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

There come situations in real life when we need to make some decisions and based on these decisions, we decide what should we do next. Similar situations arise in programming also where we need to make some decisions and based on these decisions we will execute the next block of code.

Decision making statements in programming languages decides the direction of flow of program execution. Decision making statements available in C++ are:

  1. if statement
  2. if..else statements
  3. nested if statements
  4. if-else-if ladder
  5. switch statements
  6. Jump Statements:

if statement



if statement is the most simple 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 statement is executed otherwise not.
Syntax:

if(condition) 
{
   // Statements to execute if
   // condition is true
}

Here, condition after evaluation will be either true or false. if statement accepts boolean values – if the value is true then it will execute the block of statements below it otherwise not.
If we do not provide the curly braces ‘{‘ and ‘}’ after if( condition ) then by default if statement will consider the first immediately below statement to be inside its block.
Example:

if(condition)
   statement1;
   statement2;

// Here if the condition is true, if block 
// will consider only statement1 to be inside 
// its block.

Flowchart:
if-statement-in-java

C

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// C program to illustrate If statement
#include <stdio.h>
  
int main() {
    int i = 10;
  
    if (i > 15)
    {
       printf("10 is less than 15");
    }    
     
    printf("I am Not in if");
}

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C++

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// C++ program to illustrate If statement
#include<iostream>
using namespace std;
  
    int main()
    {
        int i = 10;
   
        if (i > 15)
        {
           cout<<"10 is less than 15";
        }    
         
        cout<<"I am Not in if";
    }

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Output:

I am Not in if

As the condition present in the if statement is false. So, the block below the if statement is not executed.

if- else

The if statement 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 if the condition is false. Here comes the else statement. We can use the else statement with if statement to execute a block of code when the condition is false.
Syntax:

if (condition)
{
    // Executes this block if
    // condition is true
}
else
{
    // Executes this block if
    // condition is false
}

Flowchart:
if-else-statement
Example:

C

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// C program to illustrate If statement
#include <stdio.h>
  
int main() {
    int i = 20;
  
    if (i < 15)
        printf("i is smaller than 15");
    else
        printf("i is greater than 15");
              
    return 0;    
}

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C++

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// C++ program to illustrate if-else statement
#include<iostream>
using namespace std;
  
int main()
 {
        int i = 20;
   
        if (i < 15)
            cout<<"i is smaller than 15";
        else
            cout<<"i is greater than 15";
              
    return 0;    
 }

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Output:

i is greater than 15

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


nested-if

A nested if is an if statement that is the target of another if statement. Nested if statements means an if statement inside another if statement. Yes, C++ allows us to nest if statements within if statements. i.e, we can place an if statement inside another if statement.
Syntax:

if (condition1) 
{
   // Executes when condition1 is true
   if (condition2) 
   {
      // Executes when condition2 is true
   }
}

Flowchart:
nested-if
Example:

C

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// C program to illustrate nested-if statement
#include <stdio.h>
  
int main() {
    int i = 10;
  
    if (i == 10)
    {
        // First if statement
        if (i < 15)
           printf("i is smaller than 15\n");
  
        // Nested - if statement
        // Will only be executed if statement above
        // is true
        if (i < 12)
            printf("i is smaller than 12 too\n");
        else
            printf("i is greater than 15");
    }
  
    return 0;
}

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C++

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// C++ program to illustrate nested-if statement
#include <iostream>
using namespace std;
  
int main() 
{
    int i = 10;
  
    if (i == 10)
    {
        // First if statement
        if (i < 15)
           cout<<"i is smaller than 15\n";
  
        // Nested - if statement
        // Will only be executed if statement above
        // is true
        if (i < 12)
            cout<<"i is smaller than 12 too\n";
        else
            cout<<"i is greater than 15";
    }
  
    return 0;
}

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Output:

i is smaller than 15
i is smaller than 12 too

if-else-if ladder

Here, a user can decide among multiple options. The 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 ladder is bypassed. If none of the conditions is true, then the final else statement will be executed.
Syntax:

if (condition)
    statement;
else if (condition)
    statement;
.
.
else
    statement;

if-else-if-ladder
Example:

C

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// C program to illustrate nested-if statement
#include <stdio.h>
  
int main() {
    int i = 20;
   
    if (i == 10)
        printf("i is 10");
    else if (i == 15)
        printf("i is 15");
    else if (i == 20)
        printf("i is 20");
    else
        printf("i is not present");
}

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C++

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// C++ program to illustrate if-else-if ladder
#include<iostream>
using namespace std;
  
int main()
{
    int i = 20;
   
    if (i == 10)
        cout<<"i is 10";
    else if (i == 15)
        cout<<"i is 15";
    else if (i == 20)
        cout<<"i is 20";
    else
        cout<<"i is not present";
}

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Output:

i is 20

Jump Statement

These statements are used in C++ for unconditional flow of control through out the funtions in a program. C++ supports four type of jump statements:


  1. 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 stops there and control returns from the loop immediately to the first statement after the loop.
    Syntax:

    break;
    

    Basically break statements are used in the situations when we are not sure about the actual number of iterations for the loop or we want to terminate the loop based on some condition.

    Example:

    C

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    // C program to illustrate 
    // Linear Search 
      
    #include <stdio.h>
      
    void findElement(int arr[], int size, int key) 
        // loop to traverse array and search for key 
        for (int i = 0; i < size; i++) { 
            if (arr[i] == key) { 
                printf("Element found at position: %d", (i + 1)); 
            
        
      
    int main() {
        int arr[] = { 1, 2, 3, 4, 5, 6 }; 
          
        // no of elements
        int n = 6;  
          
        // key to be searched 
        int key = 3; 
      
        // Calling function to find the key 
        findElement(arr, n, key); 
      
        return 0;
    }

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    C++

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    // CPP program to illustrate
    // Linear Search
    #include <iostream>
    using namespace std;
      
    void findElement(int arr[], int size, int key)
    {
        // loop to traverse array and search for key
        for (int i = 0; i < size; i++) {
            if (arr[i] == key) {
                cout << "Element found at position: " << (i + 1);
            }
        }
    }
      
    // Driver program to test above function
    int main()
    {
        int arr[] = { 1, 2, 3, 4, 5, 6 };
        int n = 6; // no of elements
        int key = 3; // key to be searched
      
        // Calling function to find the key
        findElement(arr, n, key);
      
        return 0;
    }

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    Output:

    Element found at position: 3
    
  2. continue: This loop control statement is just like the break statement. continue statement is opposite to that of break statement, instead of terminating the loop, it forces to execute the next iteration of the loop.
    As the name suggest 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 next iteration of the loop will begin.
    Syntax:

    continue;
    


    Example:

    C

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    // C program to explain the use 
    // of continue statement 
    #include <stdio.h>
      
    int main() {
        // loop from 1 to 10 
        for (int i = 1; i <= 10; i++) { 
      
            // If i is equals to 6, 
            // continue to next iteration 
            // without printing 
            if (i == 6) 
                continue
      
            else
                // otherwise print the value of i 
                printf("%d ", i); 
        
      
        return 0; 
    }

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    C++

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    // C++ program to explain the use
    // of continue statement
      
    #include <iostream>
    using namespace std;
      
    int main()
    {
        // loop from 1 to 10
        for (int i = 1; i <= 10; i++) {
      
            // If i is equals to 6,
            // continue to next iteration
            // without printing
            if (i == 6)
                continue;
      
            else
                // otherwise print the value of i
                cout << i << " ";
        }
      
        return 0;
    }

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    Output:

    1 2 3 4 5 7 8 9 10
    
  3. goto: The goto statement is a jump statement which is sometimes also referred to as unconditional jump statement. The goto statement can be used to jump from anywhere to anywhere within a function.
    Syntax:

    Syntax1      |   Syntax2
    ----------------------------
    goto label;  |    label:  
    .            |    .
    .            |    .
    .            |    .
    label:       |    goto label;
    

    In the above syntax, the first line tells the compiler to go to or jump to the statement marked as a label. Here label is a user-defined identifier which indicates the target statement. The statement immediately followed after ‘label:’ is the destination statement. The ‘label:’ can also appear before the ‘goto label;’ statement in the above syntax.
    goto
    Below are some examples on how to use goto statement:
    Examples:

    C

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    // C program to print numbers
    // from 1 to 10 using goto statement
    #include <stdio.h>
      
    // function to print numbers from 1 to 10
    void printNumbers()
    {
        int n = 1;
    label:
        printf("%d ",n);
        n++;
        if (n <= 10)
            goto label;
    }
      
    // Driver program to test above function
    int main() {
        printNumbers();
        return 0;
    }

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    C++

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    // C++ program to print numbers
    // from 1 to 10 using goto statement
    #include <iostream>
    using namespace std;
      
    // function to print numbers from 1 to 10
    void printNumbers()
    {
        int n = 1;
    label:
        cout << n << " ";
        n++;
        if (n <= 10)
            goto label;
    }
      
    // Driver program to test above function
    int main()
    {
        printNumbers();
        return 0;
    }

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    Output:

    1 2 3 4 5 6 7 8 9 10
    
  4. return: This statement 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 return 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 is must be returned.
    Syntax:

    return[expression];

    Example:

    C

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    // C code to illustrate return
    // statement
    #include <stdio.h> 
      
    // non-void return type
    // function to calculate sum
    int SUM(int a, int b) 
        int s1 = a + b;
        return s1; 
      
    // returns void
    // function to print
    void Print(int s2)
    {
        printf("The sum is %d", s2);
        return;
    }
      
    int main() 
        int num1 = 10;
        int num2 = 10;
        int sum_of = SUM(num1, num2);
        Print(sum_of);
        return 0;
    }

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    C++

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    // C++ code to illustrate return
    // statement
    #include <iostream>
    using namespace std;
      
    // non-void return type
    // function to calculate sum
    int SUM(int a, int b) 
        int s1 = a + b;
        return s1; 
      
    // returns void
    // function to print
    void Print(int s2)
    {
        cout << "The sum is "<< s2;
        return;
    }
      
    int main() 
        int num1 = 10;
        int num2 = 10;
        int sum_of = SUM(num1, num2);
        Print(sum_of);
        return 0;
    }

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    Output:

    The sum is 20
    
This article is contributed by Harsh Agarwal. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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