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Status: Tags: Links: C Variables

C Arrays

• constant variable, fixed length
• Treated as pointers
  • Memory location is not needed to be known
• Variable of an int array is just an int pointer
• Each element in an array is stored in a continuous block, starting from array pos
• Jump in adress when iterating depends on the var type stored in the arr
• array[i] == *(array+i) where i is index
• Array parameters should be const
  • const int ONE = 1; or `int const ONE = 1;
• String arrays hold the pointers for the starts of each string
• Accessing outside bounds
  • Could lead to crash, or access of garbage data

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int arr[2] = {0, 1, 2} //stating size isn't necessary

//Changing Values
arr [2] = 3;
(array + 2) = 3; //equivalent

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Examples

Average of an array’s values

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float average(float ar[], int n) {
    float sum = 0; 

    for (int i = 0; i < n; i++) {
        sum += ar[i];
    }

    return sum / n; 
}

int main() {
    float arr[6] = {0.2, 4.5, 1.2, 5.5, 1.1, -1.2};
    float avg = average(arr, 6);
    return 0; 
}

Copy Array

Write a function that gets arrays of ints of length n and copies all data from one array into the other.

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void copy_arry(float* dest, const float* src, int n) {
    for (int i = 0; i < n; i++) {
       dest[i] = src[i];
    }
}

int main() {
    float arr[6] = {0.2, 4.5, 1.2, 5.5, 1.1, -1.2};
    float arr2[6] = {0.2, 4.5, 1.2, 5.5, 1.1, -1.2};

    copy_arry(arr, arr2, 6);
    return 0; 
}

Multidimensional Array

• So far we’ve only seen 1D arrays
• But often we need 2D / 3D arrays
• Examples:
  • Picture: Each entry in the array is the color of a pixel (.bmp format)
  • Temperature at each point in the room

Creating a 2D array

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int width = 640, height = 480;
int image[height][width];

Accessing a 2D array

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image[i][j] = 128; 
// ---- OR --- 
(*(image + i))[j] = 128 // each element of image is type of int[width] 
// the size of each element is sizeof(int)*width 

See multid_array.c

Q: Is the type int** is equivalent to int[][]

A: int** is

• Array of pointers
• Array of (1D) arrays, possibly different lengths
• Pointer to a pointer

References: C - Array of pointers (tutorialspoint.com)

Created:: 2021-09-13 15:35