$$100-98+96-94+92-90+\ldots +8-6+4-2+0=$$． 
Overseas Competition->Knowledge Point->Calculation Modules->Whole Numbers->Whole Numbers Addition and Subtraction 
$$\left( 100-98 \right)+\left( 96-94 \right)+\ldots +\left( 8-6 \right)+\left( 4-2 \right)+0=2\times 25+0=50$$. 