I'm trying to compile a source code from www.st.com/.../dm00050879.pdf in Keil. I get the following errors Error: L6218E: Undefined symbol ADC_GetConversionValue (referred from main.o). Error: L6218E: Undefined symbol ADC_GetFlagStatus (referred from main.o). Error: L6218E: Undefined symbol ADC_SoftwareStartConv (referred from main.o). I'm a beginner here, how to resolve them ?