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Summary on the if statement in C

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The if statement is the basic conditional structure and is found in all programming languages. It allows you to execute different blocks of code according to a condition. It is the basis of many algorithms and allows a computer to make a choice based on the data sent to it.

Syntax of the if statement

The if statement takes, as input, a condition in the form of a boolean variable and executes a block of instructions if it is true (in this case we say that the condition is fulfilled) and another if it is false.

  if(condition){
    <liste d'instructions si condition=true>;
  }else{
    <liste d'instructions si condition=false>;
  }

Example of a code determining the sign of a variable with the if statement:

int val=-10;

void setup() {
  Serial.begin(9600);
}

void loop() {
  if(val>=0){
    Serial.println(F("Value is positive"));
  }else{
    Serial.println(F("Value is negative"));
  }
  val=val+2; //increment val
  if(val>10) val=-10; // set val to initial value
  delay(500); //delay for monitor display
}

A boolean is a type of variable equal to true( 1-true) or false(0-false). In the C(Arduino) language, boolean variables are initialized using the keyword bool or boolean. A boolean can be obtained in different ways

 condition = variable == 10;    // variable égale à 10? 
 condition = temperature>30;   // temperature est supérieure à 30 
 condition = vitesse <= 100    // vitesse inférieure ou égale à 100 
 condition = !true // condition égale  non vraie (faux) 
   
bool test(int val){
  //retourne vraie si la valeur est supérieur à 200
  return val>200;
}
condition=(temperature>30) && (vitesse<20);

Other syntaxes

The if statement can have several syntaxes depending on the case.

It is possible to forget the braces when the only instruction is on one line.

  if(condition) <instructions>;

Example:

if(condtion) Serial.println("Conditon est réalisée");

If there is no instruction to execute when the condition is not fulfilled, it is possible to forget the else{} block.

  if(condition){
    <liste d'instructions>;
  }

If several conditions are evaluated at the same time

  if(condition){
   // <liste d'instructions si condition==true>;
  }else if(condition2){
    //<liste d'instructions si condition==false && condition2==true>;
  }else if(condition3){
    //<liste d'instructions si condition==false && condition2==false && condition3==true>;
  }else{
    //<liste d'instructions si aucune condition réalisée>;
  }

Things to remember

Bonus

In simple cases, it is possible to use the « ? » statement with the following syntax

resultat = (condition) ? <instruction si vraie> : <instruction si faux>

Example, line of code that returns the sign of a variable:

 
  int signe= (variable>=0) ? 1:-1; // retourne 1 si la valeur est positive et - 1 si elle est négative

Make sure you understand booleans and logical operators to use the if statement correctly. Once you have mastered this statement, your algorithms will be able to make good decisions.

Sources

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