Question

1. We will write a simple program that simply uses the three standard library functions. The following is a high level description of the main program (main.cpp). In this program, please do the following:
   • Include the C-string library. #include <cstring>
   • Declare the following C-style string: char line[] = "ls -l -a | wc -c >> myfile";.
   • Declare a variable of type size_t named "len".
   • Use the builtin strlen function to compute the length of the variable "line". Store the result in "len".
   • Output the value of "len" ("The length of 'line' is..."). (The answer should be 26 for this string.)
   • Create an array of 10 C-strings named "strArray". (char* strArray[10];)
   • Initialize each element of "strArray" to be a string containing just the null character, "\0". Note that there is a difference between the null character, '\0', and a string containing only the null character, "\0". The former is a character, just like 'a' or '{'. The latter is a string that is functionally empty, e.g. "".
   • Use the builtin strtok function to split "line" into pieces using a space as the delimiter. Each piece will be placed into "strArray". Here is an overview of how that should work: 1) Declare an integer named "pieces" and set it to 0 initially. 2) Create a char* named "ptr" and assign it the return value of strtok, where "line" and " " are the two arguments. 3) Create a while loop that iterates while "ptr" is not NULL. 4) Set "strArray[pieces]" equal to "ptr". 5) Set "ptr" to the return value of strtok, where NULL and " " are the two arguments. 6) Increment "pieces".
   • Using "pieces" as the upper index, print out each element of "strArray", one per line. E.g. "strArray[0] = ...". Notice that we have split the original "line" variable into pieces. strArray[0] should be "ls", strArray[1] should be "-l", and so on.
   • Create a size_t variable named "size", and initialize it to 0.
   • Again using "pieces" as the upper index, calculate the sum of the lengths of each string in "strArray". Put the result in "size".
   • Create a size_t variable named "numBlanks". See if you can initialize it to the number of spaces in "line". HINT: You can do it using information you already have. You don't need another loop!
   • Print out the value of "numBlanks". (E.g. "The number of blanks is ..."). You can check for yourself that the answer should be 7 for the string we gave you.
   • Our last task will be to concatenate the elements of "strArray" into one big string using strcat. First, create a C-string that is large enough to hold the result. (char* result = new char[size + 1];)
   • Set result[0] to the null character, '\0'.
   • Once more, using "pieces" as the upper bound, call strcat successively with "result" as the first argument and strArray[i] as the second.
   • Print out the contents of "result" (e.g. "The concatenation of all strings in strArray is: ...").
   • Finally, clean up after yourself by entering "delete[] result;" Remember, for each new, there MUST BE a matching delete.

Answer 1

Solution:

#include<iostream>

#include<cstring>

using namespace std;

int main()

{

    //Declaring C style string

    char line[]="ls -l -a | wc -c >> myfile";

    size_t len;

    //Finding length of string 'line'

    len=strlen(line);

    //Printing the length of string

    cout<<"The length of 'line' is "<<len<<endl;

    //Declaring an array of C-strings

    char* strArray[10];

    int i=0;

    //Initializing each string to \0

    while(i<10)

    {

        strArray[i]=(char *)"\0";   

        i++;

    }

    int pieces;

    pieces=0;

    char* ptr;

    //breaking line into tokens based on delimiter " "

    ptr=strtok(line," ");

    while(ptr!=NULL)

    {

        strArray[pieces]=ptr;

        ptr=strtok(NULL," ");

        pieces=pieces+1;

    }

    //Printing contents of strArray

    for(i=0;i<pieces;i++)

        cout<<"strArray["<<i<<"] = "<<strArray[i]<<endl;

    //Finding sum of lengths of all strings in strArray

    size_t size=0;

    for(i=0;i<pieces;i++)

        size=size+strlen(strArray[i]);

    

    //Finding number of blanks in line

    size_t numBlanks=pieces-1;

    cout<<"The number of blanks is "<<numBlanks<<endl;

    char* result = new char[size+1];

    result[0]='\0';

    //Concatenating all strings in strArray into a big string

    for(i=0;i<pieces;i++)

        strcat(result,strArray[i]);

    

    //Printing the result

    cout<<"The concatenation of all strings in strArray is: "<<result;

    delete[] result;

    return 0;

}

Output: