Unit 1: C programming fundamentals to file handling

c#include <stdio.h>
int main() {
    char ch;
    printf("Enter a character: ");
    scanf("%c", &ch);
    printf("ASCII value of %c = %d\n", ch, ch);
    printf("int: %zu, float: %zu, double: %zu, char: %zu bytes\n",
           sizeof(int), sizeof(float), sizeof(double), sizeof(char));
    return 0;
}

Printing a char with %d shows its ASCII code. sizeof gives the size of a type in bytes.

• Even or odd: if (n % 2 == 0) → even, else odd.
• Largest of three: compare with nested if or max = (a > b) ? (a > c ? a : c) : (b > c ? b : c);
• Prime check: a number n > 1 is prime if no number from 2 to √n divides it.

cint n, i, isPrime = 1;
scanf("%d", &n);
if (n < 2) isPrime = 0;
for (i = 2; i * i <= n; i++)
    if (n % i == 0) { isPrime = 0; break; }
printf(isPrime ? "Prime" : "Not prime");

• Multiplication table: for (i = 1; i <= 10; i++) printf("%d x %d = %d\n", n, i, n * i);
• Simple calculator with switch:

cchar op; float a, b;
scanf("%f %c %f", &a, &op, &b);
switch (op) {
    case '+': printf("%.2f", a + b); break;
    case '-': printf("%.2f", a - b); break;
    case '*': printf("%.2f", a * b); break;
    case '/': if (b != 0) printf("%.2f", a / b); else printf("Divide by zero"); break;
    default: printf("Invalid operator");
}

• Factorial using a function (iterative or recursive), largest of three using a function, and first 20 squares using a function that returns n × n.

clong factorial(int n) {
    long f = 1;
    for (int i = 2; i <= n; i++) f *= i;
    return f;
}

• Matrix addition: read two m × n matrices and add them with nested loops: c[i][j] = a[i][j] + b[i][j];
• String functions: use strlen, strcpy, strcmp and a reverse (with strrev or a manual swap loop).

c/* Reverse a string without strrev */
int len = strlen(s);
for (int i = 0; i < len / 2; i++) {
    char t = s[i]; s[i] = s[len - 1 - i]; s[len - 1 - i] = t;
}

• Pointer program: print a variable's value and address using & and *; swap with pointers.
• Structure vs union memory: print sizeof of a struct and a union with the same members to show the difference.
• Student I-card: a structure with name, roll number, course and address, printed in an ID-card layout.
• Employee file: write employee records with fprintf to a file and read them back with fscanf.

cFILE *fp = fopen("emp.txt", "w");
fprintf(fp, "%d %s %.2f\n", id, name, salary);
fclose(fp);