Evaluate Reverse Polish Notation (String-type convertion)

Question

Evaluate the value of an arithmetic expression in Reverse Polish Notation.
Valid operators is +,-, *,/. Each operand is an integer or another expression.
Some Examples:
["2", "1", "+", "3", "*"], ((2 + 1) * 3), 9
["4", "+", "5", "/", "+"], (4 + (13/5)), 6

1ST TRY

classSolution { Public:    intEVALRPN (vector<string> &tokens) {        intOperant1; intOperant2; stringstr; intret; BOOLFirstop =false;  for(inti =0; I < tokens.size (); i++) {str=Tokens[i]; if(!firstop) {Operant1=getInt (str);; Firstop=true; }            Else if(str = ="+") {ret= Operant1 +Operant2; }            Else if(str = ="-") {ret= Operant1-Operant2; }            Else if(str = ="*") {ret= Operant1 *Operant2; }            Else if(str = ="/") {ret= OPERANT1/Operant2; }            Else{Operant2=getInt (str); Firstop=false; }        }                returnret; }    intGetInt (stringstr) {        intRET =0;  for(inti =0; I < str.length (); i++) {ret= ret*Ten+Str[i]; }        returnret; }};

2ND TRY

Consider a situation where there is only one operand

classSolution { Public:    intEVALRPN (vector<string> &tokens) {        intOperant1; intOperant2; stringstr; intret; BOOLFirstop =false;  for(inti =0; I < tokens.size (); i++) {str=Tokens[i]; if(!firstop) {Operant1=getInt (str); Firstop=true; }            Else if(str = ="+") {Operant1+=Operant2; }            Else if(str = ="-") {Operant1-=Operant2; }            Else if(str = ="*") {Operant1*=Operant2; }            Else if(str = ="/") {Operant1/=Operant2; }            Else{Operant2=getInt (str); }        }        returnOperant1; }        intGetInt (stringstr) {        intRET =0;  for(inti =0; I < str.length (); i++) {ret= ret*Ten+ (str[i]-'0'); }        returnret; }};

Result:wrong

Input: ["3", "4", "+"]
Output: 23
Expected:-1

3RD TRY

Consider the case of negative numbers

classSolution { Public:    intEVALRPN (vector<string> &tokens) {        intOperant1; intOperant2; intret; stringstr; Stack<int>Operantstack;  for(inti =0; I < tokens.size (); i++) {str=Tokens[i]; if(str = ="+") {Operant2=Operantstack.top ();                Operantstack.pop (); Operant1=Operantstack.top ();                Operantstack.pop (); Operantstack.push (Operant1+Operant2); }            Else if(str = ="-") {Operant2=Operantstack.top ();                Operantstack.pop (); Operant1=Operantstack.top ();                Operantstack.pop (); Operantstack.push (Operant1-Operant2); }            Else if(str = ="*") {Operant2=Operantstack.top ();                Operantstack.pop (); Operant1=Operantstack.top ();                Operantstack.pop (); Operantstack.push (Operant1*Operant2); }            Else if(str = ="/") {Operant2=Operantstack.top ();                Operantstack.pop (); Operant1=Operantstack.top ();                Operantstack.pop (); Operantstack.push (Operant1/Operant2); }            Else{operantstack.push (getInt (str)); }        }        returnOperantstack.top (); }        intGetInt (stringstr) {        intRET =0; BOOLNegflag =false;  for(inti =0; I < str.length (); i++)        {            if(str[i]=='-') Negflag =true; Else if(negflag) {ret= ret*Ten-(str[i]-'0'); }            Else{ret= ret*Ten+ (str[i]-'0'); }        }        returnret; }};

result:accepted

4TH TRY

Convert a string to an int using the built-in function atoi

classSolution { Public:    intEVALRPN (vector<string> &tokens) {Stack<int>Operandstack; intOperand1; intOperand2;  for(inti =0; I < tokens.size (); i++){            if(tokens[i]=="+") {Operand1=Operandstack.top ();                Operandstack.pop (); Operand2=Operandstack.top ();                Operandstack.pop (); Operand2+=Operand1;            Operandstack.push (OPERAND2); }            Else if(tokens[i]=="-") {Operand1=Operandstack.top ();                Operandstack.pop (); Operand2=Operandstack.top ();                Operandstack.pop (); Operand2-=Operand1;            Operandstack.push (OPERAND2); }            Else if(tokens[i]=="*") {Operand1=Operandstack.top ();                Operandstack.pop (); Operand2=Operandstack.top ();                Operandstack.pop (); Operand2*=Operand1;            Operandstack.push (OPERAND2); }            Else if(tokens[i]=="/") {Operand1=Operandstack.top ();                Operandstack.pop (); Operand2=Operandstack.top ();                Operandstack.pop (); Operand2/=Operand1;            Operandstack.push (OPERAND2); }            Else{operand1=atoi (Tokens[i].c_str ());            Operandstack.push (OPERAND1); }        }        returnOperandstack.top (); }};

result:accepted

Evaluate Reverse Polish Notation (String-type convertion)