Question

I was writing this code for a C program that transforms letters to lower case when called as:

./arg lower

and transforms them to upper case when invoked as:

./arg upper

Here is the code which I wrote, kindly help me out:

#include<stdio.h>
#include<ctype.h>
main(int argc,char *argv[])
{
    int i;
    char c;
    for(i=1;i<argc;++i)
    {

        if(*(argv+i)=="lower")
        {
             while((c=getchar())!=EOF)
                 {
                      c=tolower(c);
                      putchar(c);
                 }
        }
        if(*(argv+i)=="upper")
        {
            while((c=getchar())!=EOF)
                 {
                      c=toupper(c);
                      putchar(c);
                 }                    
        }
    }
    return 0;
}

Answer 1

You can’t do string comparisons like that in C, you need to use strcmp(3).

Better yet, use strncmp(3) and specify the size of your buffer.

Finally, for array access, you could use argv[i] instead of *(argv+i). The meaning is the same, but the first version is much more readable.

So, you’d want something like:

if (0 == strncmp(argv[i], "lower", 6)) {
    ...
}