# C Real-Life Examples

## Practical Examples

This page contains a list of practical examples used in real world projects.

## Variables and Data Types

### Example

Use variables to store different data of a college student:

// Student data
int studentID = 15;
int studentAge = 23;
float studentFee = 75.25;

// Print variables
printf("Student id: %d\n", studentID);
printf("Student age: %d\n", studentAge);
printf("Student fee: %f\n", studentFee);
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### Example

Calculate the area of a rectangle (by multiplying the length and width)

// Create integer variables
int length = 4;
int width = 6;
int area;

// Calculate the area of a rectangle
area = length * width;

// Print the variables
printf("Length is: %d\n", length);
printf("Width is: %d\n", width);
printf("Area of the rectangle is: %d", area);
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### Example

Use different data types to calculate and output the total cost of a number of items:

// Create variables of different data types
int items = 50;
float cost_per_item = 9.99;
float total_cost = items * cost_per_item;
char currency = '\$';

// Print variables
printf("Number of items: %d\n", items);
printf("Cost per item: %.2f %c\n", cost_per_item, currency);
printf("Total cost = %.2f %c\n", total_cost, currency);
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### Example

Calculate the percentage of a user's score in relation to the maximum score in a game:

// Set the maximum possible score in the game to 500
int maxScore = 500;

// The actual score of the user
int userScore = 423;

// Calculate the percantage of the user's score in relation to the maximum available score
float percentage = (float) userScore / maxScore * 100.0;

// Print the percentage
printf("User's percentage is %.2f", percentage);
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For a tutorial about variables and data types in C, visit our Variables Chapter and Data Types Chapter.

## Booleans

### Example

Find out if a person is old enough to vote:

int myAge = 25;
int votingAge = 18;

printf("%d", myAge >= votingAge); // Returns 1 (true), meaning 25 year olds are allowed to vote!
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You could also wrap the code above in an `if...else` to perform different actions depending on the result:

### Example

Output "Old enough to vote!" if `myAge` is greater than or equal to `18`. Otherwise output "Not old enough to vote.":

int myAge = 25;
int votingAge = 18;

if (myAge >= votingAge) {
printf("Old enough to vote!");
} else {
printf("Not old enough to vote.");
}
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## Conditions (If..Else)

### Example

Use if..else statements to output some text depending on what time it is:

int time = 20;
if (time < 18) {
printf("Good day.");
} else {
printf("Good evening.");
}
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### Example

Check whether the user enters the correct code:

int doorCode = 1337;

if (doorCode == 1337) {
printf("Correct code.\nThe door is now open.");
} else {
printf("Wrong code.\nThe door remains closed.");
}
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### Example

Find out if a number is positive or negative:

int myNum = 10;

if (myNum > 0) {
printf("The value is a positive number.");
} else if (myNum < 0) {
printf("The value is a negative number.");
} else {
printf("The value is 0.");
}
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### Example

Find out if a person is old enough to vote:

int myAge = 25;
int votingAge = 18;

if (myAge >= votingAge) {
printf("Old enough to vote!");
} else {
printf("Not old enough to vote.");
}
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### Example

Find out if a number is even or odd:

int myNum = 5;

if (myNum % 2 == 0) {
printf("%d is even.\n", myNum);
} else {
printf("%d is odd.\n", myNum);
}
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## Switch

### Example

Use the weekday number to calculate and output the weekday name:

int day = 4;

switch (day) {
case 1:
printf("Monday");
break;
case 2:
printf("Tuesday");
break;
case 3:
printf("Wednesday");
break;
case 4:
printf("Thursday");
break;
case 5:
printf("Friday");
break;
case 6:
printf("Saturday");
break;
case 7:
printf("Sunday");
break;
}
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## While Loops

### Example

Use a while loop to create a simple "countdown" program:

int countdown = 3;

while (countdown > 0) {
printf("%d\n", countdown);
countdown--;
}

printf("Happy New Year!!\n");
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### Example

Use a while loop to play a game of Yatzy:

int dice = 1;

while (dice <= 6) {
if (dice < 6) {
printf("No Yatzy\n");
} else {
printf("Yatzy!\n");
}
dice = dice + 1;
}
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### Example

Use a while loop to reverse some numbers:

// A variable with some specific numbers
int numbers = 12345;

// A variable to store the reversed number
int revNumbers = 0;

// Reverse and reorder the numbers
while (numbers) {
// Get the last number of 'numbers' and add it to 'revNumber'
revNumbers = revNumbers * 10 + numbers % 10;
// Remove the last number of 'numbers'
numbers /= 10;
}
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## For Loops

### Example

Use a for loop to create a program that only print even values between 0 and 10:

int i;

for (i = 0; i <= 10; i = i + 2) {
printf("%d\n", i);
}
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### Example

Use a for loop to create a program that counts to 100 by tens:

for (i = 0; i <= 100; i += 10) {
printf("%d\n", i);
}
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### Example

Use a for loop to print the powers of 2 up to 512:

for (i = 2; i <= 512; i *= 2) {
printf("%d\n", i);
}
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### Example

Use a for loop to create a program that prints the multiplication table of a specified number (2 in this example):

int number = 2;
int i;

// Print the multiplication table for the number 2
for (i = 1; i <= 10; i++) {
printf("%d x %d = %d\n", number, i, number * i);
}

return 0;
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## Arrays

### Example

Create a program that calculates the average of different ages:

// An array storing different ages
int ages[] = {20, 22, 18, 35, 48, 26, 87, 70};

float avg, sum = 0;
int i;

// Get the length of the array
int length = sizeof(ages) / sizeof(ages[0]);

// Loop through the elements of the array
for (int i = 0; i < length; i++) {
sum += ages[i];
}

// Calculate the average by dividing the sum by the length
avg = sum / length;

// Print the average
printf("The average age is: %.2f", avg);
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### Example

Create a program that finds the lowest age among different ages:

// An array storing different ages
int ages[] = {20, 22, 18, 35, 48, 26, 87, 70};

// Get the length of the array
int length = sizeof(ages) / sizeof(ages[0]);

// Create a variable and assign the first array element of ages to it
int lowestAge = ages[0];

// Loop through the elements of the ages array to find the lowest age
for (int i = 0; i < length; i++) {
if (lowestAge > ages[i]) {
lowestAge = ages[i];
}
}
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## Strings

### Example

Use strings to create a simple welcome message:

char message[] = "Good to see you,";
char fname[] = "John";

printf("%s %s!", message, fname);
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### Example

Create a program that counts the number of characters found in a specific word:

char word[] = "Computer";
printf("The word '%s' has %d characters in it.", word, strlen(word));
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## User Input

### Example

Get the name of a user and print it:

char fullName[30];

fgets(fullName, sizeof(fullName), stdin);

printf("Hello %s", fullName);
Run example »

## Functions

### Example

Use a function to create a program that converts a value from fahrenheit to celsius:

// Function to convert Fahrenheit to Celsius
float toCelsius(float fahrenheit) {
return (5.0 / 9.0) * (fahrenheit - 32.0);
}

int main() {
// Set a fahrenheit value
float f_value = 98.8;

// Call the function with the fahrenheit value
float result = toCelsius(f_value);

// Print the fahrenheit value
printf("Fahrenheit: %.2f\n", f_value);

// Print the result
printf("Convert Fahrenheit to Celsius: %.2f\n", result);

return 0;
}
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## Structures

### Example

Use a structure to store and output different information about Cars:

struct Car {
char brand[50];
char model[50];
int year;
};

int main() {
struct Car car1 = {"BMW", "X5", 1999};
struct Car car2 = {"Ford", "Mustang", 1969};
struct Car car3 = {"Toyota", "Corolla", 2011};

printf("%s %s %d\n", car1.brand, car1.model, car1.year);
printf("%s %s %d\n", car2.brand, car2.model, car2.year);
printf("%s %s %d\n", car3.brand, car3.model, car3.year);

return 0;
}
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## Memory Management

### Example

struct list {
int *data; // Points to the memory where the list items are stored
int numItems; // Indicates how many items are currently in the list
int size; // Indicates how many items fit in the allocated memory
};

void addToList(struct list *myList, int item);

int main() {
struct list myList;
int amount;

// Create a list and start with enough space for 10 items
myList.numItems = 0;
myList.size = 10;
myList.data = malloc(myList.size * sizeof(int));

// Find out if memory allocation was successful
if (myList.data == NULL) {
printf("Memory allocation failed");
return 1; // Exit the program with an error code
}

// Add any number of items to the list specified by the amount variable
amount = 44;
for (int i = 0; i < amount; i++) {
}

// Display the contents of the list
for (int j = 0; j < myList.numItems; j++) {
printf("%d ", myList.data[j]);
}

// Free the memory when it is no longer needed
free(myList.data);
myList.data = NULL;

return 0;
}

// This function adds an item to a list
void addToList(struct list *myList, int item) {

// If the list is full then resize the memory to fit 10 more items
if (myList->numItems == myList->size) {
myList->size += 10;
myList->data = realloc( myList->data, myList->size * sizeof(int) );
}

// Add the item to the end of the list
myList->data[myList->numItems] = item;
myList->numItems++;
}
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