#include <stdio.h>

int main() {
    int a, b, choice;
    char op;

    printf("Enter: a op b (e.g. 5 + 3): ");
    scanf("%d %c %d", &a, &op, &b);

    switch(op) {
        case '+': printf("Result = %d\n", a+b); break;
        case '-': printf("Result = %d\n", a-b); break;
        case '*': printf("Result = %d\n", a*b); break;
        case '/':
            if(b != 0)
                printf("Result = %d\n", a/b);
            else
                printf("Error: Divide by zero!\n");
            break;
        default: printf("Invalid operator!\n");
    }
    return 0;
}

/* break — exits loop immediately */
for (int i=1; i<=10; i++) {
    if (i == 5) break;   // stops at 5
    printf("%d ", i);
}
// Output: 1 2 3 4

/* continue — skips current iteration */
for (int i=1; i<=10; i++) {
    if (i % 2 == 0) continue; // skip even
    printf("%d ", i);
}
// Output: 1 3 5 7 9

#include <stdio.h>
int main() {
    int a[2][2]={{1,2},{3,4}};
    int b[2][2]={{5,6},{7,8}};
    int c[2][2];

    /* Matrix Addition */
    for (int i=0; i<2; i++) {
        for (int j=0; j<2; j++) {
            c[i][j] = a[i][j] + b[i][j];
            printf("%d ", c[i][j]);
        }
        printf("\n");
    }
    return 0;
}
/* Output:
6 8
10 12 */

#include <stdio.h>
#include <string.h>  /* For string functions */

int main() {
    char name[50];

    printf("Enter name: ");
    gets(name);   /* Read string with spaces */

    printf("Hello, %s!\n", name);
    printf("Length: %d\n", strlen(name));

    /* String functions */
    char s1[20]="Hello", s2[20]="World", s3[50];

    strcat(s1, s2);   /* Concatenate: "HelloWorld" */
    strcpy(s3, s1);   /* Copy s1 to s3 */
    strcmp(s1, s2);   /* 0 if equal */
    strupr(s1);       /* Convert to uppercase */
    strlwr(s1);       /* Convert to lowercase */
    return 0;
}

#include <stdio.h>

/* Define structure */
struct Student {
    int   rollno;
    char  name[50];
    float gpa;
};

int main() {
    /* Create structure variable */
    struct Student s1 = {101, "Ravi Kumar", 8.75};

    /* Access using dot operator */
    printf("Roll: %d\n",  s1.rollno);
    printf("Name: %s\n",  s1.name);
    printf("GPA:  %.2f\n", s1.gpa);

    /* Array of structures */
    struct Student class[60];  // 60 students!

    return 0;
}

union Data {
    int i;       // 4 bytes
    float f;     // 4 bytes
    char str[20]; // 20 bytes — union size = 20
};
/* All share the same memory! */

void counter() {
    static int count = 0;  // initialized ONCE
    count++;
    printf("Count = %d\n", count);
}
int main() {
    counter(); // Count = 1
    counter(); // Count = 2
    counter(); // Count = 3
}

#include <stdio.h>

int main() {
    FILE *fp;

    /* ── WRITE to file ── */
    fp = fopen("student.txt", "w"); // "w" = write mode
    if (fp == NULL) {
        printf("Error opening file!\n");
        return 1;
    }
    fprintf(fp, "Name: Ravi Kumar\n");
    fprintf(fp, "Roll: 101\n");
    fclose(fp);   // close after writing

    /* ── READ from file ── */
    fp = fopen("student.txt", "r"); // "r" = read mode
    char line[100];
    while (fgets(line, 100, fp) != NULL) {
        printf("%s", line);
    }
    fclose(fp);

    return 0;
}

/* Swap using pointers (call by reference) */
void swap(int *x, int *y) {
    int temp = *x;
    *x = *y;
    *y = temp;
}

int main() {
    int a=10, b=20;
    swap(&a, &b);   // pass ADDRESSES
    printf("a=%d b=%d\n", a, b);
    // Output: a=20 b=10
}

/* Arrays are ALWAYS passed by reference (pointer) */
void printArray(int arr[], int n) {
    for (int i=0; i<n; i++)
        printf("%d ", arr[i]);
}