输入一个矩阵(5*5)求矩阵下三角形元素之和，看看这个程序哪里有错？

#include<stdio.h>
#define ROW 5
#define COL 5
int main(){
    int a[ROW][COL],i=0,j=0,sum=0;
    for(i=0;i<ROW;i++){
    for(j=0;j<COL;j++){
    scanf("%d",&a[i][j]);}}
    for(i=0;i<j;i++){
    for(j=0;j<=i;j++){
    sum+=a[i][j];}}
    printf("%d",sum);
    return 0;
    
}

第二个for循环里的i应该小于行数，而不是j

#include<stdio.h>
#define ROW 5
#define COL 5
int main() {
    int a[ROW][COL], i = 0, j = 0, sum = 0;
    for (i = 0; i < ROW; i++) {
        for (j = 0; j < COL; j++) {
            scanf("%d", &a[i][j]);
        }
    }
    //1
    //1 1
    //1 1 1
    //1 1 1 1
    //1 1 1 1 1
    for (i = 0; i < ROW; i++) {
        for (j = 0; j <= i; j++) {
            sum += a[i][j];
        }
    }
    printf("%d", sum);
    return 0;

}

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