how epoch vary in neural network meaning code example

Example 1: Epoch vs Batch Size vs Iterations

One Epoch is when an ENTIRE dataset is passed forward and backward 
through the neural network only ONCE.

Batch Size is the Total number of training examples present in a 
single batch.

Iterations is the number of batches needed to complete one epoch.

Example 2: epochs

One Epoch is completed when a complete dataset is cycled forward and backward through the neural network or you can say your neural network has watched the entire dataset for once.