Inquiry about compiler warning(compiling C program)

Question

This is the code I'm compiling:

#include <stdio.h>
main(){
    printf("Table of temperature conversions\n");
    float fahr, celsius;
    int lower, upper, step;

    lower = 0;
    upper = 300;
    step = 10;

    celsius = lower;
    while(celsius <= upper){
        fahr = (9.0/5.0)*(celsius + 32.0);
        printf("%3.0f %6.1f\n", celsius, fahr);
        celsius = celsius + step;
    }
}

And I get the following warning:

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

I was just curious, what variable is it complaining about not having a typing?

Answer 1

The prototype for main should be:

int main(void) {
    // ...
    return 0;
}

If it is to take the command-line arguments:

int main(int argc, char** argv) {
    // ...
    return 0;
}

The return type (int) is required.

Answer 2

It is not complaining about a variable, but about the main function.

You should type int main() to suppress that warning.