Compilare: main.c:5:6: warning: return type of 'main' is not 'int' [-Wmain] void main() { ^~~~ main.c: In function 'main': main.c:13:16: warning: suggest parentheses around '&&' within '||' [-Wparentheses] if (c >= 'A' && c <= 'Z' || c >= 'a' && c <= 'z') { ~~~~~~~~~^~~~~~~~~~~ main.c:29:9: warning: 'return' with a value, in function returning void return 0; ^ main.c:5:6: note: declared here void main() { ^~~~