Arrays and loops

Learn to iterate over arrays with for.

Arrays and loops

A for loop is used to print all array elements. The counter serves as the array index.

int scores[5] = {85, 92, 78, 90, 88};
for (int i = 0; i < 5; i++) {
    printf("%d\n", scores[i]);
}

Here i goes from 0 to 4 and scores[i] accesses each element in turn. The loop bound must be i < 5; writing i <= 5 overflows. Computing the bound with the sizeof idiom is safer.

Computing a sum

You can sum all array elements with a loop. This is the basis for average, max, min and similar computations.

int scores[5] = {85, 92, 78, 90, 88};
int sum = 0;
for (int i = 0; i < 5; i++) {
    sum += scores[i];
}
printf("Sum: %d\n", sum);  // 433

Here sum starts at 0; each iteration adds one element. After the loop sum is 433. For the average, divide by 5.

Exercise Print the array with a loop

Write a C program. Declare int scores[5] = {85, 92, 78, 90, 88};. Use a for (int i = 0; i < 5; i++) loop to print each element with printf("%d\n", scores[i]);. Put #include <stdio.h> at the top.

Show example solution

#include <stdio.h>

int main(void) {
    int scores[5] = {85, 92, 78, 90, 88};
    for (int i = 0; i < 5; i++) {
        printf("%d\n", scores[i]);
    }
    return 0;
}

Test yourself

Complete the loop condition

for (int i = 0; i ____ 5; i++) {
    printf("%d", scores[i]);
}

Show answer

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

Match loop and array

i = 0

Init
i < n

Condition
i++

Increment
scores[i]

Element
What does sum += scores[i] do?
```
for (int i = 0; i < 5; i++) {
    sum += scores[i];
}
```
- Resets sum
- Adds scores[i] to sum
- Decrements scores[i]
- Stops the loop
Show answer

Adds scores[i] to sum — sum += scores[i] adds the element to sum.

Next lesson: Summary - Arrays

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