String to int example

Author: PhysicsX

Cpp/stringToInt.cpp

@@ -0,0 +1,55 @@
+#include <string>
+#include <iostream>
+#include <climits>
+
+int stringToInteger(const std::string& str)
+{
+    int result = 0;
+    bool isNegative = false;
+    int i = 0;
+
+    //check str is negative or not
+    if(str[0] == '-')
+    {
+        isNegative = true;
+        i++;
+    }
+
+    for(; i<str.size(); ++i)
+    {
+        if(std::isdigit(str[i]))
+        {
+
+            // to check the overflow is exist or not
+            // if INT_MAX > (result * 10 + (str[i] - '0')) then there is a overflow
+            // if(result * 10 + (str[i] - '0') > INT_MAX) // but this will not work
+            // because result * 10 + (str[i] - '0') if result is cause overflow then there
+            // will be undefined behaviour so it is good idea to compare it with result
+
+            if(result > (INT_MAX - (str[i] - '0')) / 10)
+            {
+                std::cout<<"overflow detected"<<std::endl;
+                return isNegative ? INT_MIN : INT_MAX;
+            }
+
+            result = result * 10 + (str[i] - '0');
+        }
+        else
+            return 0;
+    }
+
+    if(isNegative)
+        result = -result;
+
+    return result;
+}
+
+int main()
+{
+    std::cout<<stringToInteger("123")<<std::endl;
+    std::cout<<stringToInteger("99999999999999999999999999");
+
+    std::endl(std::cout);
+
+    return 0;
+}