Lesson 9.2. Array initialization

Syntax

In C, an array can be initialized in its entirety at the time of its declaration and only at the time of its declaration. The syntax consists in putting between two braces the values of the cells separated by commas:

int tab[5] = { 12, 25, 65, 11, 7};

This initialization creates an array with the following values:

$$ tab = \begin{bmatrix} 12 \\ 25 \\ 65 \\ 11 \\ 7 \end{bmatrix} $$

If the number of values between the braces is less than the size of the table, only the first cells (concerned) will be initialized.

When initializing at the declaration, if the size of the table is not specified between the square brackets, the size of the table will automatically adapt. For example, the following line creates an array of 3 cells:

int tab[] = {1,2,3};

If you have to initialize an array outside its declaration, you have to

• either initialize it cell by cell ;
• or copy a memory block directly with the memcpy() function.

Exercises

Exercise 1

Write a program that creates declares and initializes an array with the first 5 odd numbers. The program then displays the contents of the array according to this example:

tab[0] = 1
tab[1] = 3
tab[2] = 5
tab[3] = 7
tab[4] = 9

#include <stdio.h> int main(void) { int i; // Create and initialize an array with 5 cells // COMPLETE HERE // Display the array // COMPLETE HERE return 0; }

Exercise 2

Modify the code of the previous exercise so that the table now contains the 1000 first odd numbers :

tab[0] = 1
tab[1] = 3
tab[2] = 5
...
tab[997] = 1995
tab[998] = 1997
tab[999] = 1999

#include <stdio.h> int main(void) { int i; // Declare an array with 1000 cells // COMPLETE HERE // Initialize the array with the 1000 first odd numbers // COMPLETE HERE // Display the array // COMPLETE HERE return 0; }

Quiz

Which syntaxes can be used for initializing an array?

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How to initialize an array outside its declaration?

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Let's consider the following initialization. What is in tab[2]?

int tab[3] = { 10, 20 };

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What is the size of this array?

char tab[] = { 10, 20, 30, 40 };

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See also

• Learn C programming
• Lesson 1.1. History of C programming language
• Lesson 1.2. First program
• Lesson 1.3. Compilation
• Lesson 1.4. Preprocessor directives
• Lesson 1.5. Which compiler to choose?
• Lesson 1.6. Flowchart
• Lesson 2.1. Types and variables
• Lesson 2.2. Integers
• Lesson 2.3. Floating point numbers
• Lesson 2.4. Characters
• Lesson 2.5. Variables initialization
• Lesson 2.6. Ariane flight 501
• Lesson 3.1. Arithmetic operators
• Lesson 3.2. modulo
• Lesson 3.3. Operators and types
• Lesson 3.4. Type casting
• Lesson 3.5. Bitwise operators
• Lesson 3.6. Bitwise operators details
• Lesson 3.7. Shifting operators
• Lesson 3.8. Assignment operators
• Lesson 3.9. Increment and decrement operators
• Lesson 3.10. Comparison operators
• Lesson 3.11. Logical operators
• Lesson 3.12. Operator precedence
• Lesson 4.1. printf
• Lesson 4.2. scanf
• Lesson 4.3. putchar
• Lesson 5.1. Conditional branching (if...else)
• Lesson 5.2. Nested if and indentation
• Lesson 5.3. Checking intervals
• Lesson 5.4. Ternary Operator ?:
• Lesson 5.5. switch..case statement
• Lesson 5.6. Break keyword in switch..case
• Lesson 6.1. do..while loop in C
• Lesson 6.2. While loop in C
• Lesson 6.3. For loop in C
• Lesson 6.4. How to choose the right loop in C ?
• Lesson 6.5. Exercices on loops in C
• Lesson 7.1. Bit masking
• Lesson 7.2. Bit masking, how to clear a bit in C?
• Lesson 7.3. Bit masking, how to set a bit in C?
• Lesson 7.4. Bit masking, how to toggle a bit in C?
• Lesson 7.5. Bit masking, how to check a single bit in C?
• Lesson 7.6. Overview of bit masking
• Lesson 8.1. Basic syntax of C functions
• Lesson 8.2. Calling C functions
• Lesson 8.3. Void keyword
• Lesson 8.4. Return keyword
• Lesson 8.5. Variable scope
• Lesson 8.6. Global variables
• Lesson 8.7. Static variables
• Lesson 8.8. Random numbers in C
• Lesson 8.9. Mathematical functions in C
• Lesson 9.1. Syntax of C arrays
• Lesson 9.3. Multidimensional arrays
• Lesson 9.4. How C arrays are stored in memory?
• Lesson 9.5. Arrays and functions
• Lesson 9.6. Exercises on C arrays
• Lesson 10.1. Strings in C
• Lesson 10.2. Null terminated string
• Lesson 10.3. The string.h library
• Lesson 10.4. String and functions
• Lesson 11.1. Introduction to pointers in C
• Lesson 11.2. Syntax of C pointers
• Lesson 11.3. Dynamic memory allocation
• Lesson 11.4. Incrementing pointers
• Lesson 11.5. Pointers as function argument in C
• Lesson 12.1. Introduction to structures in C
• Lesson 12.2. Properties of structures in C
• Lesson 12.3. Structures and pointers
• Lesson 12.4. Structures and functions
• Lesson 13.1. Recursive functions in C
• Lesson 13.2. Depth of recursive functions
• Lesson 13.2. Mutual recursion
• Lesson 14.1. Additional exercises

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