Compilare: user.c: In function ‘main’: user.c:16:5: warning: implicit declaration of function ‘strlen’ [-Wimplicit-function-declaration] for(i = 0; i < strlen(a); i++) { ^ user.c:16:20: warning: incompatible implicit declaration of built-in function ‘strlen’ [enabled by default] for(i = 0; i < strlen(a); i++) { ^ user.c:9:32: warning: unused variable ‘x’ [-Wunused-variable] char a[100001], b[100001], x; ^ user.c:12:11: warning: ignoring return value of ‘fscanf’, declared with attribute warn_unused_result [-Wunused-result] fscanf(in, "%s", a); ^ user.c:13:11: warning: ignoring return value of ‘fscanf’, declared with attribute warn_unused_result [-Wunused-result] fscanf(in, "%s", b); ^