Introduction of the decision-making statement

In C programming, decision-making statements are used to make choices based on certain conditions. These statements allow a program to take different actions depending on the outcome of a condition (true or false). This is an essential part of writing logical and interactive programs. Here are the main types of decision-making statements in C:

1. if Statement: 

An if statement is a conditional control structure used in programming to execute a block of code only if a specified condition is true. It helps make decisions in a program. 

Syntax:

if (condition) {
// Code to execute if the condition is true
}

Example in C:

int age = 18;
if (age >= 18) {
printf("You are eligible to vote.");
}

#include<stdio.h>
#include<conio.h>
int main() {
int number;
// Ask the user to enter an integer number
printf("Enter an integer number:");
scanf("%d", &number);
// Check if the number is negative
if (number < 0) {
printf("The number is negative.\n");
}
else{
printf("The given number is positive.")
}
return 0;
}

2. Nested If Statement:

A nested if statement is an if statement inside another if statement. It allows you to make decisions within other decisions. This is useful when you need to check multiple conditions, one inside another.

Syntax:

if(condition){
if(condition){
//body
}
}

Flow chart of nested if statement

#include<stdio.h>
int main() {
int age = 70;
if (age >= 18) {
printf("You are eligible to vote.\n");
if (age >= 60) {
printf("You are also a senior citizen.\n");
}
}
return 0;
}

Write a C program to check if a student has passed an exam and if they are eligible for a scholarship.

• A student passes if their marks are greater than or equal to 40.
• A student is eligible for a scholarship only if they pass and their marks are greater than or equal to 90.

#include <stdio.h>
int main() {
int marks;
// Ask user for marks
printf("Enter your marks: ");
scanf("%d", &marks);
if (marks >= 40) {
printf("You have passed the exam.\n");
if (marks >= 90) {
printf("Congratulations! You are eligible for a scholarship.\n");
}
}
return 0;
}

3. if-else statement :

The A if-elsestatement in C is used to execute one block of code if a condition is true, and another block of code if the condition is false. It helps you make informed decisions in your program.

syntax

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

Write a program to read a number from the user and determine whether the number is even or odd.

#include<stdio.h>
int main() {
int number;
printf("Enter a number: ");
scanf("%d", &number);
if (number % 2 == 0) {
printf("The number is even.\n");
} else {
printf("The number is odd.\n");
}
return 0;
}

4. Nested if-else Statement: 

A nested if-else statement means using one if or else if or else block inside anotheriforelseblock. It is helpful to test multiple conditions in a structured manner.

Syntax of Nested if-else in C

if (condition1) {
if(condition2)
{
statement-1;
}
else{
statement-2;
}
}
else {
if(condition3){
statement-3;
}
else
{
statement-4;
}
}

Flowchart of nested if-else statement

Write a program to read three numbers from the user and determine the largest number among them.

#include <stdio.h>
int main() {
int num1, num2, num3;
// Input from user
printf("Enter first number: ");
scanf("%d", &num1);
printf("Enter second number: ");
scanf("%d", &num2);
printf("Enter third number: ");
scanf("%d", &num3);
// Nested if-else to find the largest
if (num1 >= num2) {
if (num1 >= num3) {
printf("The largest number is: %d\n", num1);
} else {
printf("The largest number is: %d\n", num3);
}
} else {
if (num2 >= num3) {
printf("The largest number is: %d\n", num2);
} else {
printf("The largest number is: %d\n", num3);
}
}
return 0;
}

Switch Statement in C

The switch statement in C is a type of decision-making statement that allows a variable to be tested for equality against multiple constant values. Each value is called a case, and the variable is checked against each case. It is often used as a cleaner alternative to using multiple if .. else…if  statements.

syntax:

switch (expression) {
case constant1:
// code to execute if expression == constant1
break;
case constant2:
// code to execute if expression == constant2
break;
// you can have any number of cases
default:
// code to execute if no case matches
}

Write a C program to print the day of the week based on user input (1 to 7). Use a switch statement.

#include <stdio.h>
int main() {
int day;
printf("Enter day number (1 to 7): ");
scanf("%d", &day);
switch (day) {
case 1:
printf("Sunday");
break;
case 2:
printf("Monday");
break;
case 3:
printf("Tuesday");
break;
case 4:
printf("Wednesday");
break;
case 5:
printf("Thursday");
break;
case 6:
printf("Friday");
break;
case 7:
printf("Saturday");
break;
default:
printf("Invalid day number");
}
return 0;
}

Write a C program to perform a basic calculator using a switch statement.

#include <stdio.h>
int main() {
char operator;
float num1, num2;
printf("Enter an operator (+, -, *, /): ");
scanf(" %c", &operator);
printf("Enter two numbers: ");
scanf("%f %f", &num1, &num2);
switch (operator) {
case '+':
printf("Result = %.2f", num1 + num2);
break;
case '-':
printf("Result = %.2f", num1 - num2);
break;
case '*':
printf("Result = %.2f", num1 * num2);
break;
case '/':
if (num2 != 0)
printf("Result = %.2f", num1 / num2);
else
printf("Division by zero is not allowed.");
break;
default:
printf("Invalid operator.");
}
return 0;
}

Write a C program to check whether a character is a vowel or a consonant using the switch statement.

#include <stdio.h>
int main() {
char ch;
printf("Enter a character: ");
scanf(" %c", &ch);
switch (ch) {
case 'a':
case 'e':
case 'i':
case 'o':
case 'u':
case 'A':
case 'E':
case 'I':
case 'O':
case 'U':
printf("Vowel");
break;
default:
printf("Consonant");
}
return 0;
}

Loop Statements in Programming

Loop statements are used to execute a block of code repeatedly as long as a certain condition is true. They help reduce redundancy and make code efficient.

Types of Loop Statements

Entry control loop: An Entry Controlled Loop is a type of loop where the condition is checked before the execution of the loop body. If the condition is false at the beginning, the loop does not run even once. Examples of entry-controlled loops are For and While loops.

for Loop

• A for loop is an entry-controlled loop used to execute a block of code repeatedly for a known number of times. It is commonly used when the number of iterations is fixed. The syntax of the for loop is 

for(initialization; condition; increment/decrement) {
// Code to be executed
}

Initialization means setting the starting value of the loop counter, and conditional means the loop runs as long as this condition is met, and increments/decrements means changes the loop counter after each iteration

The flow chart for a for loop is shown in the diagram below.

Example: Print numbers from 1 to 5 by using a for loop

#include <stdio.h>
int main() {
int i;
for(i = 1; i <= 5; i++) {
printf("%d ", i);
}
return 0;
}
Out Put of program:
1 2 3 4 5

While loop:

A while loop in C is an entry-controlled loop that repeatedly executes a block of code as long as a given condition is true. The condition is checked before the loop body runs. Syntax of while loop:

while (condition) {
// Code to be executed repeatedly
}

Example: Print numbers from 1 to 5 using a while loop

#include <stdio.h>
int main() {
int i = 1;
while (i <= 5) {
printf("%d\n", i);
i++;
}
return 0;
}

Exit Controlled Loop: An Exit Controlled Loop is a type of loop where the condition is checked after the execution of the loop body. So, the loop executes at least once, even if the condition is false at the beginning.

do…while Loop in C: A do-while loop is an exit-controlled loop in C programming. This means that the loop body will execute at least once, and then the condition is checked. If the condition is true, the loop continues; otherwise, it stops.

syntax

do {
// Statements to execute
} while (condition);

The flow chart of do while loop is shown in the diagram below.

Comparison between for loop and the while loop