Getting the exit code of a shell script, in a C program
After you have closed a stream, you cannot perform any additional operations on it.
You should not call read or write or even pclose after you called pclose on a file object!
pclose means you are done with the FILE * and it will free all underlying data structures (proof).
Calling it the second time can yield anything, including 0.
Your code should look like this:
...int r = pclose(shell);if(WEXITSTATUS(r)==3){ printf("AAA\n");}else if(WEXITSTATUS(r)==4){ printf("BBB\n");} else { printf("Unexpected exit status %d\n", WEXITSTATUS(r));}...