Simple calculator C++ loop [closed] - c++

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I am a student in my first year.
Could someone help me with an assignment?
Simple calc C++
In the first line the number of tests n. In the next n lines operations Each operation contains the operation type (+ *) the number of k numbers to be processed, and k numbers
Output
Result
Example
Input
3
+ 3 3.1 5.2 -8.3
* 2 1 3.3
+ 1 3
Output
0
3.3
3
My code
int n, k;
char x;
cin >> n;
int tab[100];
for (int i = 0; i < n; i++)
{
cin >> x >> k;
for (int j = 0; j < k; j++)
{
cin >> tab[j];
if (x == '+')
{
tab[j] += tab[j + 1];
}
if (x == '*')
{
tab[j] *= tab[j + 1];
}
cout << tab[j];
}
}
return 0;
}

Answer 1

There are a few problems.
your tab is of type int so it can only store integers e.g.: 1,2,3,4,5 not floating point numbers like 1.3 2.5 3.3, you should consider changing tab to be of type float.
your loop logic and indexing is totally wrong, and you are accessing the wrong elements, you should have some sort of accumulator variable that will accumulate the results instead of storing them in an array. e.g.:
float accumulator = 0;
cin >> input_number;
accumulator += input_number;`
the best advice i can give you is to learn to use the debugger, the debugger is your friend, you should use it to walk through your code, line by line and understand what each lines does to each variable, and read the contents of each variable, i cannot recommend a certain source for learning to use a debugger as it depends on your IDE, but you should maybe check a video on using debugger with IDE X, it can be a good start for learning to use an IDE GUI.

Answer 2

The issues are many. Just some:
The purpose of tab is unclear. You do not need to store the operands, you can accumulate a result in a single value.
In any event tab[j + 1]; is not initialised at point of use.
If you want to output the results after all the input as indicated in the question then you do need somewhere to store the results for later output.
You do need to output the results.
The input and output types do need to be a floating-point type.
Greater clarity of thought might arise if you were to use clear variable names that reflected their purpose and perhaps some comments. If you have to explain what the code does (even to yourself) often you spot the errors. A good technique is to write the comments first, to explain what you need to code rather than explaining the code you have written and assume erroneously to be correct. Also you need to get out of that "all variables at the top" habit.
Example:
#include <iostream>
int main()
{
// Get number of calculations
int ncalc = 0 ;
std::cin >> ncalc ;
// Create array for results
double* result = new double[ncalc] ;
// For each calculation
for( int calc = 0; calc < ncalc; calc++ )
{
// Get the operator
char op = 0 ;
std::cin >> op ;
// Get the number of operands
int noperands = 0 ;
std::cin >> noperands ;
// Get initial operand in accumulator
double accumulator = 0 ;
std::cin >> accumulator ;
// For each remaining operand...
for( int i = 1; i < noperands; i++)
{
// Get the operand
double operand = 0 ;
std::cin >> operand ;
// Perform the operation
switch( op )
{
// For +, accumulate sum
case '+' : accumulator += operand ; break ;
// For * accumulate product
case '*' : accumulator *= operand ; break ;
}
}
// Store accumulated result
result[calc] = accumulator ;
}
// Output results
for( int calc = 0; calc < ncalc; calc++ )
{
std::cout << result[calc] << '\n' ;
}
delete[] result ;
return 0;
}