best 初始化应赋值1
或者,把if(best<m[i][j])best=m[i][j];放到else外面
> #include"stdio.h"
> #include"stdlib.h"
> int cmp ( const void *a , const void *b ) 
> { 
> return *(int *)a - *(int *)b; 
> } 
> main(){
> 	int a,b,c[100][100],i,j,k[10000],x,m[100][100],n[4],best;
> 	while(scanf("%d %d",&a,&b)==2){
> 		best=0;
> 	for(i=0;i<a;i++)
> 		for(j=0;j<b;j++){
> 			c[i][j]=0;
> 			m[i][j]=0;
> 		}
> 	for(i=0;i<a;i++)
> 		for(j=0;j<b;j++){
> 			scanf("%d",&c[i][j]);
> 			k[b*i+j]=c[i][j];
> 		}
> 	qsort(k,a*b,sizeof(k[0]),cmp); 
> 	for(x=0;x<a*b;x++)
>     	for(i=0;i<a;i++)
> 	    	for(j=0;j<b;j++)
> 				if(c[i][j]==k[x]){
> 					if(c[i][j]==k[0]) m[i][j]=1;
> 					else{
> 						if(j>=1&&c[i][j]>c[i][j-1]) n[0]=m[i][j-1];
> 						else n[0]=0;
> 						if(j+1<b&&c[i][j]>c[i][j+1]) n[1]=m[i][j+1];
> 						else n[1]=0;
> 						if(i>=1&&c[i][j]>c[i-1][j]) n[2]=m[i-1][j];
> 						else n[2]=0;
> 						if(i+1<a&&c[i][j]>c[i+1][j]) n[3]=m[i+1][j];
> 						else n[3]=0;
> 						qsort(n,4,sizeof(n[0]),cmp);
> 						m[i][j]=n[3]+1;
>                         if(best<m[i][j]) best=m[i][j];
> 					}
> 				}
> 	printf("%d\n",best);
> 	}
> }