foo.c:1:1: warning: data definition has no type or storage class
 n1 = float(input("请输入第一个数"))
 ^~
foo.c:1:1: warning: type defaults to 'int' in declaration of 'n1' [-Wimplicit-int]
foo.c:1:6: error: expected expression before 'float'
 n1 = float(input("请输入第一个数"))
      ^~~~~

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