Problem 10. Determine whether a vector is monotonically increasing

Where did I do wrong？Please help me！

You fail test 2, since the vector x has length 1, you never evaluate anything in your loop. This can be fixed by initializing tf before the loop.

Look into recursive solution instead of this loop.

Why are you incrementing the solution with i=i+1? The for loop automatically increments from 1 to n-1. You are also only really testing the last two values in the vector. Your function returns false for each pair in vector but overwrites tf = false with true when it reaches the last two entries. You need to break out of the loop if you detect one false.