According to your example,  we can have a reaction as follows:  A + B to form C, D, and etc...  Herein, C is main product, D and other products are byproducts.

In my opinion, this problem can be calculated due to product.

Suppose in this reaction, B is so excess than A. Therefore, the amount of C is calculated based on A. Theoretically, the amount of C is 100 (g or mole) according to A, but in fact only 66 (g or mole). That means the yield is 66%.

Conversion is 100% that means no byproducts is created after reaction. The components in products only include C, A and B remains

According to your example,  we can have a reaction as follows:  A + B to form C, D, and etc...  Herein, C is main product, D and other products are byproducts.

In my opinion, this problem can be calculated due to product.

Suppose in this reaction, B is so excess than A. Therefore, the amount of C is calculated based on A. Theoretically, the amount of C is 100 (g or mole) according to A, but in fact only 66 (g or mole). That means the yield is 66%.

Conversion is 100% that means no byproducts is created after reaction. The components in products only include C, A and B remains

Conversion means how much of the reactants are consumed or converted into products, and yield means the amount of a specific product produced during a reaction. 

I agree with wagas Ahmad. in addition to that , reaction yield is a measure of the efficiency of the reactant to reactant conversion to the desired product

conversion is the amount of reactant converted into products without forming byproducts means excluding the byproduct, where as yield is amount of product obtained from amount of reactant used. yield is ratio of theorotical yield to practical yield.

Making it simple:

Conversion: how much reactants have converted/consumed?

Yield: how much a desired products were produced/formed?

Conversion means converting amount of reactant to products.

Selectivity; converting to the specific product.

Yield= conversion *selectivity

Yield means the amount of converting the reactant to the specific product

The conversion rate is the fraction of a reagent that reacts in a chemical reaction.

x =(n0-nt)/n0

The yield refers to the ratio between the amount of product obtained and the maximum amount that would be obtained if the reaction was complete.

Thanks Youcef ....