Lesson 10.2. Null terminated string

Introduction

The particularity of strings compared to character arrays is that a string ends with a trailing zero. This zero zero at the end of the string corresponds to the first character of the ASCII table (not to be confused with the character '0' which has ASCII code 48). The character at the end of the string is not necessarily in the last cell of the array. Let's analyze the following string:

char text[8] = "Bye!";

Here is how this string is stored in memory:

We can see that the zero at the end of the string is in the fifth cell which is not the last cell of the array. We can also see that the last 3 cells of the table contain arbitrary values, i.e. they are not are not initialized.

Syntax

The end of string character can be represented in different ways:

• as a decimal number: 0
• as an hexadecimal number: 0x00
• as a character: '\0'

The zero at the end of the string solves the problem of passing parameters to functions. No need to add a second parameter for the size, it is the zero that indicates the end of the string.

Exercise

Exercise 1

We give the following string declaration:

char str[10] = "abc";

Using a loop, iterate through the characters of the string one by one and display them as :

• characters
• decimal
• hexadecimal

Use sizeof() in the loop to get the array size. Here is the expected output:

str[0]  = 'a'   = 97    = 0x61
str[1]  = 'b'   = 98    = 0x62
str[2]  = 'c'   = 99    = 0x63
str[3]  = ''    =  0    = 0x00
str[4]  = ''    =  0    = 0x00
str[5]  = ''    =  0    = 0x00
str[6]  = ''    =  0    = 0x00
str[7]  = ''    =  0    = 0x00
str[8]  = ''    =  0    = 0x00
str[9]  = ''    =  0    = 0x00

#include <stdio.h> int main(void) { // Create the string int i; char str[10] = "abc"; // Display each character of str // COMPLETE HERE return 0; }

Exercise 2

We provide the following string declaration:

char str[] = "This string is too long because it contains too many characters.";

In one instruction, truncate the string after the 23th character. Display the string before and after :

Before : This string is too long because it contains too many characters.
After  : This string is too long

#include <stdio.h> int main(void) { // Create a long string char str[] = "This string is too long because it contains too many characters."; // Display the original string printf ("Before : %s\n", str); // Truncate after the 23th character. // COMPLETER ICI // Display the truncated string printf ("After : %s\n", str); return 0; }

Exercise 3

We provide the declaration of a string. We will assume that the string will never contain accents, cedilla, etc.

// Declaration of the string
char str[ ] = "This text should be capitalized.";

Complete the program below that converts each lowercase character in the string to uppercase. Note that it is converting the string and not just displaying it in upper case. Here is the expected result:

Before: This text should be capitalized.
After : THIS TEXT SHOULD BE CAPITALIZED.

#include <stdio.h> int main(void) { // Declaration of the string char str[ ] = "This text should be capitalized."; // COMPLETE HERE printf("After : %s\n", str); return 0; }

Quiz

A string always ends with ....

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What is the size of the following array:

char str[] = "abc";

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How many useful characters can the following string contain:

char str[8];

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Which syntaxes insert a trailing zero to mark the end of a string?

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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 9.2. Array initialization
• 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 10.3. 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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