Compilare: main.c: In function 'find': main.c:9:15: warning: implicit declaration of function 'strstr' [-Wimplicit-function-declaration] char *p = strstr(s, tofind); ^~~~~~ main.c:9:15: warning: incompatible implicit declaration of built-in function 'strstr' main.c:9:15: note: include '<string.h>' or provide a declaration of 'strstr' main.c: In function 'main': main.c:39:14: warning: implicit declaration of function 'strlen' [-Wimplicit-function-declaration] int l1 = strlen(s1); ^~~~~~ main.c:39:14: warning: incompatible implicit declaration of built-in function 'strlen' main.c:39:14: note: include '<string.h>' or provide a declaration of 'strlen' main.c:38:5: warning: ignoring return value of 'fgets', declared with attribute warn_unused_result [-Wunused-result] fgets(s1, 1000, fin); ^~~~~~~~~~~~~~~~~~~~ main.c:40:5: warning: ignoring return value of 'fgets', declared with attribute warn_unused_result [-Wunused-result] fgets(s2, 1000, fin); ^~~~~~~~~~~~~~~~~~~~