Need help debugging: pset2 caesar

Question

Hi I tried running the following code -- although it is compiling it is not returning anything.

#include<cs50.h>
#include<stdio.h>
#include<ctype.h>
#include<stdlib.h>
#include<string.h>

int main(int argc, string argv[])
{
    while(argc != 2)
    {
        printf("Please provide 2 arguments.\n");
        return 1;
    }
    string a = GetString();
    int p = atoi(argv[1]);
    for(int i = 0; i < strlen(a); i++)
    {
        char m[i];
        if(('A' <= a[i] && a[i] <= 'Z') || ('a' <= a[i] && a[i] <= 'z'))
        {
            m[i] = (a[i] + p) % 26;
        }
        else
        {
            m[i] = a[i];
        }
    printf("%c", m[i]);
    }
return 0;
}

Answer 1

Problem lies within the if condition. decimal value of m[i] as per ascii will never exceeds 25 whereas the alphabets are starting from 65 and 97.