C Arrays

An array stores many values of the same type under one name. Instead of making 5 variables for 5 marks, we make one array with 5 elements.

Declare and initialize

int marks[5];                       // 5 elements, no values yet
int scores[5] = {80, 65, 90, 72, 55};
int days[] = {1, 2, 3};             // size is 3 (counted automatically)

Each element has an index. The index starts from 0. So scores[0] is 80 and the last element scores[4] is 55.

#include <stdio.h>

int main(void) {
    int scores[5] = {80, 65, 90, 72, 55};

    printf("First: %d\n", scores[0]);
    printf("Last: %d\n", scores[4]);

    scores[1] = 70;            // change a value
    printf("Changed: %d\n", scores[1]);
    return 0;
}

Output:

Loop over an array

#include <stdio.h>

int main(void) {
    int scores[5] = {80, 65, 90, 72, 55};
    int size = sizeof(scores) / sizeof(scores[0]);
    int sum = 0;

    for (int i = 0; i < size; i++) {
        printf("scores[%d] = %d\n", i, scores[i]);
        sum += scores[i];
    }
    printf("Total = %d, Average = %.1f\n", sum, (float)sum / size);
    return 0;
}

Output:

Find the largest value

#include <stdio.h>

int main(void) {
    int a[] = {23, 91, 45, 67, 12};
    int max = a[0];

    for (int i = 1; i < 5; i++) {
        if (a[i] > max) {
            max = a[i];
        }
    }
    printf("Maximum = %d\n", max);
    return 0;
}

Output:

Read values from the user

#include <stdio.h>

int main(void) {
    int n[3];

    for (int i = 0; i < 3; i++) {
        scanf("%d", &n[i]);
    }
    printf("You entered: %d %d %d\n", n[0], n[1], n[2]);
    return 0;
}

Output:

Next: C Two Dimensional Arrays.

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