Reading Compiler Output

Compile with warnings ON, always

gcc -std=c23 -Wall -Wextra -o app main.c

-Wall -Wextra is the default posture for this course's challenges too: the build warnings you see are the same ones the grader sees.

The warnings that mark real bugs

• unused variable — you computed something and never used it: often a forgotten step
• uninitialized — the value is read before any assignment: undefined behavior waiting to happen
• wrong format specifier — printf("%d", 3.14) prints garbage: the type and the format must agree
• control reaches end of non-void function — a code path returns nothing
• assignment in condition — if (x = 5) assigns, then tests 5; you probably meant ==

Read errors bottom-up

The FIRST error is the real one; later errors are often its shockwaves. Fix the first, recompile, repeat. And read the caret line (^) — the compiler points at the exact token it choked on.

Error vs warning

A warning compiles anyway — the program runs, wrongly. The discipline: treat every warning as a bug. -Werror (turn warnings into errors) is how professional builds enforce it.