Question

using c and pointers only

1. You will read in two strings from a file cp4in_1.txt at a time (there will be 2n strings, and you will read them until EOF) and then do the following. You alternately take characters from the two strings and string them together and create a new string which you will store in a new string variable. You may assume that each string is no more than 20 characters long (not including the null terminator), but can be far less. You must use pointers. You may store each string in an array, but are not allowed to treat the string as a character array in the sense that you may not have statements like c[i] = a[j], but rather *c = *a is allowed.
Example String1: ABCDE String2: PQRSw
Output: APBQCRDSEw
Example String1: ABCDE String2: P%R
Output: APB%CRDE
Example String1:
String2: PQR
Output: PQR

Answer 1

Note: Assume the size of a string in input file cannot be more than 20 character.

Screenshot of the code:

Sample Input File (cp4in_1.txt):

Sample Output:

Code to copy:

//Include required header files.

#include <stdio.h>

#include <string.h>

#include <stdlib.h>

//Start the execution of the main() method.

int main(void)

{

//Create a pointer variable of FILE type.

FILE* infile;

//Open the input file in read mode.

infile = fopen("cp4in_1.txt", "r");

//Allocate memory for two c-strings str1 and str2.

char* str1 = (char*)malloc(20 * sizeof(char));

char* str2 = (char*)malloc(20 * sizeof(char));

//Declare two integer variables to store the size of

//the strings str1 and str2.

int str1Size, str2Size;

//If the file pointer infile is null, then file does

//not exist.

if(infile == NULL)

{

    printf("File cannot be open successfully!\n");

    return 1;

}

//Traverse the file using a while loop till the line

//read from the file using fgets() is not null.

while(fgets(str1, 20, infile) != NULL)

{

    //Allocate memory for the third string str3.

    char* str3 = (char*)malloc(40 * sizeof(char));

   

    //Get the size of the string str1 using strlen().

    str1Size = strlen(str1);

    //If the last character in the string str1 is a new

    //line character, then replace it with null

    //character and decrement the size of the string

    //str1 by 1.

    if(str1[str1Size - 1] == '\n')

    {

      str1[str1Size - 1] = '\0';

      str1Size--;

    }

    //Read another line from the file.

    fgets(str2, 20, infile);

    //Get the size of the string str2 using strlen().

    str2Size = strlen(str2);

    //If the last character in the string str2 is a new

    //line character, then replace it with null

    //character and decrement the size of the string

    //str2 by 1.

    if(str2[str2Size - 1] == '\n')

    {

      str2[str2Size - 1] = '\0';

      str2Size--;

    }

  

    //Declare and initialize required integer

    //variables to store the index value of the strings

    //str1, str2, and str3.

    int index1, index2, index3;

    index1 = index2 = index3 = 0;

   

    //Start a while loop till the value of index1 and

    //index2 is less than the size of strings str1

    //and str2.

    while((index1 < str1Size) && (index2 < str2Size))

    {

      //Store the character of the string str1 at index1

      //to the string str3 at index3.

    *(str3 + index3) = *(str1 + index1);

      //Increment the value of the index3 by 1.

      index3++;

      //Store the character of the string str2 at index2

      //to the string str3 at index3.

      *(str3 + index3) = *(str2 + index2);

     

      //Increment the values of index1, index2, and

      //index3 by 1.

      index1++;

      index2++;

      index3++;

    }

    //Start a while loop till the value of index1 is

    //less than str1Size i.e. size of the string str1.

    while(index1 < str1Size)

    {

      //Store the character of the string str1 at

      //index1 to the string str3 at index3.

      *(str3 + index3) = *(str1 + index1);

      //Increment the values of index1 and index3 by 1.

      index1++;

      index3++;

    }

    //Start a while loop till the value of index2 is

    //less than str2Size i.e. size of the string str2.

    while(index2 < str2Size)

    {

      //Store the character of the string str2 at

      //index2 to the string str3 at index3.

      *(str3 + index3) = *(str2 + index2);

      //Increment the values of index2 and index3 by 1.

      index2++;

      index3++;

    }

    //Display the value of string str3 containing

    //alternate characters from both string str1 and

    //str2.

    printf("%s\n", str3);

}

//Close the file.

fclose(infile);

return 0;

}

Sample Input File (cp4in_1.txt):

ABCDE

PQRSTFG

acegikmoqsuwyz

bdfhjlnprtvx

ABCDE

PQRSw

ABCDE

P%R

PQR