c++ – …redeclared as different kind of symbol?

You are redefinign low and high inside the function which clash with those defined in the parameters.

The for loop is doing

for(x=low;x<=high;x++)
{
   delta_x = x+delta_x;
}

did you mean it to do

for(x=low;x<=high;x++)
{
   delta_x = x+delta_x;
   ans = delta_x*s;
}

However I think you wanted to do ans += delta_x*s;

lowand high are already passed as parameters of your integrateF method. But they are redeclared again inside the method. Hence the error.

low and high are already passed as parameters of your integrateF method and they are redeclared again inside the method..

And x is not assigned a value when it is using for the calculation of s..

double x, ans;
double s = 1/2*exp((-x*x)/2);