If condition not working as expected

Question

In the last condition in else if (see code marked with ***), I am not getting my screen with the laser/specklke fail, if both failflag 1 and failgflag 5 is there, however it shows me laser fail instead. Please help to solve my error.

#include <UTFT.h>
#include <avr/pgmspace.h>
#include <SPI.h>
#include <avr/wdt.h>
extern uint8_t Retro8x16[];
extern unsigned int virtek3[]; //display pic
UTFT myDisplay(ST7735, 11, 13, 3, 2, 4);
int buttonhold = 0;
int state = HIGH;
int tim = 0;
int tim1 = 0;
int tim2 = 0;
int button = 1;
float volt = 0;
float volt1 = 0;
float volt2 = 0;
float volt3 = 0;
float volt4 = 0;
float volt5 = 0;
float volt6 = 0;
float volt7 = 0;
float volt8 = 0;
float volt9 = 0;
float volt10 = 0;
float volt11 = 0;
float volt12 = 0;
float volt13 = 0;
float volt14 = 0;
float volt15 = 0;
float volt16 = 0;
float volt17 = 0;
float volt18 = 0;
float volt19 = 0;
float volt20 = 0;
float volt21 = 0;
float vcc = 0.0;
float temp = 0.0;
float r1 = 10000.0;
float r2 = 2200.0;
int failflag = 0;
//void(* resetFunc) (void) = 0;
void setup()
{
 pinMode(18, INPUT); //For NEXT button
 pinMode(20, OUTPUT); //For Relay power
 pinMode(21, OUTPUT); //For Relay power
 pinMode(14, INPUT);
 Serial.begin(9600);
 myDisplay.InitLCD();
 myDisplay.clrScr();
 myDisplay.setFont(Retro8x16);
 digitalWrite(20, HIGH);
 digitalWrite(20, HIGH);
 digitalWrite(21, LOW);
 attachInterrupt(digitalPinToInterrupt(18), next, LOW);
 myDisplay.fillScr(255, 255, 255);
 myDisplay.drawBitmap(20, 1, 126, 126, virtek3, 1);
 while (1) {
 delay(100);
 if (state == LOW) {
 break;
 }
 } 
}
void next() {
 state = LOW;
 Serial.println(buttonhold);
 buttonhold++;
 if (buttonhold > 500) {
 //digitalWrite(21, LOW);
 resetFunc(); 
 }
 }
void loop()
{
 digitalWrite(20, LOW);
 digitalWrite(21, LOW); //Relay is ON.
 myDisplay.clrScr();
 state = HIGH;
 buttonhold = 0;
 while (1) {
 failflag = 0;
 float voltage_value = 0;
 myDisplay.setColor(0, 255, 255);
 myDisplay.print("1.Voltage Test", 35, 0);
 myDisplay.setColor(255, 255, 255);
 myDisplay.print("(V)", 0, 20);
 myDisplay.print("LASER",50,20);
 myDisplay.print("SPECKLE",100,20);
delay(1000);
 //FOR ANALOG A4 PIN
 //A4 pin connected to TP2 of speckle
 float volt_b = 0;
 float volt_c = 0;
 float volt_d = 0;
 for (int i = 0; i < 1000; i++) {
 volt_b =(volt_b + (4.99 / 1024 * analogRead(A4))); 
 }
 volt_b = volt_b / 1000;
 volt1 = volt_b / (r2 / (r1 + r2));
 myDisplay.setColor(255, 255, 255);
 myDisplay.print("TP2 :", 0, 38); 
 myDisplay.setColor(0, 255, 255);
 myDisplay.print("NA", 60, 37);
 Serial.println(volt1); //ANALOG A4
 if (volt1 >= 5 && volt1 <= 7.30) {
 myDisplay.setColor(0, 255, 0);
 myDisplay.printNumF(volt1, 2, 120, 38);
 //myDisplay.print(" ", 130, 20);
 } else { 
 myDisplay.setColor(0, 0, 255);
 myDisplay.printNumF(volt1, 2, 120, 38);
 //myDisplay.print(" ", 150, 38);
 failflag = 1;
 }
 delay(2000);
 digitalWrite(20, HIGH);
 digitalWrite(21, LOW);
 delay(2000);
 //FOR ANALOG A4 PIN
 //A4 pin connected to TP2/L of SPECKLE
 for (int i = 0; i < 1000; i++) {
 volt_b =(volt_b + (4.99 / 1024 * analogRead(A4))); 
 }
 volt_b = volt_b / 1000;
 volt2 = volt_b / (r2 / (r1 + r2));
 myDisplay.setColor(255, 255, 255);
 myDisplay.print("TP2/L :", 0, 56);
 myDisplay.setColor(0, 255, 255);
 myDisplay.print("NA", 60, 56);
 Serial.println(volt2); //ANALOG A4
 if (volt2 >= 5 && volt2 <= 0.05) {
 myDisplay.setColor(0, 255, 0);
 myDisplay.printNumF(volt2, 2, 120, 56);
 //myDisplay.print(" ", 130, 20);
 } else { 
 myDisplay.setColor(0, 0, 255);
 myDisplay.printNumF(volt2, 2, 120, 56);
 //myDisplay.print(" ", 150, 56);
 failflag = 1;
 }
 //FOR ANALOG A1 PIN
 //A1 pin connected to J1_1 of SENSOR
 volt = analogRead(A1);
 volt3 =(volt * 4.8) /1024;
 myDisplay.setColor(255, 255, 255);
 myDisplay.print("J1_1 :", 0, 74);
 Serial.println(volt3); //ANALOG A1
 if (volt3 >= 0 && volt3 <= 5.25) {
 myDisplay.setColor(0, 255, 0);
 myDisplay.printNumF(volt3, 2, 60, 74);
 //myDisplay.print(" ", 130, 20);
 } else { 
 myDisplay.setColor(0, 0, 255);
 myDisplay.printNumF(volt3, 2, 60, 74);
 //myDisplay.print(" ", 150, 74);
 failflag = 5;
 }
 myDisplay.setColor(0, 255, 255);
 myDisplay.print("NA", 125, 74);
 //FOR ANALOG A0 PIN
 //A0 pin connected to J2_2 of SENSOR
 for (int i = 0; i < 1000; i++) {
 volt_b =(volt_b + (4.99 / 1024 * analogRead(A0))); 
 }
 volt_b = volt_b / 1000;
 volt4 = volt_b / (r2 / (r1 + r2));
 //volt4 = volt_c - 2.7;
 myDisplay.setColor(255, 255, 255);
 myDisplay.print("J2_2 :", 0, 92);
 Serial.println(volt4); //ANALOG A0
 if (volt4 >= 5 && volt4 <= 8.82) {
 myDisplay.setColor(0, 255, 0);
 myDisplay.printNumF(volt4, 2, 60, 92);
 //myDisplay.print(" ", 130, 20);
 } else {
 myDisplay.setColor(0, 0, 255);
 myDisplay.printNumF(volt4, 2, 60, 92);
 //myDisplay.print(" ", 150, 92);
 failflag = 5;
 }
 myDisplay.setColor(0, 255, 255);
 myDisplay.print("NA", 125, 93);
 digitalWrite(20, LOW);
 digitalWrite(20, LOW);
 delay(2000);
 if (failflag == 5) {
 myDisplay.setColor(0, 0, 255);
 myDisplay.print("LASER FAIL", 35, 108);
 delay(4000);
 state = 0;
 }
 else if (failflag == 1) {
 myDisplay.setColor(0, 0, 255);
 myDisplay.print("SPECKLE FAIL", 35, 108);
 delay(40000);
 state = 0;
 }
 // *** Here the condition not working START
 else if ((failflag == 5) && (failflag == 1)) {
 myDisplay.setColor(0, 0, 255);
 myDisplay.print("LASER/SPECKLE FAIL", 15, 108);
 delay(40000);
 state = 0;
 }
 // *** Here the condition not working END

• jsotola: what is the program supposed to do? .... what are you expecting to happen? .... what actually happens? .... do you get any errors?

Answer 1

(failflag == 5) && (failflag == 1))

failflag can't be both 5 and 1 at the same time.

Answer 2

As you ask for two different assignments for the same var its never gone to work this way. Two quick options:
Do binary addidition

 failflag = 0;
 if(errorA) failflag += 1;
 if(errorB) failflag += 2;
 if(errorC) failflag += 4;
 if(errorD) failflag += 8;
//then you can decode combined errors as follows
else if (failflag == 13) {
 Serial.println("Errors: A, C, D"); // 1 + 4 + 8 =13
}

The other quick one is defining failflag as bool array

bool failflag [5] = {00000}; // 5 elements
 if(errorA) failflag [0]= 1;
 if(errorB) failflag [1]= 1;
 if(errorC) failflag [2]= 1;
 if(errorD) failflag [3]= 1;
//then you can decode combined errors as follows
else if ( failflag [0] == 1 && failflag [2]== 1 && failflag [3]== 1) {
 Serial.println("Errors: A, C, D"); // 1 + 4 + 8 =13
}

as we have failflag[i] as a bool we can condense the code to

else if ( failflag [0] && failflag [2] && failflag [3]) {
 Serial.println("Errors: A, C, D"); // 1 + 4 + 8 =13
}

Whatever suits your needs. As I said just 2 quick ones
Edit Cleaning up you question other things to change:
Get rid of the delay() (except in setup to initialize your hardware and in loop during debuging.

The 21 float vars could be stores in a float array

 float myFloatVars [22]

and write the values to the position

 myFloatVars [11] = myMeasureFunction();

you can do this even in a timed for loop doing a recurring FIFO function (kind of circle buffer), the first saved value is dumped if the array is full to put the next one in. So you are able to produce a "gliding" average, which is what you want

• jsotola: bool data type is true/false, so the test is if ( failflag [0]) or if ( !failflag [0]) .... if ( failflag [0]== 1) equates to if ( true==true), which is redundant
• Codebreaker007: Your right copy & paste error. changed it to true so that the OP sees whats going on - the redundancy helps beginners to understand. Thanks for the eagle eye
• jsotola: note: null termination is used for strings, not for numerical arrays
• jsotola: this is for OP's benefit .... if(errorA) failflag [0]= 1; can be replaced by failflag[0] = errorA, but only if the failflag[0] is not set by multiple sources
• paxhi: Thank you so much . I use bool array and it works. Really appreciate you legend !