how to restart a for loop from first iteration if a condition work.. in this code i want to return to first iteration of for loop after the if condition true and display the error

fs=input('Enter the sampling Freq=');
tstart=input('Enter start time=');
tend=input('Enter end time=');
NB=input('Enter number of breakpoints=');
t(1)=tstart; t(NB+2)=tend;
for i=2:NB+1
    t(i)=input(sprintf('Enter the position of break point %d=',i-1));
if (t(i)<tstart || t(i)>tend)
        disp('Erorr!!.. Enter the position of break points within the range of time');   
   end
end

Answer 1

[KALYAN ACHARJYA]

for i=1:iterations_number
    %do your finding
  if condition true
     i=1; %assign i value again 1 (initial), first iteration
  end
end

Your case

fs=input('Enter the sampling Freq=');
tstart=input('Enter start time=');
tend=input('Enter end time=');
NB=input('Enter number of breakpoints=');
t(1)=tstart; t(NB+2)=tend;
for i=2:NB+1
    t(i)=input(sprintf('Enter the position of break point %d=',i-1));
if (t(i)<tstart || t(i)>tend)
        disp('Erorr!!.. Enter the position of break points within the range of time');
        i=2;
   end
end

[Alaa Nagy]

the same problem, for loop return to secod iteration and so on , i want to return to ( Enter the position of break point 1) all times when i enter it not within time range

Enter number of breakpoints=2

Enter the position of break point 1=-5

Erorr!!.. Enter the position of break points within the range of time

Enter the position of break point 2

[KALYAN ACHARJYA]

If you just change the iterations number, wheather first or second, the results will be same, have you change any data within the loop in different iterations?

Your code, results of loop statments are depend on i only, and i start from 2, which I am considering the first iterations.

[Alaa Nagy]

i modifiy code as u say and run it again, the problem is the same , the total code is here

fs=input('Enter the sampling Freq=');
tstart=input('Enter start time=');
tend=input('Enter end time=');
NB=input('Enter number of breakpoints=');
t(1)=tstart; t(NB+2)=tend;
for i=2:NB+1
    t(i)=input(sprintf('Enter the position of break point %d=',i-1));
   if (t(i)<tstart || t(i)>tend)
        disp('Erorr!!.. Enter the position of break points within the range of time');
       i=2;    
   end
   
end
for n=1:NB+1     
    tln =linspace(t(n),t(n+1),(t(n+1)-t(n))*fs+1);
    ytype=menu('select the signal','Impulse','Dc','Ramp','exponential','sinusoidal');
     if ytype==1
        Area=input('Enter the area of the impulse=');
        timpulse=input('Enter the moment of the impulse=');
        p=(timpulse-t(n))*fs+1; %the impulse point number in the vector
        yn=zeros(1,length(tln));
        yn(1,p)=Area;
    elseif ytype==2
        Amp=input('Enter the amplitude of the Dc=');
        yn =Amp*ones(1,length(tln));
    elseif ytype==3
        slope=input('Enter the slope of the ramp=');
        intercept=input('Enter the intercept of the ramp=');
        yn =slope*tln+intercept;
    elseif ytype==4
        Amp=input('Enter the amplitude of exponential=');
        exponent=input('Enter the exponent =');
        yn =Amp*exp(exponent*tln);
    else
        Amp=input('Enter the amplitude of the sin=');
        freq=input('Enter the freq of the sin=');
        phase=input('Enter the phase=');
        offset=input('Enter the offset=');
        yn =offset+Amp*sin(2*pi*freq*tln+ phase);
    
    end
    if n==1
        t1=tln;
        y=yn;   
    else 
    t1=[t1 tln];
    y=[y yn];
    end
end
plot(t1,y)

[KALYAN ACHARJYA]

Hello Nagy, you are doing simple mistake, when the first for loop meets the certain condition, you display the following error message

disp('Erorr!!.. Enter the position of break points within the range of time');

After, I supposed you have to asked the t range again, then only its works, otherwise tstart and tend are same, on that case just changeing loop doesnot helps.

My point are>>

1. If the condition is true, ask to reenter the following statement again

tstart=input('Enter start time=');
tend=input('Enter end time=');

2. restart the loop again, when the first loop doesnot meets the condition with respective tstart and tend, then only it move towards for loop 2.

Clarify? Reply first please, as I am goint to sleep

[KALYAN ACHARJYA]

I have little edited, its pass to the 2nd loop

clc;
clear all;
close all;
fs=input('Enter the sampling Freq=');
tstart=input('Enter start time=');
tend=input('Enter end time=');
NB=input('Enter number of breakpoints=');
t(1)=tstart; t(NB+2)=tend;
for i=2:NB+1
    t(i)=input(sprintf('Enter the position of break point %d=',i-1));
   if (t(i)<tstart || t(i)>tend)
        disp('Erorr!!.. Enter the position of break points within the range of time');
        tstart=input('Enter start time=');
        tend=input('Enter end time=');
        i=2;    
   end
end
for n=1:NB+1     
    tln =linspace(t(n),t(n+1),(t(n+1)-t(n))*fs+1);
    ytype=menu('select the signal','Impulse','Dc','Ramp','exponential','sinusoidal');
     if ytype==1
        Area=input('Enter the area of the impulse=');
        timpulse=input('Enter the moment of the impulse=');
        p=(timpulse-t(n))*fs+1; %the impulse point number in the vector
        yn=zeros(1,length(tln));
        yn(1,p)=Area;
    elseif ytype==2
        Amp=input('Enter the amplitude of the Dc=');
        yn =Amp*ones(1,length(tln));
    elseif ytype==3
        slope=input('Enter the slope of the ramp=');
        intercept=input('Enter the intercept of the ramp=');
        yn =slope*tln+intercept;
    elseif ytype==4
        Amp=input('Enter the amplitude of exponential=');
        exponent=input('Enter the exponent =');
  yn =Amp*exp(exponent*tln);
    else
        Amp=input('Enter the amplitude of the sin=');
        freq=input('Enter the freq of the sin=');
        phase=input('Enter the phase=');
        offset=input('Enter the offset=');
        yn =offset+Amp*sin(2*pi*freq*tln+ phase);
    
    end
    if n==1
        t1=tln;
        y=yn;   
    else 
    t1=[t1 tln];
    y=[y yn];
    end
end
plot(t1,y)

[KALYAN ACHARJYA]

Hope this Helps!

Good Night!

[Alaa Nagy]

thanks for your help but i find a way to do what i need without your change in code using while loop instead for loop

[KALYAN ACHARJYA]

ok, you can do that.

[Image Analyst]

Note that if you change the loop iterator value inside the loop, it takes effect only until the bottom of the loop. When the loop starts the next iteration, it will have the same value it would have had, had you not changed it. It will not start at the next number after the number you changed it to. So if you do

for k = 1 : 100
    k = 30;
end

so that on the very first iteration k gets set to 30, the second iteration will start with k=2, not with k=31.

It's not recommended to ever change the loop variable because of this high possibility of being confusing/deceptive/unexpected.

[KALYAN ACHARJYA]

Agreed @ImageAnalyst Sir, thanks for great explanation.