Why am I getting “undefined reference to sqrt” error even though I inclu de math.h header?

The math library must be linked in when building the executable. How to do this varies by environment, but in Linux/Unix, just add -lm to the command:

gcc test.c -o test -lm

The math library is named libm.so, and the -l command option assumes a lib prefix and .a or .so suffix

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