用C实现数字电压电流表：1、由外部输入直流电压电流，电压范围20V，电流范围1A；
2、电压/电流通过开关切换；
3、显示：数码管显示电压值/电流值，精度0.01。
-Implementation using digital voltage ammeter C: 1, by the external input DC voltage and current, voltage range of 20V, the current scope of 1A 2, voltage/current through the switch 3, Display: Digital display voltage/current value, the accuracy of 0.01.
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