%make cc -MD -Wall -O0 -fprofile-arcs -ftest-coverage -g -c enigma3.c enigma3.c: In function 'main': enigma3.c:111: warning: unused variable 'notch1Idx' enigma3.c:110: warning: unused variable 'rDiff' enigma3.c:107: warning: unused variable 'bytesRd' cc -Wall -O0 -fprofile-arcs -ftest-coverage -g -o enigma3 enigma3.o %./enigma3 Will run simple demo Input = ENIGMA REVEALED Output = QMJIDO MZWZJFJR %gcov enigma3.c File 'enigma3.c' Lines executed:73.47% of 98 enigma3.c:creating 'enigma3.c.gcov'