Unit 2: Control structures and functions

• if: runs a block only if the condition is true.
• if-else: chooses between two blocks.
• Nested if / else-if ladder: tests several conditions in order.
• switch: selects one of many cases by the value of an integer or character expression; each case usually ends with break.

cint day = 3;
switch (day) {
    case 1: printf("Monday"); break;
    case 2: printf("Tuesday"); break;
    case 3: printf("Wednesday"); break;
    default: printf("Invalid day");
}

A loop repeats a block of statements while a condition holds.

c/* Sum of first n natural numbers */
int n = 10, sum = 0;
for (int i = 1; i <= n; i++) {
    sum += i;
}
printf("Sum = %d", sum);   /* 55 */

• break ends the loop (or switch) immediately and jumps to the statement after it.
• continue skips the rest of the current iteration and moves to the next one.

• goto: transfers control to a labelled statement — legal but discouraged because it makes programs hard to follow; occasionally used to exit deeply nested loops.

A function is a self-contained block of code that performs a specific task. Functions reduce repetition, make programs easier to read and debug, and allow reuse.

• Function prototype (declaration): tells the compiler the name, return type and parameter types: int add(int, int);
• Function definition: the actual body.
• Function call: runs it: s = add(4, 5);

c#include <stdio.h>
int add(int a, int b);          /* prototype */
int main() {
    printf("%d", add(4, 5));    /* call: prints 9 */
    return 0;
}
int add(int a, int b) {         /* definition */
    return a + b;
}

• Actual arguments are the values in the call; formal arguments are the parameters in the definition.
• In C, arguments are passed by value: the function gets a copy, so changes inside it do not affect the original variable.
• To change the caller's variable, pass its address (call by reference using pointers), as in a swap function.

Recursion is when a function calls itself. Every recursive function needs a base case that stops the recursion and a recursive case that moves towards it.

cint fact(int n) {
    if (n <= 1) return 1;        /* base case */
    return n * fact(n - 1);      /* recursive case */
}

A storage class decides where a variable is stored, its default value, its scope (where it can be used) and its lifetime (how long it exists).