As Gavin said, if you're a web dev, it'll be one of the first things you should learn. If web dev isn't your thing, you could easily get by not knowing it.
For Web development it is yes. You can't call yourself a Web designer if you don't know the Web trinity. https://www.sololearn.com/discuss/435653/?ref=app
Python — File Handling
Question is write a c program to print prime numbers up to n and print the largest number in array.
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Question - Java: Pyramid layers
Error in Program