Lecture 4 #

Girish Varma

C Programming Basics #

Focus Topics: #

Operators & Precedence
Conditionals & Loops
Nested Conditionals
Switch Case
Loops (While, For, Do-While)

Operators & Precedence #

Operators are symbols that tell the compiler to perform specific mathematical or logical operations.

Examples:

Arithmetic: +, -, *, /, %
Relational: >, <, >=, <=, ==, !=
Logical: &&, ||, !
Assignment: =, +=, -=, etc.

Operator Precedence Table (Simplified)
From high → low priority:

()
* / %
+ -
< <= > >=
== !=
&&
||
= += -= etc.

Example: Operator Precedence #

#include <stdio.h>
int main() {
    int result = 10 + 20 * 3;
    printf("%d\n", result); // 70 (not 90)
    return 0;
}

Exercise: Operators #

Predict the output without running:

int x = 5, y = 10;
int z = x + y * x / y;
printf("%d\n", z);

Conditionals #

Conditionals control decision-making in programs.

if (condition) {
    // code if condition is true
} else {
    // code if condition is false
}

Nested Conditionals #

if (condition1) {
    if (condition2) {
        // executes if both condition1 and condition2 are true
    } else {
        // executes if condition1 is true, condition2 is false
    }
} else {
    // executes if condition1 is false
}

Example from last class #

if (marks >= 90 && marks <= 100) {
    printf("Grade: A\n");
} else if (marks >= 80) {
    printf("Grade: B\n");
} else if (marks >= 70) {
    printf("Grade: C\n");
} else if (marks >= 60) {
    printf("Grade: D\n");
} else {
    printf("Grade: F\n");
}

Switch Case #

switch (expression) {
    case constant1:
        // code block
        break;
    case constant2:
        // code block
        break;
    ...
    default:
        // default code block
}

Example #

#include <stdio.h>
int main() {
    int day = 3;
    switch (day) {
        case 1: printf("Monday\n"); break;
        case 2: printf("Tuesday\n"); break;
        case 3: printf("Wednesday\n"); break;
        default: printf("Invalid day\n");
    }
    return 0;
}

Loops #

While #

int count = 1;
while (count <= 5) {
    printf("%d\n", count);
    count++; // update
}

Fibonacci #

$f_0 = 0$ $f_1 = 1$ $f_n = f_{n-1} = f_{n-2}$

So $f_2 = 1, f_3 = 2, f_4 = 3, f_5= 5, \cdots$.

Given input $n$, find $f_{n}$.

Fibonacci Program #

int n = 10;
int i = 1;
long long c = 0, f = 0 , t = 1;
while (i < n) {
    c = f + t;
    f = t;
    t = c;
    i = i + 1;
    printf("%d\n", c);
}

Exercise: Euclid’s GCD #

Read Euclid’s GCD Algorithm and implement it using a loop.

Start → Input a, b
        ↓
    a != b?
     /   \
   Yes    No → Print a as GCD → End
   / \
a>b?  No
 /       \
a=a-b   b=b-a

Exercises #

Practice problems for this lecture: L-04 Exercise Questions