cezar.c: In function 'main': cezar.c:15: warning: implicit declaration of function 'strlen' cezar.c:15: warning: incompatible implicit declaration of built-in function 'strlen' cezar.c:12: warning: ignoring return value of 'fgets', declared with attribute warn_unused_result cezar.c:14: warning: ignoring return value of 'fscanf', declared with attribute warn_unused_result