tolower.c

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

int main(int argc, char **argv)
{
    FILE *file;
    if(argc==3)
    {
        file = fopen(argv[2], "r");
    }
    char *line = malloc(sizeof(char)*1024);
    char **word = malloc(sizeof(char*)*1024);
    for(int i=0;i<1024;i++)
    {
        *(word+i) = malloc(sizeof(char)*1024);
    }
    int j=0;
    while(fgets(line, 1024, file)!=NULL)
    {
        line[strcspn(line,"\n")]='\0';
        int len = strlen(line);
        for(int i=0;i<len;i++)
        {
            if(line[i]>=65&&line[i]<=90)
            {
                line[i]+=32;
            }
        }
        strcpy(word[j++],line);
    }
    fclose(file);
    file = fopen(argv[2],"w+");
    for(int y=0;y<j;y++)
    {
        fprintf(file, "%s\n",word[y]);
    }
    fclose(file);
}