Lesson 10.4. String and functions

Explanations

Strings inherit the properties of character arrays. The same is true if the string is an argument to a function. The latter can then modify the content of the string (unless the argument is declared with const). However, thanks to the NULL character at the end of the string, it is not necessary to add a second parameter to specify the size of the string.

Example

The ucfirst() function below capitalizes the first character of the string str:

void ucfirst(char str[]) {
  if (str[0]<'a' || str[0]>'z') return;
  str[0] += 'A' - 'a';
}

The string is passed in parameters as an array of characters.

Exercises

Exercise 1

Write a function str_2_upper() that converts the string passed as parameter to uppercase.

For example:

Enter a text: Bonjour !           
In capital letters: BONJOUR !

#include <stdio.h> // Convert a string to uppercase void str_2_upper(char s[]); int main(void) { char str[100]; // Ask for a string printf ("Enter a text: "); fgets(str, 100, stdin); // Convert a text to uppercase // COMPLETE HERE // Affiche le texte en majuscule // COMPLETE HERE return 0; } // Convert a string to uppercase void str_2_upper(char s[]) { // COMPLETE HERE }

Exercise 2

Write a function nbSpace() that returns the number of spaces in a string. Here is the expected output of the program:

The text "To be or not to be..." contains 5 space(s).

#include <stdio.h> // Return the number of spaces in the string // COMPLETE HERE int main(void) { char shakespear[] = "To be or not to be..."; // Display the number of spaces printf ("The text \"%s\" contains %d space(s).\n", shakespear, nbSpace(shakespear)); return 0; } // Return the number of spaces in the string // COMPLETE HERE

Exercise 3

Write a function int isCharIn(char s[], char needle) that returns the number of occurrences needle in the string s. Here is the expected output of the program:

The text "To be or not to be..." contains 4 'o' and 2 'e'.

#include <stdio.h> // Count the number of occurrences of needle in s // COMPLETE HERE int main(void) { char shakespear[] = "To be or not to be..."; // Display the number of 'o' and 'e' in the string // COMPLETE HERE return 0; } // Count the number of occurrences of needle in s int isCharIn(const char s[], char needle) { // COMPLETE HERE }

Exercise 4

Write a char palindrome() function that returns:

• 1 if the string s is a palindrome;
• 0 otherwise.

Enter a word: radar
radar is a palindrome.

Enter a word: pifometer
pifometer is not a palindrome.

#include <stdio.h> #include <string.h> // Returns 1 if the string s is a palindrome // COMPLETE HERE int main(void) { char mot[20]; // Ask for a word printf("Enter a word: "); scanf("%20s", mot); // Check if the word is a palindrome // COMPLETE HERE return 0; } // Returns 1 if the string s is a palindrome // COMPLETE HERE

Quiz

To pass a string as a parameter in a function ...

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A character string passed as a parameter in a function ...

char *strcpy(char *s1, const char *s2);

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A string passed into a function (without const) can be expanded ...

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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 10.2. Null terminated string
• Lesson 10.3. The string.h library
• 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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