C++ :

#include <bits/stdc++.h>
using namespace std;

//将string转化为int
int num(string s){
	int r = 0;
	int i,t = 1;
	for(i = s.size() - 1;i >= 0;i--){
		r = r + (s[i] - 48) * t;
		t = t * 10;
	}
	
	return r;
} 

//计算结果 
int calc(int a,int b,char c){
	if(c == '+'){
		return a + b;
	}else if(c == '-'){
		return a - b;
	}
}


int main(){
	string s,w;
	int a[1000],i;
	char b[1000];
	
	getline(cin,s);
	w = "";
	int k = 0;
	int x = 0;
	//循环取出每个数和每个运算符 
	for(i = 0;i < s.size();i++){
		if(s[i] >= '0' && s[i] <= '9'){
			w = w + s[i];
			if(i == s.size() - 1 || s[i + 1] == '+' || s[i + 1] == '-'){
				//cout<<w<<endl;
				a[k] = num(w);
				k++;
				w = "";
			}
		}else{
			//cout<<s[i]<<endl;
			b[x] = s[i];
			x++;
		}
	} 
	
	int r = 0;
	r = calc(a[0],a[1],b[0]);
//	cout<<r<<endl;
	for(i = 2;i < k;i++){
//		cout<<r<<" "<<a[i]<<" "<<b[i-1]<<endl;
		r = calc(r,a[i],b[i-1]);
		
	}
	cout<<r<<endl;
}

Python :

a=input()
n=len(a)
s=""
j=0
for i in range(1,n):
    if a[i]=="+" or a[i]=="-":
       s=s+a[j:i]+a[i]
       j=i+1
s=s+a[j:n]       
print(eval(s))