Converting Mixed Character C String to Lower Case

Question

I am running into a wall here because I don't see how I can iterate over the string and use the tolower() function without severely breaking my dynamically allocating array. Any advice would be suggested.

while (fscanf(file, "%s", str) != EOF) { 
    //doubles the word_alloc/str_array if we have more words than allocated
    if(ThreadData.word_count >= ThreadData.word_alloc) {
        ThreadData.word_alloc *= 2;
        ThreadData.str_array =(char **) realloc(ThreadData.str_array, sizeof(char*) * ThreadData.word_alloc);
    }       
    ThreadData.str_array[ThreadData.word_count] = (char *) malloc(sizeof(char) * (strlen(str) + 1));
    strcpy(ThreadData.str_array[ThreadData.word_count], str);
    ++ThreadData.word_count;
}

Answer 1

It is helpful to have a utility function to lowercase/uppercase/titlecase/whatever you want to do to your string, such as:

#include <ctype.h>

char * lowercase( char * s )
{
  for (char * p = s;  *p;  ++p)
  {
    *p = tolower( *p );
  }
  return s;
}

Now, since your data is an array of strings , just use the function on each string in your data. With the function defined as it is above, you can do it in-line with your copy:

ThreadData.str_array[ThreadData.word_count] = (char *) malloc(sizeof(char) * (strlen(str) + 1));
lowercase(strcpy(ThreadData.str_array[ThreadData.word_count], str));
++ThreadData.word_count;

Remember to keep a good reference handy:

• https://en.cppreference.com/w/c
  A very good one, but very technical. Takes some time to get used to reading it.

• https://cplusplus.com/reference/
  Gets pooh-poohed all the time, but isn't all that bad. Very much easier for the beginner to follow.

Answer 2

alternative without using tolower library

If you want to convert a word from upper case to lower case, you can use the ASCII table.

Here my program to convert it !

main.h

#ifndef _HEADER_H_
#define _HEADER_H_

void fill_str(char*);
void convert_to_lower_case(char*);

#endif

main.c

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

int main(){
    int size = 15; // Size of your string
    char* str = (char*) malloc(sizeof(char) * size);
    fill_str(str);
    convert_to_lower_case(str);
    printf("%s", str);
    return 0;
}

void fill_str(char* str){
    printf("Enter your word : ");
    scanf("%s", str);
}

void convert_to_lower_case(char* str){
    int i = 0;
    while(str[i] != '\0'){
        if( (int)str[i] >= 65 && (int)str[i] <= 90){ // We are verifying if the ascii code of a character is in upper case
            int ascii = str[i] + 32; // Example: ASCII code of "A" => 65 and "a" => 97. So 97 - 65 = 32;
            str[i] = (char) ascii;
        }
        i++;
    }
}