Basic string parser

This does not provide argument checking and will only perform operations if all the arguments are one-digit numbers as it only reads 1 character for number arguments. But if you know how to use the string class, this shouldn't be difficult to understand, etc....

Code:

#include <cstdlib>
#include <iostream>
#include <string>
using namespace std;
int main(int argc, char *argv[])
{
    string str1;
    while(true)
    {
               str1.clear();
    cout << "Calc> "; getline(cin,str1);
    if(str1.substr(0,3)=="ADD")
    {
         string temp = str1.substr(4,1);
         int a = atoi(temp.c_str());
         temp.clear();
         temp = str1.substr(6,1);
         int b = atoi(temp.c_str());
         int c = a + b;
         cout << a+b << endl;
    }
    else if(str1.substr(0,3)=="SUB")
    {
       
         string temp = str1.substr(4,1);
         int a = atoi(temp.c_str());
         temp.clear();
         temp = str1.substr(6,1);
         int b = atoi(temp.c_str());
         int c = a - b;
         cout << c << endl;
    }
    else if(str1.substr(0,3)=="MUL")
    {
     
         string temp = str1.substr(4,1);
         int a = atoi(temp.c_str());
         temp.clear();
         temp = str1.substr(6,1);
         int b = atoi(temp.c_str());
         int c = a * b;
         cout << c << endl;
    }
    else if(str1.substr(0,3)=="DIV")
    {
         //note that i'm using float for division, not int
    
         string temp = str1.substr(4,1);
         float a = atoi(temp.c_str());
         temp.clear();
         temp = str1.substr(6,1);
         float b = atoi(temp.c_str());
         float c = a/b;
         cout << c << endl;
    }
    else if(str1.substr(0,3)=="POW")
    {
       
         string temp = str1.substr(4,1);
         int a = atoi(temp.c_str());
         temp.clear();
         temp = str1.substr(6,1);
         int b = atoi(temp.c_str());
         int c = 1;
         if(b>=1)
         {
                 for(int i = 0; i < b; i++)
                 {
                         c*=a;
                 }
         }
         cout << c << endl;
    }
    else if(str1.substr(0,3)=="BYE")
    {
         exit(0);
    }
    else
    {
        cout << "Invalid command, must be ADD, SUB, MUL, DIV, POW or BYE" << endl;
    }
}
    return 0;
}

Example usage:

Code:

Calc> ADD 2 3
5
Calc> SUB 8 3
5
Calc> MUL 2 8
16
Calc> DIV 6 2
3
Calc> POW 2 3
8
Calc> BYE

 

It would be tidier with a switch

 

That wouldn't compile on GCC with a switch statement.

 

Any chance of a C version for me to study?

 

Code:

#include  #include  #include  #include   void getline(char[]); void getsubstr(char[], int, int); void handleop(char[]);  int end = 0;  int main() {     while (1) {         printf(&quot;%s&quot;, &quot;CALC> &quot;);         char[] line;         getline(line);         handleop(line);         if (end) {             break;         }     }     return 0; }   void getline(char[] buf) {     int c;     int idx = 0;     while ((c = getchar()) != '\n') {         buf[idx++] = c;     } }  void getsubstr(char[] buf, char[] src, int off, int len) {     assert(strlen(buf) >= off && strlen(buf) >= off + len && strlen(buf) >= len);     memcpy(buf, src + off, off + len); }  void handleop(char[] line) {     assert(strlen(line) >= 7);     char[] op;     getsubstr(line, 0, 3);     char[][2] rawnums;     getsubstr(rawnums[0], 4, 1);     getsubstr(rawnums[1], 6, 1);     int[] nums;     /* DANGER: atoi WILL RETURN 0 IF NON INTEGER */     nums[0] = atoi(rawnums[0]);     nums[1] = atoi(rawnums[1]);     if (!strcmp(op, &quot;ADD&quot;)) {         printf(&quot;%d&quot;, nums[0] + nums[1]);     } else if (!strcmp(op, &quot;MUL&quot;)) {         printf(&quot;%d&quot;, nums[0] * nums[1]);     } else if (!strcmp(op, &quot;DIV&quot;)) {         if (!nums[1]) {             fprintf(stderr, &quot;%s&quot;, &quot;cannot divide by 0!&quot;);             return;         }         float a = nums[0];         float b = nums[1];         printf(&quot;%d&quot;, (a / b));     } else if (!strcmp(op, &quot;POW&quot;)) {         int result = -123;         if (nums[0] == 1) {             result = 1;         } else if (nums[1] == 1) {             result = nums[0];         } else if (!nums[0] || !nums[1]) {             result = 0;         }         if (result == -123) {             result = 1;             for (int i = 0; i < nums[1]; ++i) {                 result *= result;             }         }         printf(&quot;%d&quot;, result);     } else if (!strcmp(op, &quot;BYE&quot;)) {         end = 1;     } else {         printf(&quot;%s&quot;, &quot;Invalid operation. Only ADD, SUB, MUL, DIV, POW, and BYE are supported.&quot;);     }     printf(&quot;%c&quot;, '\n'); }

written by me.

 

Newlines and indentation are your friend

 

Ignorant. This forum has a faggotry text parsing system, that temoved my includes and my indentation.

 

Try pastebin.ca?

 

If you don't want to use non-standard and legacy functions such as atoi, you can use std::stringstream for parsing and converting.

std::stringstream ss("Hello 123");
std::string str;
int n;
ss >> str >> n;

std::cout << str << " " << n; // Would print "Hello 123"

Or, if you have boost, boost::lexical_cast.

 

Ah, nice find. Never knew of that before.

 

You could of done it like this,

Code:

   if(!memcmp(str1.c_str(),"ADD ",4))
    {
        int num1,num2;
        sscanf(str1.c_str(),"ADD %d %d",&num1,&num2);
        cout << num1+num2;
    }