Negative in the middle
Input
find_first_negative([1, 2, -3, 4])
Output
2
The first negative number is -3 at index 2.
Full lesson preview
Find First Negative
Search a list to find the index of the first negative number.
Python practice8 minLoops & IterationBeginnerLast updated March 15, 2026
Problem statement
Given a list of integers, return the index (0-based) of the first negative number. If there are no negative numbers, return -1.
Task
Use iteration to locate the first element satisfying a condition and return its index.
Examples
Input format
A list of integers.
Output format
An integer representing the index of the first negative, or -1 if none.
Constraints
Do not use built-in functions that directly find index by predicate. Aim for O(n) time and O(1) extra space.
Samples
Sample 1
Input
find_first_negative([-1, 2, -3])
Output
0
The very first element is negative, so return index 0.