I am trying to write a script in c that generates a string of alphanumerical values,based on the desired size of the user input, and then it sorts it.

#include <stdio.h>
#include <stdlib.h>

#define FIRST_CHAR 'a'
#define LAST_CHAR 'z'
#define NULL_CHAR '\0'


char *randomString( int minSize, int maxSize){
int i,strSize;
char *newStr;
    strSize = minSize   ( rand() % (maxSize-minSize   1 ) );
    newStr = (char*)malloc(strSize   1 );
    if (newStr == NULL) {
        printf( " \n Error in memory allocation. Cannot create random string. \n " );
        return NULL;
    }
    for (i = 0; i < strSize; i  ) {
        newStr[i] = FIRST_CHAR   (rand() % (LAST_CHAR - FIRST_CHAR   1));
    }
    newStr[i] = NULL_CHAR;
return newStr;
}

void printStrings(char **strArray, int strArraySize)
{
    int i;
    for(i=0;i<strArraySize;  i)
    {
        printf("%s",strArray[i]);
    }
    printf("/n");
}
char *sort(char **strArray, int strArraySize)
{int i,j;
 char *sortedArray;
    for(i=0;i<strArraySize;  i)
    {
        for(j=FIRST_CHAR;j<=LAST_CHAR;  i)
        {
            if(strArray[i]==j)
            {
                strArray[i]=sortedArray[i];
            }
        }
    }
    sortedArray[i]= NULL_CHAR;
return sortedArray;
}

int main()
{int size,minSize=5,maxSize=20;
 char** str;
    printf("Dwse plithos alpharithmitikon\n");
    scanf("%d",&size);
    **str=*randomString(minSize,maxSize);

    printf("Seira pou dimiourgithike.\n");
    printStrings(str,size);

    printf("Seira pou taksinomithike.\n");
    printStrings(sort(str,size),size);

    return 0;
}

the main issue is that i cant wrap my head around the proper use of pointers in c. I am aware that it is of important use,especially while working with alphanumerical strings, but i am just not there yet. Thanks in advance !

CodePudding user response：

Here is an example of a program that generates a string of alphanumeric characters then sorts it:

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <string.h>

#define LENGTH 10

// Generate a random alphanumeric string
char* gen_str() {
  char* str = malloc(LENGTH   1);
  static const char alphanum[] = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";

  for (int i = 0; i < LENGTH; i  ) {
    str[i] = alphanum[rand() % (sizeof(alphanum) - 1)];
  }
  str[LENGTH] = 0;
  return str;
}

// Compare two strings for sorting
int str_cmp(const void* a, const void* b) {
  const char* str1 = *(const char**) a;
  const char* str2 = *(const char**) b;

  return strcmp(str1, str2);
}

int main() {
  srand(time(0));

  // Generate an array of random alphanumeric strings
  char** str_arr = malloc(LENGTH * sizeof(char*));
  for (int i = 0; i < LENGTH; i  ) {
    str_arr[i] = gen_str();
  }

  // Print the unsorted array
  printf("Unsorted:\n");
  for (int i = 0; i < LENGTH; i  ) {
    printf("%s\n", str_arr[i]);
  }

  // Sort the array using qsort
  qsort(str_arr, LENGTH, sizeof(char*), str_cmp);

  // Print the sorted array
  printf("\nSorted:\n");
  for (int i = 0; i < LENGTH; i  ) {
    printf("%s\n", str_arr[i]);
  }

  return 0;
}

This program uses the rand() function to generate random numbers, the malloc() function to dynamically allocate memory, and the qsort() function to sort the array of strings.

CodePudding user response：

While the following generator is not truly random (what is?), it delivers a random number of random length ASCII "strings" (actually, just one string sprinkled with LF characters) created in sorted order. If nothing else, it provides a starting point from which to refine a better solution.

char palette[] = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";

int main( void ) {
    srand( time( 0 ) );

    // some constants
    const int obufsz = 512;
    const int maxStrLen = 15;

    // the output buffer
    char obuf[ obufsz ], *op = obuf;

    // random number of strings (min: 5, max 20) 
    int nStrs = 5   rand()%(obufsz/maxStrLen);
    if( nStrs > 20 ) nStrs = 20;

    // increment so that successive first chars are always larger
    int incr = sizeof palette / nStrs;

    for( int strNo = 0; strNo < nStrs; strNo   ) {
        // assign the 'ascending' first char
        *op   = palette[ strNo * incr   (rand() % incr) ];

        // assign more chars (variable length)
        for( int charNo = 1   rand()%(maxStrLen-2); charNo; charNo-- )
            *op   = palette[ rand() % (sizeof palette - 1 ) ];

        // a LF for eventual printing
        *op   = '\n';
    }
    *op   = '\0';

    puts( obuf );

    return 0;
}

If you want to wrap your head around using C's pointers, grab a pencil and paper and start drawing boxes and arrows. A box would be a memory location (a pointer variable) that contains the address of another box that is (often) the first element of a contiguous array of boxes each holding either a 'primitive' datatype (ie: a 'char' or an 'int', etc.), or holding a pointer to another memory location (ie: a pointer to a pointer.) "Boxes and arrows" - that's how most people come-to-terms with C's pointers.