C Programming: Arrays, Structures, and File Handling Examples

C

 

1. Display Even Numbers from Array

#include 
int main() {
    int n, arr[50];
    printf("Enter number of elements: ");
    scanf("%d", &n);
    printf("Enter %d elements: ", n);
    for(int i = 0; i < n; i++)
        scanf("%d", &arr[i]);
    printf("Even numbers: ");
    for(int i = 0; i < n; i++)
        if(arr[i] % 2 == 0)
            printf("%d ", arr[i]);
    return 0;
}

Output:
Enter number of elements: 5
Enter 5 elements: 1 2 3 4 5
Even numbers: 2 4

2. Find Total and Average of Array Elements

#include 
int main() {
    int n, arr[50], sum = 0;
    float avg;
    printf("Enter number of elements: ");
    scanf("%d", &n);
    printf("Enter %d elements: ", n);
    for(int i = 0; i < n; i++) {
        scanf("%d", &arr[i]);
        sum += arr[i];
    }
    avg = (float)sum / n;
    printf("Total: %d\nAverage: %.2f", sum, avg);
    return 0;
}

Output:
Enter number of elements: 4
Enter 4 elements: 10 20 30 40
Total: 100
Average: 25.00

3. Display Array in Reverse Order

#include 
int main() {
    int n, arr[50];
    printf("Enter number of elements: ");
    scanf("%d", &n);
    printf("Enter %d elements: ", n);
    for(int i = 0; i < n; i++)
        scanf("%d", &arr[i]);
    printf("Array in reverse order: ");
    for(int i = n-1; i >= 0; i--)
        printf("%d ", arr[i]);
    return 0;
}

Output:
Enter number of elements: 5
Enter 5 elements: 1 2 3 4 5
Array in reverse order: 5 4 3 2 1

4. Count Positive, Negative, Even, and Odd Numbers

#include 
int main() {
    int n, arr[50], pos = 0, neg = 0, even = 0, odd = 0;
    printf("Enter number of elements: ");
    scanf("%d", &n);
    printf("Enter %d elements: ", n);
    for(int i = 0; i < n; i++) {
        scanf("%d", &arr[i]);
        if(arr[i] > 0) pos++;
        else if(arr[i] < 0) neg++;
        if(arr[i] % 2 == 0) even++;
        else odd++;
    }
    printf("Positive: %d\nNegative: %d\nEven: %d\nOdd: %d", pos, neg, even, odd);
    return 0;
}

Output:
Enter number of elements: 6
Enter 6 elements: 1 -2 3 -4 5 6
Positive: 4
Negative: 2
Even: 3
Odd: 3

5. Copy Array Elements to Another Array

#include 
int main() {
    int n, arr1[50], arr2[50];
    printf("Enter number of elements: ");
    scanf("%d", &n);
    printf("Enter %d elements: ", n);
    for(int i = 0; i < n; i++)
        scanf("%d", &arr1[i]);
    for(int i = 0; i < n; i++)
        arr2[i] = arr1[i];
    printf("Copied array: ");
    for(int i = 0; i < n; i++)
        printf("%d ", arr2[i]);
    return 0;
}

Output:
Enter number of elements: 4
Enter 4 elements: 10 20 30 40
Copied array: 10 20 30 40

6. Add Two Matrices

#include 
int main() {
    int r, c, a[10][10], b[10][10], sum[10][10];
    printf("Enter rows and columns: ");
    scanf("%d %d", &r, &c);
    printf("Enter first matrix elements:\n");
    for(int i = 0; i < r; i++)
        for(int j = 0; j < c; j++)
            scanf("%d", &a[i][j]);
    printf("Enter second matrix elements:\n");
    for(int i = 0; i < r; i++)
        for(int j = 0; j < c; j++)
            scanf("%d", &b[i][j]);
    for(int i = 0; i < r; i++)
        for(int j = 0; j < c; j++)
            sum[i][j] = a[i][j] + b[i][j];
    printf("Sum of matrices:\n");
    for(int i = 0; i < r; i++) {
        for(int j = 0; j < c; j++)
            printf("%d ", sum[i][j]);
        printf("\n");
    }
    return 0;
}

Output:
Enter rows and columns: 2 2
Enter first matrix elements:
1 2
3 4
Enter second matrix elements:
5 6
7 8
Sum of matrices:
6 8
10 12

7. Subtract Two Matrices

#include 
int main() {
    int r, c, a[10][10], b[10][10], diff[10][10];
    printf("Enter rows and columns: ");
    scanf("%d %d", &r, &c);
    printf("Enter first matrix elements:\n");
    for(int i = 0; i < r; i++)
        for(int j = 0; j < c; j++)
            scanf("%d", &a[i][j]);
    printf("Enter second matrix elements:\n");
    for(int i = 0; i < r; i++)
        for(int j = 0; j < c; j++)
            scanf("%d", &b[i][j]);
    for(int i = 0; i < r; i++)
        for(int j = 0; j < c; j++)
            diff[i][j] = a[i][j] - b[i][j];
    printf("Difference of matrices:\n");
    for(int i = 0; i < r; i++) {
        for(int j = 0; j < c; j++)
            printf("%d ", diff[i][j]);
        printf("\n");
    }
    return 0;
}

Output:
Enter rows and columns: 2 2
Enter first matrix elements:
5 6
7 8
Enter second matrix elements:
1 2
3 4
Difference of matrices:
4 4
4 4

8. Convert Positive to Negative and Vice Versa

#include 
int main() {
    int n, arr[50];
    printf("Enter number of elements: ");
    scanf("%d", &n);
    printf("Enter %d elements: ", n);
    for(int i = 0; i < n; i++)
        scanf("%d", &arr[i]);
    printf("Converted array: ");
    for(int i = 0; i < n; i++) {
        arr[i] = -arr[i];
        printf("%d ", arr[i]);
    }
    return 0;
}

Output:
Enter number of elements: 5
Enter 5 elements: 1 -2 3 -4 5
Converted array: -1 2 -3 4 -5

9. Multiply Two Matrices

#include 
int main() {
    int r1, c1, r2, c2, a[10][10], b[10][10], prod[10][10];
    printf("Enter rows and columns for first matrix: ");
    scanf("%d %d", &r1, &c1);
    printf("Enter rows and columns for second matrix: ");
    scanf("%d %d", &r2, &c2);
    if(c1 != r2) {
        printf("Matrix multiplication not possible!\n");
        return 0;
    }
    printf("Enter first matrix elements:\n");
    for(int i = 0; i < r1; i++)
        for(int j = 0; j < c1; j++)
            scanf("%d", &a[i][j]);
    printf("Enter second matrix elements:\n");
    for(int i = 0; i < r2; i++)
        for(int j = 0; j < c2; j++)
            scanf("%d", &b[i][j]);
    for(int i = 0; i < r1; i++)
        for(int j = 0; j < c2; j++) {
            prod[i][j] = 0;
            for(int k = 0; k < c1; k++)
                prod[i][j] += a[i][k] * b[k][j];
        }
    printf("Product of matrices:\n");
    for(int i = 0; i < r1; i++) {
        for(int j = 0; j < c2; j++)
            printf("%d ", prod[i][j]);
        printf("\n");
    }
    return 0;
}

Output:
Enter rows and columns for first matrix: 2 2
Enter rows and columns for second matrix: 2 2
Enter first matrix elements:
1 2
3 4
Enter second matrix elements:
5 6
7 8
Product of matrices:
19 22
43 50

10. String Length Using String Function

#include 
#include 
int main() {
    char str[50];
    printf("Enter a string: ");
    scanf("%s", str);
    printf("Length of string: %d\n", strlen(str));
    return 0;
}

Output:
Enter a string: Hello
Length of string: 5

11. String Length Without String Function

#include 
int main() {
    char str[50];
    int len = 0;
    printf("Enter a string: ");
    scanf("%s", str);
    while(str[len] != '\0')
        len++;
    printf("Length of string: %d\n", len);
    return 0;
}

Output:
Enter a string: World
Length of string: 5

12. Check if String is Palindrome

#include 
#include 
int main() {
    char str[50];
    int len, isPal = 1;
    printf("Enter a string: ");
    scanf("%s", str);
    len = strlen(str);
    for(int i = 0; i < len/2; i++) {
        if(str[i] != str[len-1-i]) {
            isPal = 0;
            break;
        }
    }
    if(isPal)
        printf("String is a palindrome!\n");
    else
        printf("String is not a palindrome\n");
    return 0;
}

Output:
Enter a string: radar
String is a palindrome!

13. Swap Two Variables Using Pointer and Function

#include 
void swap(int *a, int *b) {
    int temp = *a;
    *a = *b;
    *b = temp;
}
int main() {
    int x, y;
    printf("Enter two numbers: ");
    scanf("%d %d", &x, &y);
    printf("Before swap: x = %d, y = %d\n", x, y);
    swap(&x, &y);
    printf("After swap: x = %d, y = %d\n", x, y);
    return 0;
}

Output:
Enter two numbers: 5 10
Before swap: x = 5, y = 10
After swap: x = 10, y = 5

14. Area of Circle Using Pointer and Function

#include 
#define PI 3.14159
void area(float *r, float *a) {
    *a = PI * (*r) * (*r);
}
int main() {
    float radius, area_result;
    printf("Enter radius: ");
    scanf("%f", &radius);
    area(&radius, &area_result);
    printf("Area of circle: %.2f\n", area_result);
    return 0;
}

Output:
Enter radius: 5
Area of circle: 78.54

15. Find Maximum and Minimum Using Pointer to Function

#include 
void findMaxMin(int arr[], int n, int *max, int *min) {
    *max = *min = arr[0];
    for(int i = 1; i < n; i++) {
        if(arr[i] > *max) *max = arr[i];
        if(arr[i] < *min) *min = arr[i];
    }
}
int main() {
    int n, arr[50], max, min;
    printf("Enter number of elements: ");
    scanf("%d", &n);
    printf("Enter %d elements: ", n);
    for(int i = 0; i < n; i++)
        scanf("%d", &arr[i]);
    findMaxMin(arr, n, &max, &min);
    printf("Maximum: %d\nMinimum: %d\n", max, min);
    return 0;
}

Output:
Enter number of elements: 5
Enter 5 elements: 10 5 20 15 8
Maximum: 20
Minimum: 5

16. Sum and Average Using Dynamic Array

#include 
#include 
int main() {
    int n, *arr, sum = 0;
    float avg;
    printf("Enter number of elements: ");
    scanf("%d", &n);
    arr = (int *)malloc(n * sizeof(int));
    printf("Enter %d elements: ", n);
    for(int i = 0; i < n; i++) {
        scanf("%d", &arr[i]);
        sum += arr[i];
    }
    avg = (float)sum / n;
    printf("Sum: %d\nAverage: %.2f\n", sum, avg);
    free(arr);
    return 0;
}

Output:
Enter number of elements: 4
Enter 4 elements: 10 20 30 40
Sum: 100
Average: 25.00

17. Sum of Prime Numbers Using Dynamic Array

#include 
#include 
int isPrime(int num) {
    if(num <= 1) return 0;
    for(int i = 2; i * i <= num; i++)
        if(num % i == 0) return 0;
    return 1;
}
int main() {
    int n, *arr, sum = 0;
    printf("Enter number of elements: ");
    scanf("%d", &n);
    arr = (int *)malloc(n * sizeof(int));
    printf("Enter %d elements: ", n);
    for(int i = 0; i < n; i++) {
        scanf("%d", &arr[i]);
        if(isPrime(arr[i]))
            sum += arr[i];
    }
    printf("Sum of prime numbers: %d\n", sum);
    free(arr);
    return 0;
}

Output:
Enter number of elements: 5
Enter 5 elements: 2 3 4 5 6
Sum of prime numbers: 10

1. Add Two Complex Numbers by Passing Structure to a Function

#include 
struct Complex {
    float real, imag;
};
struct Complex addComplex(struct Complex c1, struct Complex c2) {
    struct Complex sum;
    sum.real = c1.real + c2.real;
    sum.imag = c1.imag + c2.imag;
    return sum;
}
int main() {
    struct Complex c1, c2, result;
    printf("Enter real and imaginary parts of first complex number: ");
    scanf("%f %f", &c1.real, &c1.imag);
    printf("Enter real and imaginary parts of second complex number: ");
    scanf("%f %f", &c2.real, &c2.imag);
    result = addComplex(c1, c2);
    printf("Sum = %.2f + %.2fi\n", result.real, result.imag);
    return 0;
}

Output:
Enter real and imaginary parts of first complex number: 3 4
Enter real and imaginary parts of second complex number: 2 5
Sum = 5.00 + 9.00i

2. Demonstrate Difference Between Structure and Union

#include 
struct StructExample {
    int a;
    char b;
};
union UnionExample {
    int a;
    char b;
};
int main() {
    struct StructExample s;
    union UnionExample u;
    printf("Size of structure: %d bytes\n", sizeof(s));
    printf("Size of union: %d bytes\n", sizeof(u));
    s.a = 65; s.b = 'B';
    printf("Structure: a = %d, b = %c\n", s.a, s.b);
    u.a = 65;
    printf("Union after setting a: a = %d, b = %c\n", u.a, u.b);
    u.b = 'B';
    printf("Union after setting b: a = %d, b = %c\n", u.a, u.b);
    return 0;
}

Output:
Size of structure: 8 bytes
Size of union: 4 bytes
Structure: a = 65, b = B
Union after setting a: a = 65, b = A
Union after setting b: a = 66, b = B

3. Compare Two Dates Using Structure

#include 
struct Date {
    int day, month, year;
};
int main() {
    struct Date d1, d2;
    printf("Enter first date (dd mm yyyy): ");
    scanf("%d %d %d", &d1.day, &d1.month, &d1.year);
    printf("Enter second date (dd mm yyyy): ");
    scanf("%d %d %d", &d2.day, &d2.month, &d2.year);
    if(d1.day == d2.day && d1.month == d2.month && d1.year == d2.year)
        printf("Equal\n");
    else
        printf("Not Equal\n");
    return 0;
}

Output:
Enter first date (dd mm yyyy): 10 06 2023
Enter second date (dd mm yyyy): 10 06 2023
Equal

4. Demonstrate Nested Structure

#include 
struct Address {
    char city[20];
    int pin;
};
struct Person {
    char name[20];
    struct Address addr;
};
int main() {
    struct Person p;
    printf("Enter name: ");
    scanf("%s", p.name);
    printf("Enter city and pin code: ");
    scanf("%s %d", p.addr.city, &p.addr.pin);
    printf("Name: %s\nCity: %s\nPin: %d\n", p.name, p.addr.city, p.addr.pin);
    return 0;
}

Output:
Enter name: John
Enter city and pin code: Delhi 110001
Name: John
City: Delhi
Pin: 110001

5. Copy Content of a Text File

#include 
int main() {
    FILE *source, *dest;
    char ch;
    source = fopen("source.txt", "r");
    if(source == NULL) {
        printf("Source file not found!\n");
        return 1;
    }
    dest = fopen("copy.txt", "w");
    if(dest == NULL) {
        printf("Cannot create destination file!\n");
        fclose(source);
        return 1;
    }
    while((ch = fgetc(source)) != EOF)
        fputc(ch, dest);
    printf("File copied successfully!\n");
    fclose(source);
    fclose(dest);
    return 0;
}

Output (assuming source.txt contains "Hello World"):
File copied successfully!
(copy.txt will contain: Hello World)

6. Append Content to a File

#include 
int main() {
    FILE *file;
    char str[100];
    file = fopen("demo.txt", "a");
    if(file == NULL) {
        printf("Cannot open file!\n");
        return 1;
    }
    printf("Enter text to append: ");
    scanf(" %[^\n]", str);
    fprintf(file, "%s\n", str);
    printf("Content appended successfully!\n");
    fclose(file);
    return 0;
}

Output:
Enter text to append: New Line
Content appended successfully!

7. Write String to File and Reverse to Another File

#include 
#include 
int main() {
    FILE *demo, *reverse;
    char str[100];
    printf("Enter a string: ");
    scanf(" %[^\n]", str);
    demo = fopen("demo.txt", "w");
    if(demo == NULL) {
        printf("Cannot create demo.txt!\n");
        return 1;
    }
    fprintf(demo, "%s", str);
    fclose(demo);
    demo = fopen("demo.txt", "r");
    reverse = fopen("reverse.txt", "w");
    if(demo == NULL || reverse == NULL) {
        printf("File error!\n");
        return 1;
    }
    int len = strlen(str);
    for(int i = len-1; i >= 0; i--)
        fputc(str[i], reverse);
    printf("String reversed and saved!\n");
    fclose(demo);
    fclose(reverse);
    return 0;
}

Output:
Enter a string: Hello
String reversed and saved!
(demo.txt: Hello, reverse.txt: olleH)

8. Reverse Case of Text File Content

#include 
#include 
int main() {
    FILE *input, *output;
    char ch;
    input = fopen("input.txt", "r");
    if(input == NULL) {
        printf("Input file not found!\n");
        return 1;
    }
    output = fopen("output.txt", "w");
    if(output == NULL) {
        printf("Cannot create output file!\n");
        fclose(input);
        return 1;
    }
    while((ch = fgetc(input)) != EOF) {
        if(isupper(ch))
            fputc(tolower(ch), output);
        else if(islower(ch))
            fputc(toupper(ch), output);
        else
            fputc(ch, output);
    }
    printf("Content converted and saved!\n");
    fclose(input);
    fclose(output);
    return 0;
}

Output (assuming input.txt contains "Hello World"):
Content converted and saved!
(output.txt: hELLO wORLD)

9. Count Total Words in a Text File

#include 
#include 
int main() {
    FILE *file;
    char ch;
    int word_count = 0, in_word = 0;
    file = fopen("input.txt", "r");
    if(file == NULL) {
        printf("File not found!\n");
        return 1;
    }
    while((ch = fgetc(file)) != EOF) {
        if(isspace(ch) || ch == '\n' || ch == '\t') {
            in_word = 0;
        } else if(in_word == 0) {
            in_word = 1;
            word_count++;
        }
    }
    printf("Total words: %d\n", word_count);
    fclose(file);
    return 0;
}

Output (assuming input.txt contains "Hello World This is a test"):
Total words: 6


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