Extract integer from string - c++

Question

I am new to C++ strings and vectors and would like to know what the issue with this code is, I was provided a vector input of strings in the form "a/b+c/d" and had to print a vector in "e/f" for where a, b, c, d are integers and e/f is in the reduced fraction form. Please help as I want to learn concept of strings properly and shift to C++ from C
vector< string > reducedFractionSums(vector < string > expressions) { int a[4]={0,0,0,0}; vector < string > results;
vector < string > results;
for(int i=0;i<expressions.size();i++){
int tmp=0;
int count=0;
for(int j=0;j<expressions[i].length();j++){
if(isdigit(expressions[i][j])){
tmp=expressions[i][j];
tmp=tmp-48;
a[count]=a[count]*10 + tmp;
}
else
count++;
}
int min=a[0];
for(int i=1;i<4;i++){
if(a[i]<min){
min=a[i];
}
}
int e,f,g=1; //g for GreatestCommonDivisor
f=a[1]*a[3];
e=(a[0]*a[3])+(a[2]*a[1]);
for(int i=1;i<=min;i++){
if(e%i==0 && f%i==0){
g=i;
}
}
e=e/g;
f=f/g;
results.push_back(e + "/" + f);
}
return results;
}
int main(){
vector < string > input;
vector < string > output;
int t;
cin>>t;
while(t--){
string s;
cin>>s;
input.push_back(s);
}
output=reducedFractionSums(input);
for(int i = 0;i<output.size();i++){
cout<<output.at(i);
}
return 1;
}

Answer 1

Use std::stoi to convert Single integer from string, std::to_string to convert integer to string and __gcd to calculate GCD which is defined in algorithm header file to find reduced form of fraction.
#include <bits/stdc++.h>
using namespace std;
vector<int>reduced_fraction(vector<int>v) // Function to find reduced fraction form
{
int num = v[0]*v[3]+v[1]*v[2]; // numerator = a*d+b*c
int den = v[1]*v[3]; // denominator = b*d
int gcd = __gcd(num,den); // gcd = gcd(greatest common divisor) of numerator and denominator
num/=gcd; // num/den = e/f(reduced fraction)
den/=gcd;
vector<int>frac;
frac.push_back(num);
frac.push_back(den);
return frac;
}
int main() {
string s,st;
vector<string>fr; // vector to store strings of form a/b+c/d
int n=2; //Number of Strings
for(int i=0;i<n;i++)
{
cin>>s;
fr.push_back(s);
}
for(int i=0;i<n;i++)
{
s=fr[i];
vector <int>v,red_frac;
while(s.compare("")!=0)
{
if(s.at(0)=='/' || s.at(0)=='+')
s.erase(0,1);
else
{
st=to_string(stoi(s)); // fetch integer from string
v.push_back(stoi(s));
s=s.erase(0,st.length()); // remove integer from string
}
}
red_frac=reduced_fraction(v); // red_frac->reduced fraction
cout<<red_frac[0]<<"/"<<red_frac[1]<<endl;
}
return 0;
}
Input:
14/2+9/6
8/4+5/4
Output:
17/2
13/4
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