How to implement the calculation of an expression with logarithmic functions?

Question

C++ / C#

Please advise how to accomplish this task. I'm new to programming and don't know where to start. A string is entered from the console, which is a mathematical expression with logarithmic functions (ln, lg, log). It is necessary to analyze the string and count the number of logarithms used in the expression, calculate their value, and display a string with logarithm values ​​substituted for it. Tell me how to implement this, I want to use C / C ++. Thanks in advance for any help.