Inverse matrix

[DaNguyen]

Hi everyone,
I wrote the code to inverse matrix. However, the result have some problems.
How to solute the problems?
Thank u too much

#include<iostream>
#include<cstdio>
#include<string>
#include<cmath>
#include<fstream>
#include<ostream>

using namespace std;

int nhapmatran(float, int);
int xuatmatran(float, int);
float dinhthuc(float, int);
float nghichdao(float, int);

int nhapmatran(float a[100][100], int n)
{
	int i,j;
	for (i=0; i<n; i++){
	    for (j=0; j<n; j++){
		cin>>a[i][j];
	    }
	}
}

int xuatmatran(float a[100][100], int n)
{	
	int i,j;
	
	for (i=0; i<n; i++){
		cout<<endl;
	    for (j=0; j<n; j++){
		cout<<a[i][j]<<"\t";
	    }
	}
}

float dinhthuc(float a[100][100], int n)
{	
	float b[100];
	float c[100];
	int i,j,k,kt, dem=0;
	float h;
	float dt=1;

		for (i=0; i<n-1; i++){
		if(a[i][i]==0){
			kt =0;
		for (j=0;j<n;j++){
			if(a[i][j]!=0){
				for(k=0;k<n;k++){
					c[k] = a[k][i];
					a[k][i]=a[k][j];
					a[k][j]=c[k];
				}
			dem++;
			kt++;
			break;
			}
		}
		}
		if(kt==0) return 0;
		b[i]=a[i][i];
		
	for (j=0; j<n; j++) a[i][j]/=b[i];
	for (j=i+1; j<n; j++){
		h = a[j][i];
	for (k=0;k<n;k++) a[j][k]=a[j][k]-h*a[i][k];
	}
	}

	b[n-1]=a[n-1][n-1];
		for(i=0; i<n; i++)
			dt*=b[i];
			//cout<<kq<<endl;
	if (dem%2==0) return dt;
	else return -dt;
	//xuatmatran(a,n);
}

float nghichdao(float a[100][100], int n)
{
	
	float ratio,t,k;
	int i,j,l;

	k = dinhthuc(a,n);
	

    for(i = 0; i < n; i++){
        for(j = n; j < 2*n; j++){
            if(j==(i+n))
                a[i][j] = 1.0;
            else
                a[i][j] = 0.0;
        }
    }

    for (i=0; i<n; i++){
	if (a[i-1][1]<a[i][1])
	for (j=1; j<=2*n; j++){
		ratio=a[i][j];
		a[i][j]=a[i][j];
		a[i][j]=ratio;
	}
    }
    for(i = 0; i < n; i++){
        for(j = 0; j < n; j++){
            if(i!=j){
                ratio = a[j][i]/a[i][i];
                for(l = 0; l < 2*n; l++){
                    a[j][l] -= a[i][l]*ratio;
                }
            }
        }
    }
    for(i = 0; i < n; i++){
        ratio = a[i][i];
        for(j = 0; j < 2*n; j++){
            a[i][j] /=ratio;
        }
    }
  
    for(i = 0; i < n; i++){
	  // cout<<endl;
        for(j = n; j < 2*n; j++){
            cout<< a[i][j];
            cout<<"\t";
        }
	cout<<endl;
    }
	return 0;
	//else cout<<"ERROR!"<<endl;
}
	
int main()
{	
	float a[100][100];
	float b[100][100];
	int n;
	
	cout<<"Ma tran loai: "<<endl;
	cin>>n;	
	cout<<"Nhap phan tu ma tran"<<endl;
	nhapmatran(a,n);
	
	cout<<"Ket qua"<<endl;
	xuatmatran(a,n);

	cout<<"\nDinh thuc"<<endl;
	cout<<dinhthuc(a,n);
	cout<<endl;

	cout<<"\n Ma tran nghich dao"<<endl;
	nghichdao(a,n);
	cout<<endl;

	
}

[TheIdeasMan]

Hi,

There were some warnings when I compiled with cpp.sh (with all 3 warnings on):

In function 'int nhapmatran(float (*)[100], int)': 
23:1: warning: no return statement in function returning non-void [-Wreturn-type] 
In function 'int xuatmatran(float (*)[100], int)': 
35:1: warning: no return statement in function returning non-void [-Wreturn-type] 
In function 'float nghichdao(float (*)[100], int)': 
83:14: warning: unused variable 't' [-Wunused-variable] 
83:16: warning: variable 'k' set but not used [-Wunused-but-set-variable] 
In function 'int main()': 138:8: warning: unused variable 'b' [-Wunused-variable]

However they don't look as they would cause too many problems. I would fix them though: if there are warnings - one isn't finished :+) always set the warning level as high as you can, warnings are your friend. On g++ or clang use at least -Wall -Wextra -pedantic-errors

I use these ones as well:
http://www.cplusplus.com/forum/general/183731/#msg899203


If it turns out to be a runtime problem, then try to use a debugger, hopefully there is a GUI one in your IDE. This is by far the easiest thing to do, it will save you days of staring at code :+)

Good Luck !!
Lots of good stuff here, written by Bjarne Stroustrup & Herb Sutter:

https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines.html#main