Add Calculate code for integers

cpp/.vscode/settings.json

@@ -0,0 +1,5 @@
+{
+    "files.associations": {
+        "iostream": "cpp"
+    }
+}

cpp/calc.cpp

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+#include <iostream>
+#include<cstdlib>
+#include<cstring>
+
+static int pos = 0;
+int calc_expression_value(const char * expression);
+
+int calc_factor_value(const char * factor){
+    int result = 0;
+    char c = factor[pos];
+    if( c == '('){          // if expression has '(', calculate the expression in the '()'
+        pos++;
+        result = calc_expression_value(factor);
+        pos++;
+    }else{
+        while(isdigit(c)){  // Get the number to calculate
+            result = 10 * result + c - '0';
+            pos++;
+            c = factor[pos];
+        }
+    }
+    return result;
+}
+
+int calc_term_value(const char * term){
+    int result = calc_factor_value(term);   // Get the first number
+    while(true){
+        //pos++;    // Calc the multiplication and divide
+        char op = term[pos];
+        if(op == '*' || op == '/'){
+            pos++;
+            int value = calc_factor_value(term);    // Get another value
+            if(op == '*') result *= value;
+            else result /= value;
+        }else{
+            break;
+        }
+    }
+    return result;
+}
+
+int calc_expression_value(const char * expression){
+    int result = calc_term_value(expression);   // Calc the result of expression
+    //bool more = true;
+    while(true){
+        char op = expression[pos];
+        if(op == '+' || op == '-'){         // Calculate for add and subb
+            pos++;
+            int value = calc_term_value(expression);
+            if( op == '+') result += value;
+            else result -= value;
+        }else{
+            break;
+        }
+    }
+    return result;
+}
+
+int main(int argc,char ** argv){
+    char expression[1000];
+    std::cin.getline(expression,sizeof(expression));
+    std::cout<<calc_expression_value(expression)<<std::endl;
+    return 0;
+}