//sum is the sum of diagonal elements —————————————————————————————————————————————————————. stdio.h # include & ltstring void main(){ int a[3][3]； int i，j； //i is row j and column intsum = 0; int sum 1 = 0； //Enter for(I = 0；; I < = 2; i++){ for(j = 0； j & lt=2; J++){printf (please enter the number in row %d and column %d:, i+ 1, j+1); scanf (%d，& ampa[I][j])； } printf(\ n)； }//Sum for(I = 0； I < = 2; i++){ for(j = 0； j & lt=2; j++){ if(I = = j)sum = sum+a[I][j]； if(I+j = = 2)sum 1 = sum 1+a[I][j]； }}//Output and print f (sum of diagonal lines from left to right %d\n, sum); Printf (sum of diagonal lines from right to left %d\n, sum1); //diagonal sum; //Output matrix printf (\ n);