Daca lucrezi in C, atunci adresarea liniilor si a coloanelor se face de la indexul 0. In cazul in care lucrezi in Pascal atunci o sa inceapa de la 1.
int main()
{
int n, m;
int matrix[n][m];
printf("n=");
scanf("%d",&n);
printf("m=");
scanf("%d",&m);
int i,j;
int suma=0;
for(i=0;i<n;i++){
for(j=0;j<m;j++){
printf("matrix[%d][%d]= ",i,j);
scanf("%d",&matrix[i][j]);
}
}
for(i=0;i<n;i+=2){
for(j=0;j<m;j++){
suma=suma+matrix[i][j];
}
}
printf("Suma= %d",suma);
return 0;
}