C Exercises: Reads an expression and evaluates

C Basic Declarations and Expressions: Exercise-150 with Solution

Write a C program that reads an expression and evaluates it.

Terms and conditions:
The expression consists of numerical values, operators and parentheses, and the ends with '='.
The operators includes +, -, *, / where, represents, addition, subtraction, multiplication and division.
When two operators have the same precedence, they are applied to left to right.
You may assume that there is no division by zero.
All calculation is performed as integers, and after the decimal point should be truncated
Length of the expression will not exceed 100.
-1 × 10 9 <= intermediate results of computation <= 10 9
Sample Input:
4
10-2*3=
8*(8+2-5)=

Sample Solution:

C Code:

#include <stdio.h>
#include<string.h>

int addsub();
int muldiv();
int term();

char input[101];
int pos = 0;

int term(){
  int n = 0;

  if(input[pos] == '('){
    pos++;
    n = addsub();
    
    if(input[pos] == ')'){
      pos++;
      return n;
    }
  }else{
    while('0' <= input[pos] && input[pos] <= '9'){
      n = n*10 + (input[pos] - '0');
      pos++;
    }
  }
  return n;
}

int muldiv(){
  int first,second;
  
  first = term();
  for(;;){
    if(input[pos] == '*'){
      pos++;
      second = term();
      first *= second; 
    }else if(input[pos] == '/'){
      pos++;
      second = term();
      first /= second;
    }else{
      return first;
    }
  }
}

int addsub(){
  int first,second;
  
  first = muldiv();
  
  for(;;){
    if(input[pos] == '+'){
      pos++;
      second = muldiv();
      first += second; 
    }else if(input[pos] == '-'){
      pos++;
      second = muldiv();
      first -= second;
    }else{
      return first;
    }
  }
  
}

int main(){
  int n,i,j;
  printf("Input an expression using +, -, *, / operators:\n");
  scanf("%s",input);
  printf("%d\n",addsub());  
  return 0;
  }

Sample Output:

Input an expression using +, -, *, / operators:
1+6*8-4/2
47

Sample Output:

Input an expression using +, -, *, / operators:
25/5-6*7+2
-35

Sample Output:

Input an expression using +, -, *, / operators:
9+6+(5*2)-5
20

Flowchart:

C programming Code Editor:

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