Error(s):

source_file.c: In function ‘main’:
source_file.c:14:5: error: too few arguments to function ‘esmayor’
     printf("\n\nEl mayor es ... %lf\n\n", esmayor(x));
     ^
source_file.c:5:8: note: declared here
 double esmayor(double a, double b);
        ^
source_file.c:11:39: warning: ignoring return value of ‘scanf’, declared with attribute warn_unused_result [-Wunused-result]
     printf("\nValor de x ... "); scanf(" %lf", &x);
                                       ^
source_file.c:12:39: warning: ignoring return value of ‘scanf’, declared with attribute warn_unused_result [-Wunused-result]
     printf("\nValor de y ... "); scanf(" %lf", &y);
                                       ^