warning: type specifier missing, defaults to 'int' [-Wimplicit-int

We can either tell the compiler to use the C language standard C90 (ANSI), which was modern when the book was written. Do it by using parameter -std=c90 or -ansi to the compiler, like this:

$ cc -ansi t.c -o t.out

or you can rewrite the program to adhere to a newer standard (C99), which is what your compiler uses by default, by adding a return type to the main function, like this:

int main()
{
    ……

    return 0;
}

Give main a int return type. and make sure to add return 0; as the last statement.  It solves the problem.

note

• ANSI is American National Standards Institute. 
• t.out is an executable file. run

$ ./t.out

it will print expected result. If we do not want to type "./", then add "." to our PATH.

  

references

1. https://stackoverflow.com/questions/43819099/how-to-not-invoke-warning-type-specifier-missing