Compilare: user.cpp: In function ‘int main()’: user.cpp:15:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=1;i<=n;i++) ^ user.cpp:16:24: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int j=1;j<=n; j++) {f>>a[i][j];sp[i][j]=12345678;} ^ user.cpp:17:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for( i=0;i<=n+1;i++) {a[0][i]=a[n+1][i]=a[i][0]=a[i][n+1]=-1;} ^