Different ways to Initialize all members of an array to the same value in C - GeeksforGeeks (2024)

An array is a collection of data that holds fixed number of values of same type. For example: if you want to store marks of 100 students, you can create an array for it.

int num[100];

How to declare an array in C?

Data_type array_name[size_of_array];

For example,

float num[10];

Below are some of the different ways in which all elements of an array can be initialized to the same value:

1. Initializer List: To initialize an array in C with the same value, the naive way is to provide an initializer list. We use this with small arrays.

   int num[5] = {1, 1, 1, 1, 1};

   This will initialize the num array with value 1 at all index.
   We may also ignore the size of the array:

   int num[ ] = {1, 1, 1, 1, 1}

   The array will be initialized to 0 in case we provide empty initializer list or just specify 0 in the initializer list.

   int num[5] = { }; // num = [0, 0, 0, 0, 0]int num[5] = { 0 }; // num = [0, 0, 0, 0, 0]

2. Designated Initializer: This initializer is used when we want to initialize a range with the same value. This is used only with GCC compilers.
   [ first . . . last ] = value;

   int num[5]={ [0 . . . 4 ] = 3 }; // num = { 3, 3, 3, 3, 3}

   We may also ignore the size of array:

   int num[ ]={ [0 . . . 4 ] = 3 }; // num = { 3, 3, 3, 3, 3}

3. Macros: For initializing a huge array with the same value we can use macros.
   #include<stdio.h>

   #define x1 1

   #define x2 x1, x1

   #define x4 x2, x2

   #define x8 x4, x4

   #define x16 x8, x8

   #define x32 x16, x16

   int main(void)

   {

   // array declaration

   int num[] = { x32, x8, x4, x1};

   int size = sizeof(num)/ sizeof(int); // 32+8+4+1= 45

   printf("The size of the array is %d\n", size);

   printf("The value of element in the array at index 5 is %d ",

   num[4]);

   return 0;

   }

   See Also

   Initialization - cppreference.comC++ Pair Container: A Comprehensive GuideRaster, Vector and Text - What's Really in My PDF?vector :: assign() in C++ STL - GeeksforGeeks

   See Also

   Different Ways to Initialize a Map in C++ - GeeksforGeeks

   Output:

   The size of the array is 45The value of element in the array at index 5 is 1

4. Using For Loop: We can also use for loop to initialize an array with the same value.
   #include<stdio.h>

   int main(void)

   {

   int size = 6;

   int val = 1;

   // array declaration

   int arr[size];

   int i;

   // initializing array elements

   for (i = 0; i < size ; i++){

   arr[i] = val;

   }

   // print array

   printf("The array is:");

   for (i = 0; i < size ; i++){

   printf("%d ", arr[i]);

   }

   return 0;

   }

   Output:

   The array is:1 1 1 1 1 1