If else Statement in C++
Sometimes we need to execute a block of statements only when a particular condition is met or not met. This is called decision making, as we are executing a certain code after making a decision in the program logic. For decision making in C++, we have four types of control statements (or control structures), which are as follows:
a.if statement
b.nested if statement
c.if-else statement
d.if-else-if statement
If statement in C++
If statement consists a condition, followed by statement or a set of statements as shown below:
if(condition){
Statement(s);
}
The statements inside if parenthesis (usually referred as if body) gets executed only when the given condition is true. If the condition is false then the statements inside if body are completely ignored.
if statement flow diagram
Example of if statement
#include <iostream>
using namespace std;
int main(){
int num=70;
if( num < 100 ){
/* This cout statement will only execute,
* if the above condition is true
*/
cout<<"number is less than 100";
}
if(num > 100){
/* This cout statement will only execute,
* if the above condition is true
*/
cout<<"number is greater than 100";
}
return 0;
}
Output:
number is less than 100
Nested if statement in C++
When there is an if statement inside another if statement then it is called the nested if statement.
if(condition_1)
{
Statement1(s);
if(condition_2) {
Statement2(s);
}
}
Statement1 would execute if the condition_1 is true. Statement2 would only execute if both the conditions( condition_1 and condition_2) are true.
Example of Nested if statement
#include <iostream>
using namespace std;
int main(){
int num=90;
/* Nested if statement. An if statement
* inside another if body
*/
if( num < 100 ){
cout<<"number is less than 100"<<endl;
if(num > 50){
cout<<"number is greater than 50";
}
}
return 0;
}
Output:
number is less than 100
number is greater than 50
If else statement in C++
Sometimes you have a condition and you want to execute a block of code if condition is true and execute another piece of code if the same condition is false. This can be achieved in C++ using if-else statement.
if(condition) {
Statement(s);
}
else {
Statement(s);
}
The statements inside “if” would execute if the condition is true, and the statements inside “else” would execute if the condition is false.
Flow diagram of if-else
Example of if-else statement
#include <iostream>
using namespace std;
int main(){
int num=66;
if( num < 50 ){
//This would run if above condition is true
cout<<"num is less than 50";
}
else {
//This would run if above condition is false
cout<<"num is greater than or equal 50";
}
return 0;
}
Output:
num is greater than or equal 50
if-else-if Statement in C++
if-else-if statement is used when we need to check multiple conditions. In this control structure we have only one “if” and one “else”, however we can have multiple “else if” blocks. This is how it looks:
if(condition_1) {
/*if condition_1 is true execute this*/
statement(s);
}
else if(condition_2) {
/* execute this if condition_1 is not met and
* condition_2 is met
*/
statement(s);
}
else if(condition_3) {
/* execute this if condition_1 & condition_2 are
* not met and condition_3 is met
*/
statement(s);
}
.
.
.
else {
/* if none of the condition is true
* then these statements gets executed
*/
statement(s);
}
Note: The most important point to note here is that in if-else-if, as soon as the condition is met, the corresponding set of statements get executed, rest gets ignored. If none of the condition is met then the statements inside “else” gets executed.
Example of if-else-if
#include <iostream>
using namespace std;
int main(){
int num;
cout<<"Enter an integer number between 1 & 99999: ";
cin>>num;
if(num <100 && num>=1) {
cout<<"Its a two digit number";
}
else if(num <1000 && num>=100) {
cout<<"Its a three digit number";
}
else if(num <10000 && num>=1000) {
cout<<"Its a four digit number";
}
else if(num <100000 && num>=10000) {
cout<<"Its a five digit number";
}
else {
cout<<"number is not between 1 & 99999";
}
return 0;
}
Output:
Enter an integer number between 1 & 99999: 8976
Its a four digit number
Switch Case statement in C++ with example
Switch case statement is used when we have multiple conditions and we need to perform different action based on the condition. When we have multiple conditions and we need to execute a block of statements when a particular condition is satisfied. In such case either we can use lengthy if..else-if statement or switch case. The problem with lengthy if..else-if is that it becomes complex when we have several conditions. The switch case is a clean and efficient method of handling such scenarios.
syntax
switch (variable or an integer expression)
{
case constant:
//C++ code
;
case constant:
//C++ code
;
default:
//C++ code
;
}
Switch Case statement is mostly used with break statement even though the break statement is optional. We will first see an example without break statement and then we will discuss switch case with break
Example of Switch Case
#include <iostream>
using namespace std;
int main(){
int num=5;
switch(num+2) {
case 1:
cout<<"Case1: Value is: "<<num<<endl;
case 2:
cout<<"Case2: Value is: "<<num<<endl;
case 3:
cout<<"Case3: Value is: "<<num<<endl;
default:
cout<<"Default: Value is: "<<num<<endl;
}
return 0;
}
Output:
Default: Value is: 5
Explanation: In switch I gave an expression, you can give variable as well. I gave the expression num+2, where num value is 5 and after addition the expression resulted 7. Since there is no case defined with value 4 the default case got executed.
Switch Case Flow Diagram
It evaluates the value of expression or variable (based on whatever is given inside switch braces), then based on the outcome it executes the corresponding case.
Break statement in Switch Case
Before we discuss about break statement, Let’s see what happens when we don’t use break statement in switch case. See the example below:
#include <iostream>
using namespace std;
int main(){
int i=2;
switch(i) {
case 1: cout<<"Case1 "<<endl;
case 2: cout<<"Case2 "<<endl;
case 3: cout<<"Case3 "<<endl;
case 4: cout<<"Case4 "<<endl;
default: cout<<"Default "<<endl;
}
return 0;
}
Output:
Case2
Case3
Case4
Default
In the above program, we have the variable i inside switch braces, which means whatever the value of variable i is, the corresponding case block gets executed. We have passed integer value 2 to the switch, so the control switched to the case 2, however we don’t have break statement after the case 2 that caused the flow to continue to the subsequent cases till the end. However this is not what we wanted, we wanted to execute the right case block and ignore rest blocks. The solution to this issue is to use the break statement in after every case block.
Break statements are used when you want your program-flow to come out of the switch body. Whenever a break statement is encountered in the switch body, the execution flow would directly come out of the switch, ignoring rest of the cases. This is why you must end each case block with the break statement.
#include <iostream>
using namespace std;
int main(){
int i=2;
switch(i) {
case 1:
cout<<"Case1 "<<endl;
break;
case 2:
cout<<"Case2 "<<endl;
break;
case 3:
cout<<"Case3 "<<endl;
break;
case 4:
cout<<"Case4 "<<endl;
break;
default:
cout<<"Default "<<endl;
}
return 0;
}
Output:
Case2
Now you can see that only case 2 got executed, rest of the subsequent cases were ignored.
Why didn’t I use break statement after default?
The control would itself come out of the switch after default so I didn’t use break statement after it, however if you want you can use it, there is no harm in doing that.
Important Notes
1. Case doesn’t always need to have order 1, 2, 3 and so on. It can have any integer value after case keyword. Also, case doesn’t need to be in an ascending order always, you can specify them in any order based on the requirement.
2. You can also use characters in switch case. for example –
#include <iostream>
using namespace std;
int main(){
char ch='b';
switch(ch) {
case 'd': cout<<"Case1 ";
break;
case 'b': cout<<"Case2 ";
break;
case 'x': cout<<"Case3 ";
break;
case 'y': cout<<"Case4 ";
break;
default: cout<<"Default ";
}
return 0;
}
3. Nesting of switch statements are allowed, which means you can have switch statements inside another switch. However nested switch statements should be avoided as it makes program more complex and less readable.
