#include<stdio.h>
#include<math.h>
#define M 3
#define N 3
/*************** ガウスの消去法プログラム ****************/
int printout(double a[][N], double b[]); 
int printsol(double x[]); 


int main(void){
	int i, j, k; double c,d;
	double a[M][N] = {{1.0,2.0,1.0},{3.0,8.0,7.0},{2.0,7.0,4.0}};
	double b[M] = {3.0,5.0,8.0};
	double x[M] = {0.0,0.0,0.0};

    printout(a,b);
    for(i=0; i<M-1; i++){ c=a[i][i];
        for (k=i+1;k<M;k++) { d=a[k][i]; 
           	for (j=0;j<M; j++){
             a[k][j]=a[k][j]-a[i][j]*d/c;
             } b[k]=b[k]-b[i]*d/c;
		}
     }
	printout(a,b);
    for(i=M-1; i>=0; i--){
          	 for (j=i+1;j<=M-1;j++){
             b[i]=b[i]-a[i][j]*x[j];
             }  x[i]=b[i]/a[i][i]; 
             printf("i=%d, b=%lf a=%lf x=%lf\n",i,a[i][i],b[i],x[i]);
     }
    printsol(x);
	return 0;
}
int printout(double a[M][N], double b[M]) {
	int i,j;
	for (i=0;i<M;i++){
		for (j=0;j<N;j++){ 
        	printf("%7.2lf",a[i][j]);
        	}  printf("%7.2lf\n",b[i]);

    	}   printf("------------------\n");
    return 0;
    }
int printsol(double x[M]) {
	int i;
	for (i=0;i<M;i++){
  	   printf("x[%d]=%7.2lf\n",i+1,x[i]);
    	}   printf("------------------\n");
    return 0;
    }