Hello,

I am using this code found on TI-Calc to solve equations and inequalities 

It works very well... excepted that it always ends on an error NO SIGN CHNG, which means that the solve command cannot found another solution.

:ClrHome
:Input Str1
:For(I,1,length(Str1
:sub(Str1,I,1→Str0
:If inString("=≠>≥<≤",Str0
:Then
:I→A
:length(Str1→I
:End
:End
:sub(Str1,1,A-1→Y1
:sub(Str1,A+1,length(Str1)-A→Y2
:"Y1-Y2→Y3
:solve(Y3,X,1,{‾300,300→A
:nDeriv(Y3,X,A+E‾3→E
:Output(4,3,A
:4→I
:Disp "
:Goto 4
:Lbl 1
:solve(Y3/(X-A),X,{‾2,2},{‾E3,E3→B
:nDeriv(Y3,X,B+E‾3→E
:Output(5,3,B
:Goto 4
:Lbl 2
:solve(Y3/(X-A)/(X-B),X,{‾E2,E2},{‾E3,E3→C
:nDeriv(Y3,X,C+E‾3→E
:Output(6,3,C
:Goto 4
:Lbl 3
:solve(Y3/(X-A)/(X-B)/(X-C),X,0,{‾E3,E3→D
:nDeriv(Y3,X,D+E‾3→E
:Output(7,3,D
:Lbl 4
:Disp "
:Output(I,1,"X
:Output(I,2,"=
:If Str0="≠
:Output(I,2,"≠
:If Str0=">" or Str0="<
:Then
:Output(I,2,">
:If E<0 and Str0=">" or E>0 and Str0="<
:Output(I,2,"<
:End
:If Str0="≥" or Str0="≤
:Then
:Output(I,2,"≥
:If E<0 and Str0="≥" or E>0 and Str0="≤
:Output(I,2,"≤
:End
:I+1→I
:If I=5
:Goto 1
:If I=6
:Goto 2
:If I=7
:Goto 3
:Pause
:"
When you study how this program works, you can see that it always searches for 4 solutions to any equation, and gives the error if there is less than 4 solutions...

To prevent the error, is there any mean to know how many solutions the equation have  ?
If I could know it at the begining of the program, I could forbid it to search for more solutions... and give errors.

Thank you for your help...

yes, obviously.

Thank you anyway, but no

We should reproduce this feature on a z80...