Compilare: user.c: In function ‘mul’: user.c:7:7: warning: implicit declaration of function ‘memset’ [-Wimplicit-function-declaration] memset(C, 0, sizeof(C)); ^ user.c:7:7: warning: incompatible implicit declaration of built-in function ‘memset’ [enabled by default] user.c:14:7: warning: implicit declaration of function ‘memcpy’ [-Wimplicit-function-declaration] memcpy(A, C, sizeof(C)); ^ user.c:14:7: warning: incompatible implicit declaration of built-in function ‘memcpy’ [enabled by default] user.c: In function ‘main’: user.c:57:9: warning: incompatible implicit declaration of built-in function ‘memset’ [enabled by default] memset(b, 0, sizeof(b)); ^ user.c:67:9: warning: incompatible implicit declaration of built-in function ‘memcpy’ [enabled by default] memcpy(c, b, sizeof(c)); ^ user.c:53:11: warning: ignoring return value of ‘fscanf’, declared with attribute warn_unused_result [-Wunused-result] fscanf(f,"%d",&t); ^ user.c:56:15: warning: ignoring return value of ‘fscanf’, declared with attribute warn_unused_result [-Wunused-result] fscanf(f,"%lld",&n); ^