                            else
                            {
                                NOTMATCH;
                            }
                            break;
                    case '+' :
                        if (tlen <= 2)
                        {    
                            NOTMATCH;
                        }
                        else if (reg[rlen-1] == text[tlen-1])
                        {
                            for (i = 0;i < tlen-2;i++)
                            {
                                if (text[i] == reg[0])
                                {
                                    f = 1;
                                }
                                else
                                {
                                    f = 0;
                                }
                            }
 
                            if (f == 1)
                            {
                                MATCH;
                            }
                            else 
                            {
                                NOTMATCH;
                            }
                        }
                            break;
                    case '?':
                        if (reg[rlen -1] == text[tlen-1])
                        {
                            MATCH;
                        }
                        else
                        {
                            NOTMATCH;
                        }
                    break;
                } 
 
            }
            else
                printf("Does not match");             
        }
 
        else if (reg[0] == '^')
        {
            if (reg[1] == text[0])
            {
                MATCH;
            }
            else
            {
                NOTMATCH;
            }
        }
 
        else if (reg[rlen-1] == '$')
        {
            if (reg[rlen-2] == text[rlen-1])
            {
                MATCH;
            }
            else
            { 
                NOTMATCH;
            }
        }
 
        else
            printf("Not Implemented");
        printf("\nDo you want to continue?(Y/N)");
        scanf(" %c", &ans);
    } 
while (ans == 'Y' || ans == 'y');
}
 

QUESTION-22 Implement strpbrk() Function

Answer-

 
char* strpbrk(char *, char *);
 
int main()
{
    char string1[50], string2[50];
    char *pos;
 
    printf("Enter the String:\n");
    scanf(" %[^\n]s", string1);
    printf("\nEnter the Character Set:\n");
    scanf(" %[^\n]s", string2);
    pos=strpbrk(string1, string2);
    printf("%s", pos);
}
 
 
char* strpbrk(char *string1, char *string2)
{
    int i, j, pos, flag = 0;
    for (i = 0; string1[i] != '\0';i++);
    pos = i;
    for (i = 0;string2[i] != '\0';i++)
    {
        for (j = 0;string1[j] != '\0';j++)
        {
            if (string2[i] == string1[j])
            {
                if ( j <= p1)
                {
                    pos = j;    
                    flag = 1;    
                }
            }
         }        
    }
    if (flag == 1)
    {
        return &string1[pos];
    }
    else
    {
        return NULL;
    }
}

QUESTION-23 Sort String Ignoring Whitespaces and Repeating Characters Only Once

Answer-

#define SIZE 50
 
void main()
{
    char string[SIZE], string1[SIZE], string2[SIZE];
    int i, j = 0, a = 0, temp, len = 0, len1 = 0, k = 0;
 
    printf("\nEnter a string:");
    scanf("%[^\n]s", string1);
 
    for (i = 0;string1[i] != '\0';i++)
    {    
        if (string1[i] == ' ')
        {
            continue;
        }
        string[j++] = string1[i];
    }
    for (i = 0;string[i] != '\0';i++)
    {
        for (j = i + 1;string[j] != '\0';j++)
        {
            if (string[i] > string[j])
            {
                temp = string[i];
                string[i] = string[j];
                string[j] = temp;
            }
        }
    }
    string[i] = '\0';
    len = strlen(string);
 
    for (i = 0;string[i] != '\0';i++)
    {
        if (string[i] == string[i + 1] && string[i + 1] != '\0')
        {
            k++;
            continue;
        }
        string2[a++] = string[i];
        string[a] = '\0';
    }
    len1 = len - k;
    printf("The sorted string is:");
    for (temp = 0;temp < len1;temp++)
    {
        printf("%c", string2[temp]);
    }
}