Looping over Arrays

We have an array of readings. We want to do something with each one. We could do

#include <stdio.h>

int main(void) {
    int readings[5] = { 80, 95, 60, 72, 88 };
    printf("%d\n", readings[0]);
    printf("%d\n", readings[1]);
    printf("%d\n", readings[2]);
    printf("%d\n", readings[3]);
    printf("%d\n", readings[4]);
    return 0;
}

Repetitive. Exactly what we said in earlier lessons to avoid

The classic C for loop goes hand in hand with arrays

#include <stdio.h>

int main(void) {
    int readings[5] = { 80, 95, 60, 72, 88 };

    for (int i = 0; i < 5; i++) {
        printf("%d\n", readings[i]);
    }

    return 0;
}

We used i < 5, not i <= 5. Why? Indices go from 0 to size - 1. For 5 elements, indices are 0, 1, 2, 3, 4. i = 5 would be out of bounds, and we already know how dangerous that is in C

Hardcoding 5 in the loop is fragile. If we add or remove an element, we have to remember to update the loop. Use the sizeof trick instead

#include <stdio.h>

int main(void) {
    int readings[] = { 80, 95, 60, 72, 88 };
    int n = sizeof(readings) / sizeof(readings[0]);

    for (int i = 0; i < n; i++) {
        printf("%d\n", readings[i]);
    }
    return 0;
}

Now the loop works no matter how many elements the array has. Add or remove a reading, run again, it just works

A classic pattern: summing numbers

#include <stdio.h>

int main(void) {
    int prices[] = { 10, 20, 30, 40 };
    int n = sizeof(prices) / sizeof(prices[0]);

    int total = 0;
    for (int i = 0; i < n; i++) {
        total = total + prices[i];
    }
    printf("%d\n", total);   // 100
    return 0;
}

Start with total = 0, walk through every element, add it. You will write this kind of loop many times in your career. Read it line by line and make sure you understand why it works

A note about functions and arrays: as we mentioned in the previous lesson, when you pass an array to a function, the sizeof trick stops working (the array becomes a pointer). The standard fix: pass the size as a separate parameter

#include <stdio.h>

void print_all(int arr[], int n) {
    for (int i = 0; i < n; i++) {
        printf("%d\n", arr[i]);
    }
}

int main(void) {
    int readings[] = { 80, 95, 60, 72, 88 };
    int n = sizeof(readings) / sizeof(readings[0]);
    print_all(readings, n);
    return 0;
}

This is a very common C idiom. Get used to writing it

Mission: The Tape Line Daily Register

The magnetic tape line sends a batch of readings for the current shift. The number of readings varies from day to day, so the first thing you receive is how many readings are coming.

Read an integer n from input: the number of readings
Read n integers into an array (use a loop for reading, with scanf inside it)
Print each reading on its own line (use a for loop)
Print the total of all the readings
Print the average (cast to double to avoid integer division: use (double) total / n)

Example

Input

5
80 95 60 72 88

Output

Example

Input

3
10 20 30

Output