warning: comparison between pointer and integer [enabled by default] in c

c, comparison, gcc, ubuntu

Solution

`NULL` is not the same as the null-terminator character. You should use `'\0'` instead.

Problem

I want to check whether the user input contains only digits or not. So, I use the following code: ``` for(i = 0; argv[1][i] != NULL; i++) if(!isdigit(argv[1][i])) { printf("Error"); return -1; } ``` It works well but I got this warning: ``` warning: comparison between pointer and integer [enabled by default] ``` since `argv[1][i]` is an Integer and `NULL` is a pointer. How can I avoid such warning?

Original source