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POEvaluate a Math Expression given in string form without using API
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copied!<p>I want to evaluate an expression like <code>-4-12-2*12-3-4*5</code> given in a <code>String</code> form <strong>without using API</strong> as I am a beginner and want to grasp the logic.</p> <p>Given below is my unsuccessful attempt to this problem which, if you may like, ignore and suggest appropriate logic.And of course your codes are also welcome :-)</p> <pre><code>public class SolveExpression3 { static String testcase1 = "-4-12-2*12-3-4*5"; public static void main(String args[]){ SolveExpression3 testInstance= new SolveExpression3(); int result = testInstance.solve(testcase1); System.out.println("Result is : "+result); } public int solve(String str){ int sum = 1; int num1 = 0; int num2 = 0; String num = ""; int len = str.length(); System.out.println(str); for (int i = len-1 ; i >= 0; i--) { char ch = str.charAt(i); if(ch == '*') { String s = ""; num1 = num2 = 0; //to get the number on left of * for (int j = i; j >= 0; j--) { char c = str.charAt(j); if(c == '+' || c == '-' || j == 1) { num1 = stringToInt(s); s = ""; break; } else { s = c + s; } } //to get the number on right of * for (int j = i; j <= len; j++) { char c = str.charAt(j); if(c == '+' || c == '-' || j == len-1) { num2 = stringToInt(s); s = ""; break; } else { s = c + s; } } sum = sum + num1*num2; } else { num = ch + num; } } len = str.length(); for (int i = len-1; i >= 0; i--) { char ch = str.charAt(i); if(ch==' ') {} else if(ch=='+') { sum = sum + stringToInt(num); num = ""; } else if(ch=='-') { sum = sum - stringToInt(num); num = ""; } else { num = ch + num; } } return sum; } public int stringToInt(String str) { int number=0; for(int i = 0; i < str.length(); i++) { int num = str.charAt(i) - 48; number = number*10+num; } return number; } } </code></pre>

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