This is not a mixture of numbers and letters, that is "%lf". VA marks the "lf" as an error. "lf" is the letter "L" plus the letter "F". Generally, "lf" should not be an acceptable spelling, but "%lf" is used for double-precision for scanf() and scanf_s(). Similarly, "%f" is for float.
I'm using VS2019 version 16.1 Preview 3 and Build 2331 of VA, both are the latest versions. I don't think this issue only occurs in specific version. It should be general.
Moreover, it is very strange that VA won't show this error in the spell check dialog.
But it is certainly marked by VA.
You can use the following code for test:
#include <stdio.h>
#include <math.h>
int main(void) {
double a, b;
printf("Please input a nonnegative number:\n");
scanf_s("%lf", &a);
b = sqrt(a);
printf("Square root is %.3f\n", b);
return 0;
}
