1427. Calculator

The student Vasya has a younger brother, Peter, who went to the first grade and began learning arithmetic. For homework in the first grade, he was assigned numerous problems involving addition and subtraction. Peter asked Vasya to check his homework. Upon seeing the two-page scribbled tests, Vasya was horrified by the workload and decided to teach Peter to use a computer for self-checking. To accomplish this, Vasya needs to write a program that computes the answers to the required arithmetic problems.

Input. One line contains numbers and symbols ‘+’ and ‘-’. The length of the line does not exceed 10000 characters, and the values of all numbers are not greater than 10000.

Output. Print one integer – the result of the calculation.

Sample input	Sample output
1+22-3+4-5+123	142

SOLUTION

strings

Algorithm analysis

Read the first term into the variable res. Next, split the remaining line into pairs: an operator symbol and a term.

Sequentially read the pairs (character, number) until the end of the file, performing the corresponding operations.

Algorithm implementation

Read the first term into the variable res.

scanf("%d",&res);

Read the operation sign ch (addition or subtraction), followed by an integer x. Add x to or subtract it from the total result res.

while (scanf("%c%d", &ch, &x) == 2)

if (ch == '+') res += x; else res -= x;

Print the result of the computations.

printf("%d\n",res);

Algorithm implementation – iostream

Read the first term into the variable res.

cin >> res;

Continue the loop until the next character is not the end-of-line character ‘\n’. The peek function returns the next character from the input stream without extracting it.

while(cin.peek() != '\n')

{

Read the operation sign ch (addition or subtraction), followed by an integer x. Add x to or subtract it from the total result res.

cin >> ch >> x;

if (ch == '+') res += x; else res -= x;

}

Print the result of the computations.

cout << res << endl;

Java implementation

import java.util.*;

public class Main

{

public static void main(String[] args)

{

Scanner con = new Scanner(System.in);

String s = con.nextLine();

StringTokenizer st1 = new StringTokenizer(s, "+-");

StringTokenizer st2 = new StringTokenizer(s, "0123456789");

int res = Integer.parseInt(st1.nextToken());

while (st1.hasMoreTokens())

{

int x = Integer.parseInt(st1.nextToken());

if (st2.nextToken().equals("+")) res += x;

else res -= x;

}

System.out.println(res);

con.close();

}

}

Python implementation

Compute the value of the input expression and print the result.

· The eval() function evaluates a string as a Python expression and returns the result.

print(eval(input()))