The Largest Value

The third pattern finds the largest value. Imagine going through a pile of exam papers to find the best one. You pick up the first paper. Then you look at the others one by one, and whenever one is better than the paper in your hand, you take that one instead. At the end, you're holding the best paper. In code, the paper in your hand is a variable:

int scores[] = {72, 45, 90, 38, 64};
int count = sizeof(scores) / sizeof(scores[0]);
int highest = scores[0];
for (int i = 1; i < count; i++) {
    if (scores[i] > highest) {
        highest = scores[i];
    }
}
printf("Highest score: %d\n", highest);

This prints:

Highest score: 90

The variable highest starts with the first element. That's why the loop can start at index 1: there's no need to compare the first element with itself (starting at 0 would work too). 45 is not greater than 72, but 90 is, so highest becomes 90. Neither 38 nor 64 is greater than 90, so 90 stays until the end.

Why not start with 0? Because 0 might not be one of the values. If all the values were negative, for example the winter temperatures {-5, -2, -8}, the starting 0 would stay the largest, and the program would print 0, a temperature that isn't in the array at all. The first element is always a safe start.

You find the smallest value the same way, only with < instead of >.

Sometimes you also need to know where the largest value is. Then keep its index in a second variable, and change both variables together:

int scores[] = {72, 45, 90, 38, 64};
int count = sizeof(scores) / sizeof(scores[0]);
int highest = scores[0];
int best_index = 0;
for (int i = 1; i < count; i++) {
    if (scores[i] > highest) {
        highest = scores[i];
        best_index = i;
    }
}
printf("Student %d has the most points: %d\n", best_index + 1, highest);

This prints:

Student 3 has the most points: 90

best_index starts at 0, the index of the first element, and changes whenever highest does. At the end, it's 2, so the student's number, counted from 1, is best_index + 1.