Question

I want to reduce space between label and QLineEdit (QLabel is above QLineEdit). How can I achieve it? In the code I’m creating items, that I later put in some layouts.

QLabel* lgamma = new QLabel("Gamma");
gamma = new QLineEdit();
QLabel* lmin_linie = new QLabel(QString::fromUtf8("Min. il. zmian linii"));
min_lin = new QLineEdit();
// ...
QLabel* lmax_kursy = new QLabel(QString::fromUtf8("Max zm. il. kursów"));
max_kursy = new QLineEdit();
QGridLayout *lay = new QGridLayout(this);
QVBoxLayout *box1 = new QVBoxLayout();
QVBoxLayout *box2 = new QVBoxLayout();
// ...
QVBoxLayout *box12 = new QVBoxLayout();
box1->addWidget(lmin_linie);
box1->addWidget(min_lin);
box2->addWidget(lmax_lin);
box2->addWidget(max_lin);
// ...
box12->addWidget(literacje);
box12->addWidget(iteracje);
verticalColumn1->addLayout(box1);
verticalColumn1->addLayout(box2);
// ...
verticalColumn3->addLayout(box12);

start = new QPushButton("Start", this);
QHBoxLayout *corn = new QHBoxLayout();
corn->addLayout(verticalColumn1);
corn->addLayout(verticalColumn2);
corn->addLayout(verticalColumn3);
QVBoxLayout *rup = new QVBoxLayout();
rup->addLayout(corn);
rup->addWidget(start);

Answer 1

You can simply add a spacer to your layout.

QSpacerItem *spacer = new QSpacerItem(1, 50, QSizePolicy::Ignored, QSizePolicy::Expanding);
box1.addItem(spacer); 

Adapt the args or QSpacerItem for your needs, for examle QSizePolicy::Preferred could be better than QSizePolicy::Expanding, and reduce the preferred height (second argument).
Why don’t you use the easy way to do that GUI with Qt designer ?