Functions in C Programming

 A function is a block of statements that performs a specific task. Let’s say you are writing a C program and you need to perform a same task in that program more than once. 

Lec 5: C if...else Statements all

C if Statement

The syntax of the if statement in C programming is:

if (test expression) 
{
   // statements to be executed if the test expression is true
}

---

How if statement works?

The if statement evaluates the test expression inside the parenthesis ().

• If the test expression is evaluated to true, statements inside the body of if are executed.
• If the test expression is evaluated to false, statements inside the body of if are not executed

Example 1: if statement

// Program to display a number if it is negative

#include <stdio.h>
int main() {
    int number;

    printf("Enter an integer: ");
    scanf("%d", &number);

    // true if number is less than 0
    if (number < 0) {
        printf("You entered %d.\n", number);
    }

    printf("The if statement is easy.");

    return 0;
}

Output 1

Enter an integer: -2
You entered -2.
The if statement is easy.

When the user enters -2, the test expression number<0 is evaluated to true. Hence, You entered -2 is displayed on the screen.

Output 2

Enter an integer: 5
The if statement is easy.

When the user enters 5, the test expression number<0 is evaluated to false and the statement inside the body of if is not executed

---

C if...else Statement

The if statement may have an optional else block. The syntax of the if..else statement is:

if (test expression) {
    // statements to be executed if the test expression is true
}
else {
    // statements to be executed if the test expression is false
}

---

How if...else statement works?

If the test expression is evaluated to true,

• statements inside the body of ifare executed.
• statements inside the body of else are skipped from execution.

If the test expression is evaluated to false,

• statements inside the body of else are executed
• statements inside the body of ifare skipped from execution.

Example 2: if...else statement

// Check whether an integer is odd or even

#include <stdio.h>
int main() {
    int number;
    printf("Enter an integer: ");
    scanf("%d", &number);

    // True if the remainder is 0
    if  (number%2 == 0) {
        printf("%d is an even integer.",number);
    }
    else {
        printf("%d is an odd integer.",number);
    }

    return 0;
}

Output

Enter an integer: 7
7 is an odd integer.

When the user enters 7, the test expression number%2==0 is evaluated to false. Hence, the statement inside the body of else is executed.

C if...else Ladder

The if...else statement executes two different codes depending upon whether the test expression is true or false. Sometimes, a choice has to be made from more than 2 possibilities.

The if...else ladder allows you to check between multiple test expressions and execute different statements.

---

Syntax of if...else Ladder

if (test expression1) {
   // statement(s)
}
else if(test expression2) {
   // statement(s)
}
else if (test expression3) {
   // statement(s)
}
.
.
else {
   // statement(s)
}

---

Nested if...else

It is possible to include an if...elsestatement inside the body of another if...else statement.

---

Example 4: Nested if...else

This program given below relates two integers using either <, > and =similar to the if...else ladder's example. However, we will use a nested if...else statement to solve this problem.

#include <stdio.h>
int main() {
    int number1, number2;
    printf("Enter two integers: ");
    scanf("%d %d", &number1, &number2);

    if (number1 >= number2) {
      if (number1 == number2) {
        printf("Result: %d = %d",number1,number2);
      }
      else {
        printf("Result: %d > %d", number1, number2);
      }
    }
    else {
        printf("Result: %d < %d",number1, number2);
    }

    return 0;
}

If the body of an if...elsestatement has only one statement, you do not need to use brackets {}.

For example, this code

if (a > b) {
    print("Hello");
}
print("Hi");

is equivalent to

if (a > b)
    print("Hello");
print("Hi");