calculator.c: In function 'multiply':
calculator.c:123: error: 'first' redeclared as different kind of symbol
calculator.c:119: error: previous definition of 'first' was here
calculator.c:123: error: 'second' redeclared as different kind of symbol
calculator.c:119: error: previous definition of 'second' was here
calculator.c: In function 'add':
calculator.c:134: error: 'first' redeclared as different kind of symbol
calculator.c:130: error: previous definition of 'first' was here
calculator.c:134: error: 'second' redeclared as different kind of symbol
calculator.c:130: error: previous definition of 'second' was here
calculator.c: In function 'divide':
calculator.c:144: error: 'first' redeclared as different kind of symbol
calculator.c:140: error: previous definition of 'first' was here
calculator.c:144: error: 'second' redeclared as different kind of symbol
calculator.c:140: error: previous definition of 'second' was here
calculator.c: In function 'subtract':
calculator.c:155: error: 'first' redeclared as different kind of symbol
calculator.c:151: error: previous definition of 'first' was here
calculator.c:155: error: 'second' redeclared as different kind of symbol
calculator.c:151: error: previous definition of 'second' was here
gcc: -E or -x required when input is from standard input