Decision Making in C (if , if..else, Nested if, if-else-if )

In C, programs can choose which part of the code to execute based on some condition. This ability is called decision making and the statements used for it are called conditional statements. These statements evaluate one or more conditions and make the decision whether to execute a block of code or not.

For example, consider that there is a show that starts only when certain number of people are present in the audience. So, you can write a program like as shown:

#include <stdio.h>

int main() {

    // Number of people in the audience
    int num = 100;
    
    // Conditional code inside decision making statement
    if (num > 50) {
        printf("Start the show");
    }

    return 0;
}

Start the show

In the above program, the show only starts when the number of people is greater than 50. It is specified in the if statement (a type of conditional statement) as a condition (num > 50). You can decrease the value of num to less than 50 and try rerunning the code.

Types of Conditional Statements in C

In the above program, we have used if statement, but there are many different types of conditional statements available in C language:

1. if in C

The if statement is the simplest decision-making statement. It is used to decide whether a certain statement or block of statements will be executed or not i.e if a certain condition is true then a block of statements is executed otherwise not.

A condition is any expression that evaluates to either a true or false (or values convertible to true or flase).

Example

#include <stdio.h>

int main() {
    
    int i = 10;

    // If statement
    if (i < 18) {
        printf("Eligible for vote");
    }
}

Eligible for vote

The expression inside () parenthesis is the condition and set of statements inside {} braces is its body. If the condition is true, only then the body will be executed.

If there is only a single statement in the body, {} braces can be omitted.

2. if-else in C

The ifstatement alone tells us that if a condition is true, it will execute a block of statements and if the condition is false, it won’t. But what if we want to do something else when the condition is false? Here comes the C elsestatement. We can use the elsestatement with the ifstatement to execute a block of code when the condition is false. The if-else statement consists of two blocks, one for false expression and one for true expression.

Example

#include <stdio.h>

int main() {
    int i = 10;

    if (i > 18) {
        printf("Eligible for vote");
    }
    else {
        printf("Not Eligible for vote");
    }
    return 0;
}

Not Eligible for vote

The block of code following the else statement is executed as the condition present in the if statement is false.

3. Nested if-else in C

A nested if in C is an if statement that is the target of another if statement. Nested if statements mean an if statement inside another if statement. Yes, C allow us to nested if statements within if statements, i.e, we can place an if statement inside another if statement.

Example

#include <stdio.h>

int main(){
    int i = 10;

    if (i == 10) {
        if (i < 18)
            printf("Still not eligible for vote");
        else
            printf("Eligible for vote\n");
    }
    else {
        if (i == 20) {
            if (i < 22)
                printf("i is smaller than 22 too\n");
            else
                printf("i is greater than 25");
        }
    }

    return 0;
}

Still not eligible for vote

4. if-else-if Ladder in C

The if else if statements are used when the user has to decide among multiple options. The C if statements are executed from the top down. As soon as one of the conditions controlling the if is true, the statement associated with that if is executed, and the rest of the C else-if ladder is bypassed. If none of the conditions is true, then the final else statement will be executed. if-else-if ladder is similar to the switch statement.

Example

#include <stdio.h>

int main() {
    int i = 20;

    // If else ladder with three conditions
    if (i == 10)
        printf("Not Eligible");
    else if (i == 15)
        printf("wait for three years");
    else if (i == 20)
        printf("You can vote");
    else
        printf("Not a valid age");
        
    return 0;
}

You can vote

5. switch Statement in C

The switch case statement is an alternative to the if else if ladder that can be used to execute the conditional code based on the value of the variable specified in the switch statement. The switch block consists of cases to be executed based on the value of the switch variable.

Example

#include <stdio.h>

int main() {
    
    // variable to be used in switch statement
    int var = 18;

    // declaring switch cases
    switch (var) {
    case 15:
        printf("You are a kid");
        break;
    case 18:
        printf("Eligible for vote");
        break;
    default:
        printf("Default Case is executed");
        break;
    }

    return 0;
}

Eligible for vote

Note: The switch expression should evaluate to either integer or character. It cannot evaluate any other data type.

6. Conditional Operator in C

The conditional operator is used to add conditional code in our program. It is similar to the if-else statement. It is also known as the ternary operator as it works on three operands.

Example:

#include <stdio.h>

int main() {
    int var;
    int flag = 0;

    // using conditional operator to assign the value to var
    // according to the value of flag
    var = flag == 0 ? 25 : -25;
    printf("Value of var when flag is 0: %d\n", var);

    return 0;
}

Value of var when flag is 0: 25

7. Jump Statements in C

These statements are used in C for the unconditional flow of control throughout the functions in a program. They support four types of jump statements:

A) break

This loop control statement is used to terminate the loop. As soon as the break statement is encountered from within a loop, the loop iterations stop there, and control returns from the loop immediately to the first statement after the loop.

Example

#include <stdio.h>

int main() {
    int arr[] = { 1, 2, 3, 4, 5, 6 };
    int key = 3;
    int size = 6;

    for (int i = 0; i < size; i++) {
        if (arr[i] == key) {
            printf("Element found at position: %d",
                   (i + 1));
            break;
        }
    }

    return 0;
}

Element found at position: 3

B) continue

This loop control statement is just like the break statement. The continue statement is opposite to that of the break statement, instead of terminating the loop, it forces to execute the next iteration of the loop. 
As the name suggests the continue statement forces the loop to continue or execute the next iteration. When the continue statement is executed in the loop, the code inside the loop following the continue statement will be skipped and the next iteration of the loop will begin.

Example:

#include <stdio.h>

int main() {
    for (int i = 1; i <= 10; i++) {

        // If i is equals to 6,
        // continue to next iteration
        // without printing
        if (i == 6)
            continue;
        else
            printf("%d ", i);
    }

    return 0;
}

1 2 3 4 5 7 8 9 10 

C) goto 

The goto statement in C also referred to as the unconditional jump statement can be used to jump from one point to another within a function.

Examples:

#include <stdio.h>

int main() {
    int n = 1;
label:
    printf("%d ", n);
    n++;
    if (n <= 10)
        goto label;
    return 0;
}

1 2 3 4 5 6 7 8 9 10 

D) return

The return in C returns the flow of the execution to the function from where it is called. This statement does not mandatorily need any conditional statements. As soon as the statement is executed, the flow of the program stops immediately and returns the control from where it was called. The return statement may or may not return anything for a void function, but for a non-void function, a return value must be returned.

Example:

#include <stdio.h>
int SUM(int a, int b) {
    int s1 = a + b;
    return s1;
}

int main()
{
    int num1 = 10;
    int num2 = 10;
    int sum_of = SUM(num1, num2);
    printf("%d", sum_of);
    return 0;
}

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Article Tags :

• C Language
• C++
• C Basics
• CPP-Basics
• CBSE - Class 11
• CPP-Control-Flow
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